This directory is intended to hold "experimental" files.

The code in this directory does not necessary work.  It may
or may not be added to future SQLite releases.  We just need
a place to put ideas and works-in-progress and so this 
directory was created.

If you are interested in the production versions of SQLite,
you can safely ignore this directory.

/*
** Copyright (c) 2001 D. Richard Hipp
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the GNU General Public
** License as published by the Free Software Foundation; either
** version 2 of the License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
** General Public License for more details.
** 
** You should have received a copy of the GNU General Public
** License along with this library; if not, write to the
** Free Software Foundation, Inc., 59 Temple Place - Suite 330,
** Boston, MA  02111-1307, USA.
**
** Author contact information:
**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*************************************************************************
** $Id: db.c,v 1.1 2001/02/11 16:56:24 drh Exp $
*/
#include "sqliteInt.h"
#include "pg.h"

/*
** Everything we need to know about an open database
*/
struct Db {
  Pgr *pPgr;            /* The pager for the database */
  DbCursor *pCursor;    /* All open cursors */
  int inTransaction;    /* True if a transaction is in progress */
  u32 freeList;         /* List of free blocks */
  int nTable;           /* Number of slots in aContent[] */
  u32 *aTable;          /* Root page numbers for all tables */
};

/*
** The maximum depth of a cursor
*/
#define MX_LEVEL 10

/*
** Within a cursor, each level off the search tree is an instance of
** this structure.
*/
typedef struct DbIdxpt DbIdxpt;
struct DbIdxpt {
  int pgno;         /* The page number */
  u32 *aPage;       /* The page data */
  int idx;          /* Index into pPage[] */
};

/*
** Everything we need to know about a cursor
*/
struct DbCursor {
  Db *pDb;                      /* The whole database */
  DbCursor *pPrev, *pNext;      /* Linked list of all cursors */
  u32 rootPgno;                 /* Root page of table for this cursor */
  int onEntry;                  /* True if pointing to a table entry */
  int nLevel;                   /* Number of levels of indexing used */
  DbIdxpt aLevel[MX_LEVEL];     /* The index levels */
};

/*
** Data layouts
**
** LEAF:
**    x[0]          Magic number: BLOCK_LEAF
**    x[1]          If root page, total number of entries in this table
**    ...           One or more entries follow the leaf.
**
** Entry:
**    x[N+0]        Number of u32-sized words in this entry
**    x[N+1]        Hash value for this entry
**    x[N+2]        Number of bytes of key in the payload
**    x[N+3]        Number of bytes of data in the payload
**    x{N+4]...     The payload area.
**
** INDEX:
**    x[0]          Magic number: BLOCK_INDEX
**    x[1]          If root page: total number of entries in this table
**    x[2]          Number of slots in this index (Max value of N)
**    x[2*N+3]      Page number containing entries with hash <= x[2*N+4]
**    x[2*N+4]      The maximum hash value for entries on page x[2*N+3].
**
** FREE:
**    x[0]          Magic number: BLOCK_FREE
**    x[1]          Page number of the next free block on the free list
**
** PAGE1:
**    x[0]          Magic number: BLOCK_PAGE1
**    x[1]          First page of the freelist
**    x[2]          Number of tables in this database
**    x[N+3]        Root page for table N

/*
** The first word of every page is some combination of these values
** used to indicate its function.
*/
#define BLOCK_PAGE1            0x24e47191
#define BLOCK_INDEX            0x7ac53b46
#define BLOCK_LEAF             0x60c45eef
#define BLOCK_FREE             0x5b2dda47

/*
** The number of u32-sized objects that will fit on one page.
*/
#define U32_PER_PAGE  (SQLITE_PAGE_SIZE/sizeof(u32))

/*
** Number of direct overflow pages per database entry
*/
#define N_DIRECT  10

/*
** The maximum amount of payload (in bytes) that will fit on on the same
** page as a leaf.  In other words, the maximum amount of payload
** that does not require any overflow pages.
**
** This size is chosen so that a least 3 entry will fit on every 
** leaf.  That guarantees it will always be possible to add a new
** entry after a page split.
*/
#define LOCAL_PAYLOAD (((U32_PER_PAGE-2)/3 - (6+N_DIRECT))*sizeof(u32))

/*
** Allocate a new page.  Return both the page number and a pointer
** to the page data.  The calling function is responsible for unref-ing
** the page when it is no longer needed.
**
** The page is obtained from the freelist if there is anything there.
** If the freelist is empty, the new page comes from the end of the
** database file.
*/
int allocPage(Db *pDb, u32 *pPgno, u32 **ppPage){
  u32 pgno;
  int rc;

  if( pDb->aTable==0 ) return SQLITE_NOMEM;

  /* Try to reuse a page from the freelist
  */
  if( pDb->freeList==0 ){
    u32 *pPage;
    rc = sqlitePgGet(pDb->pPgr, pDb->freeList, &pPage);
    if( rc==SQLITE_OK ){
      if( pPage[0]==BLOCK_FREE ){
        *pPgno = pDb->freeList;
        *ppPage = aPage;
        pDb->freeList = aPage[1];
        memset(*ppPage, 0, SQLITE_PAGE_SIZE);
        return SQLITE_OK;
      }
      /* This only happens if we have database corruption */
      sqlitePgUnref(pPage);
    }
  }

  /* If the freelist is empty, or we cannot access it,
  ** then allocate a new page from the end of the file.
  */
  if( (rc = sqlitePgCount(pDb->pPgr, &pgno))==SQLITE_OK &&
      (rc = sqlitePgGet(pDb->pPgr, pgno, (void**)ppPage))==SQLITE_OK ){
    *pPgno = pgno;
    memset(*ppPage, 0, SQLITE_PAGE_SIZE);
    return SQLITE_OK;
  }
  return rc;
}

/*
** Return a page to the freelist and dereference the page.
*/
static void freePage(DB *pDb, u32 pgno, u32 *aPage){
  if( pgno==0 ) return
  if( aPage==0 ){
    int rc;
    rc = sqlitePgGet(pDb->pPgr, pgno, &aPage);
    if( rc!=SQLITE_OK ) return;
  }
  assert( sqlitePgNum(aPage)==pgno );
  aPage[0] = BLOCK_FREE;
  aPage[1] = pDb->freeList;
  pDb->freeList = pgno;
  memset(&aPage[2], 0, SQLITE_PAGE_SIZE - 2*sizeof(u32));
  sqlitePgTouch(aPage);
  sqlitePgUnref(aPage);
}

/*
** Return the number of bytes of payload storage required on the leaf
** node to hold the amount of payload specified by the argument.
** Overflow pages do not count, only memory on the leaf page.
**
** Return -1 if nTotal is more than sqlite is able to store.
*/
static int payloadLocalSize(int nTotal){
  int nLocal, i;
  if( nTotal<0 ) nTotal = 0;
  if( nTotal <= LOCAL_PAYLOAD ){
    /* All the data fits on the leaf page */
    return (nTotal + 3)/4;
  }
  nLocal = LOCAL_PAYLOAD;
  nTotal -= LOCAL_PAYLOAD;
  if( nTotal < 10*SQLITE_PAGE_SIZE ){
    return nLocal + ((nTotal+SQLITE_PAGE_SIZE-1)/SQLITE_PAGE_SIZE)*sizeof(u32);
  }
  nLocal += N_DIRECT*sizeof(u32);
  nTotal -= N_DIRECT*SQLITE_PAGE_SIZE;
  if( nTotal < U32_PER_PAGE*SQLITE_PAGE_SIZE ){
    return nLocal + sizeof(u32);
  }
  nLocal += sizeof(u32);
  nTotal -= U32_PER_PAGE*SQLITE_PAGE_SIZE;
  if( nTotal < U32_PER_PAGE*U32_PER_PAGE*SQLITE_PAGE_SIZE ){
    return nLocal + sizeof(u32);
  }
  return -1;  /* This payload will not fit. */
}

/*
** Read data from the payload area.
**
** aPage points directly at the beginning of the payload.  No bounds 
** checking is done on offset or amt -- it is assumed that the payload
** area is big enough to accomodate.
*/
static int payloadRead(Db *pDb, u32 *aPage, int offset, int amt, void *pBuf){
  int rc;
  int tomove;
  int i;

  /* First read local data off of the leaf page itself.
  ** This is all that ever happens in 99% of accesses.
  */
  assert( offset>=0 && amt>=0 );
  if( offset < LOCAL_PAYLOAD ){
    /* Data stored directly in the leaf block of the BTree */
    if( amt+offset>LOCAL_PAYLOAD ){
      tomove = LOCAL_PAYLOAD - offset;
    }else{
      tomove = amt;
    }
    memcpy(pBuf, &((char*)aPage)[offset], tomove);
    pBuf = &((char*)pBuf)[tomove];
    offset += tomove;
    amt -= tomove;
    if( amt<=0 ) return SQLITE_OK;
  }
  offset -= LOCAL_PAYLOAD;
  aPage += LOCAL_PAYLOAD/sizeof(aPage[0]);

  /* If not all of the data fits locally, read from the first
  ** ten direct-access overflow pages.
  */
  if( offset < N_DIRECT*SQLITE_PAGE_SIZE ){
    for(i=offset/SQLITE_PAGE_SIZE; i<N_DIRECT && amt>0; i++){
      char *aData;
      base = offset - i*SQLITE_PAGE_SIZE;
      rc = sqlitePgGet(pDb->pPgr, aPage[i], &aData);
      if( rc!=SQLITE_OK ) return rc;
      if( amt+base > SQLITE_PAGE_SIZE ){
        tomove = SQLITE_PAGE_SIZE - base;
      }else{
        tomove = amt;
      }
      memcpy(pBuf, &aData[base], tomove);
      sqlitePgUnref(aData);
      pBuf = &((char*)pBuf)[tomove];
      amt -= tomove;
    }
  }
  offset -= N_DIRECT*SQLITE_PAGE_SIZE;
  aPage += N_DIRECT;

  /* If the first N_DIRECT overflow pages do not contain everything, then
  ** read from an overflow page that is filled with pointer to
  ** U32_PER_PAGE more overflow pages.
  */
  if( offset < U32_PER_PAGE*SQLITE_PAGE_SIZE ){
    u32 *indirPage;
    rc = sqlitePgGet(pDb->pPgr, aPage[0], &indirPage);
    if( rc!=SQLITE_OK ) return rc;
    for(i=offset/SQLITE_PAGE_SIZE; i<U32_PER_PAGE && amt>0; i++){
      int base;
      char *aData;
      base = offset - i*SQLITE_PAGE_SIZE;
      rc = sqlitePgGet(pDb->pPgr, indirPage[idx], &aData);
      if( rc!=SQLITE_OK ) break;
      if( amt+base > SQLITE_PAGE_SIZE ){
        tomove = SQLITE_PAGE_SIZE - base;
      }else{
        tomove = amt;
      }
      memcpy(pBuf, &aData[base], tomove);
      sqlitePgUnref(aData);
      pBuf = &((char*)pBuf)[tomove];
      amt -= tomove;
    }
    sqlitePgUnref(indirPage);
    if( rc!=SQLITE_OK ) return rc;
    if( amt<=0 ) return SQLITE_OK;
  }
  offset -= U32_PER_PAGE*SQLITE_PAGE_SIZE;
  aPage++;

  /* If there is still more data, then read using a double-indirect
  ** overflow.  The overflow page points to U32_PER_PAGE additional
  ** overflow pages, each of which pointer to U32_PER_PAGE more overflow
  ** pages which contain data.
  **
  ** This is hard to test.  To exercise this code, you have to make
  ** a database entry of more than 273336 bytes in side, assuming a
  ** pagesize of 1024 bytes and 10 direct overflow pages.  By the 
  ** time this code runs, you have already used 267 overflow pages.
  */
  if( offset < U32_PER_PAGE*U32_PER_PAGE*SQLITE_PAGE_SIZE ){
    u32 *dblIndirPage;
    rc = sqlitePgGet(pDb->pPgr, aPage[0], &dblIndirPage);
    if( rc!=SQLITE_OK ) return rc;
    i = offset/(U32_PER_PAGE*SQLITE_PAGE_SIZE);
    for(; i<U32_PER_PAGE && amt>0; i++){
      u32 *indirPage;
      int basis;
      int j;
      rc = sqlitePgGet(pDb->pPgr, dblIndirPage[i], &indirPage);
      if( rc!=SQLITE_OK ) break;
      basis = i*U32_PER_PAGE*SQLITE_PAGE_SIZE;
      j = (offset - basis)/SQLITE_PAGE_SIZE;
      for(; j<U32_PER_PAGE && amt>0; j++){
        char *aData;
        base = (offset - basis) - ij*SQLITE_PAGE_SIZE;
        rc = sqlitePgGet(pDb->pPgr, indirPage[j], &aData);
        if( rc!=SQLITE_OK ) break;
        if( amt+base > SQLITE_PAGE_SIZE ){
          tomove = SQLITE_PAGE_SIZE - base;
        }else{
          tomove = amt;
        }
        memcpy(pBuf, &aData[base], tomove);
        sqlitePgUnref(aData);
        pBuf = &((char*)pBuf)[tomove];
        amt -= tomove;
      }
      sqlitePgUnref(indirPage);
      if( rc!=SQLITE_OK ) break;
    }
    sqlitePgUnref(dblIndirPage);
  }

  /* Anything beyond the double-indirect pages, just fill in with
  ** zeros.  You have to write 67382200 bytes to go past the
  ** double-indirect pages, assuming a 1024 byte page size.
  */
  if( amt>0 ) memset(pBuf, 0, amt);
  return SQLITE_OK;
}

/*
** Write data into the payload area.
**
** If pages have already been allocated for the payload, they are
** simply overwritten.  New pages are allocated as necessary to
** fill in gaps.  sqlitePgTouch() is called on all overflow pages,
** but the calling function must invoke sqlitePgTouch() for aPage
** itself.
*/
static int payloadWrite(Db *pDb, u32 *aPage, int offset, int amt, void *pBuf){
  assert( offset>=0 && amt>=0 );

  /* Local data
  */
  if( offset < LOCAL_PAYLOAD ){
    if( amt+offset>LOCAL_PAYLOAD ){
      tomove = LOCAL_PAYLOAD - offset;
    }else{
      tomove = amt;
    }
    memcpy(&((char*)aPage)[offset], pBuf, tomove);
    pBuf = &((char*)pBuf)[tomove];
    offset += tomove;
    amt -= tomove;
    if( amt<=0 ) return SQLITE_OK;
  }
  offset -= LOCAL_PAYLOAD;
  aPage += LOCAL_PAYLOAD/sizeof(aPage[0]);

  /* Direct overflow pages
  */
  if( offset < N_DIRECT*SQLITE_PAGE_SIZE ){
    for(i=offset/SQLITE_PAGE_SIZE; i<N_DIRECT && amt>0; i++){
      base = offset - i*SQLITE_PAGE_SIZE;
      if( aPage[i] ){
        rc = sqlitePgGet(pDb->pPgr, aPage[i], &aData);
      }else{
        rc = allocPage(pDb, &aPage[i], &aData);
      }
      if( rc!=SQLITE_OK ) return rc;
      if( amt+base > SQLITE_PAGE_SIZE ){
        tomove = SQLITE_PAGE_SIZE - base;
      }else{
        tomove = amt;
      }
      memcpy(&aData[base], pBuf, tomove);
      sqlitePgTouch(aData);
      sqlitePgUnref(aData);
      pBuf = &((char*)pBuf)[tomove];
      amt -= tomove;
    }
    if( amt<=0 ) return SQLITE_OK;
  }
  offset -= N_DIRECT*SQLITE_PAGE_SIZE;
  aPage += N_DIRECT;

  /* Indirect overflow pages
  */
  if( offset < U32_PER_PAGE*SQLITE_PAGE_SIZE ){
    u32 *indirPage;
    if( aPage[0] ){
      rc = sqlitePgGet(pDb->pPgr, aPage[0], &indirPage);
    }else{
      rc = allocPage(pDb, &aPage[0], &indirPage);
    }
    if( rc!=SQLITE_OK ) return rc;
    for(i=offset/SQLITE_PAGE_SIZE; i<U32_PER_PAGE && amt>0; i++){
      int base;
      char *aData;
      base = offset - i*SQLITE_PAGE_SIZE;
      if( indirPage[i] ){
        rc = sqlitePgGet(pDb->pPgr, indirPage[i], &aData);
      }else{
        rc = allocPage(pDb, &indirPage[i], &aData);
        sqlitePgTouch(indirPage);
      }
      if( rc!=SQLITE_OK ) break;
      if( amt+base > SQLITE_PAGE_SIZE ){
        tomove = SQLITE_PAGE_SIZE - base;
      }else{
        tomove = amt;
      }
      memcpy(&aData[base], pBuf, tomove);
      sqlitePgUnref(aData);
      pBuf = &((char*)pBuf)[tomove];
      amt -= tomove;
    }
    sqlitePgUnref(indirPage);
    if( rc!=SQLITE_OK ) return rc;
    if( amt<=0 ) return SQLITE_OK;
  }
  offset -= U32_PER_PAGE*SQLITE_PAGE_SIZE;
  aPage++;

  /* Double-indirect overflow pages
  */
  if( offset < U32_PER_PAGE*U32_PER_PAGE*SQLITE_PAGE_SIZE ){
    u32 *dblIndirPage;
    if( aPage[0] ){
      rc = sqlitePgGet(pDb->pPgr, aPage[0], &dblIndirPage);
    }else{
      rc = allocPage(pDb, &aPage[0], &dblIndirPage);
    }
    if( rc!=SQLITE_OK ) return rc;
    i = offset/(U32_PER_PAGE*SQLITE_PAGE_SIZE);
    for(; i<U32_PER_PAGE && amt>0; i++){
      u32 *indirPage;
      int basis;
      int j;
      if( aPage[0] ){
        rc = sqlitePgGet(pDb->pPgr, aPage[0], &dblIndirPage);
      }else{
        rc = allocPage(pDb, &aPage[0], &dblIndirPage);
        sqlitePgTouch(dblIndirPage);
      }
      rc = sqlitePgGet(pDb->pPgr, dblIndirPage[i], &indirPage);
      if( rc!=SQLITE_OK ) break;
      basis = i*U32_PER_PAGE*SQLITE_PAGE_SIZE;
      j = (offset - basis)/SQLITE_PAGE_SIZE;
      for(; j<U32_PER_PAGE && amt>0; j++){
        char *aData;
        base = (offset - basis) - ij*SQLITE_PAGE_SIZE;
        if( indirPage[j] ){
          rc = sqlitePgGet(pDb->pPgr, indirPage[j], &aData);
        }else{
          rc = allocPage(pDb, &indirPage[j], &aData);
          sqlitePgTouch(indirPage);
        }
        if( rc!=SQLITE_OK ) break;
        if( amt+base > SQLITE_PAGE_SIZE ){
          tomove = SQLITE_PAGE_SIZE - base;
        }else{
          tomove = amt;
        }
        memcpy(&aData[base], pBuf, tomove);
        sqlitePgTouch(aData);
        sqlitePgUnref(aData);
        pBuf = &((char*)pBuf)[tomove];
        amt -= tomove;
      }
      sqlitePgUnref(indirPage);
      if( rc!=SQLITE_OK ) break;
    }
    sqlitePgUnref(dblIndirPage);
  }

  return SQLITE_OK;
}

/*
** Resize the payload area.  If the payload area descreases in size,
** this routine deallocates unused overflow pages.  If the payload
** area increases in size, this routine is a no-op.
*/
static int payloadResize(Db *pDb, u32 *aPage, int oldSize, int newSize){
  int i, j;          /* Loop counters */
  int first, last;   /* Indices of first and last pages to be freed */
  int rc;            /* Return code from sqlitePgGet() */

  /* Skip over the local data.  We do not need to free it.
  */
  if( newSize>=oldSize ) return SQLITE_OK;
  oldSize -= LOCAL_PAYLOAD;
  if( oldSize<=0 ) return SQLITE_OK;
  newSize -= LOCAL_PAYLOAD;
  aPage += LOCAL_PAYLOAD/sizeof(u32);

  /* Compute the indices of the first and last overflow pages to
  ** be freed.
  */
  first = (newSize - 1)/SQLITE_PAGE_SIZE + 1;
  last = (oldSize - 1)/SQLITE_PAGE_SIZE;

  /* Free the direct overflow pages
  */
  if( first < N_DIRECT ){
    for(i=first; i<N_DIRECT && i<=last; i++){
      freePage(pDb, aPage[i], 0);
      aPage[i] = 0;
    }
  }
  aPage += N_DIRECT;
  first -= N_DIRECT;
  last -= N_DIRECT;
  if( last<0 ) return SQLITE_OK;
  if( first<0 ) first = 0;
  
  /* Free indirect overflow pages
  */
  if( first < U32_PER_PAGE ){
    u32 *indirPage;
    rc = sqlitePgGet(pDb->pPgr, aPage[0], &indirPage);
    if( rc!=SQLITE_OK ) return rc;
    for(i=first; i<U32_PER_PAGE && i<=last; i++){
      freePage(pDb, indirPage[i], 0);
      indirPage[i] = 0;
      touch = 1;
    }
    if( first<=0 ){
      freepage(pDb, aPage[0], indirPage);
      aPage[0] = 0;
    }else{
      sqlitePgTouch(indirPage);
      sqlitePgUnref(indirPage);
    }
  }
  aPage++;
  first -= U32_PER_PAGE;
  last -= U32_PER_PAGE;
  if( last<0 ) return SQLITE_OK;
  if( first<0 ) first = 0;

  /* Free double-indirect overflow pages
  */
  if( first < U32_PER_PAGE*U32_PER_PAGE ){
    u32 *dblIndirPage;
    rc = sqlitePgGet(pDb->pPgr, aPage[0], &dblIndirPage);
    if( rc!=SQLITE_OK ) return rc;
    for(i=first/U32_PER_PAGE; i<U32_PER_PAGE; i++){
      u32 *indirPage;
      basis = i*U32_PER_PAGE;
      if( last < basis ) break;
      rc = sqlitePgGet(pDb->pPgr, dblIndirPage[i], &indirPage);
      if( rc!=SQLITE_OK ) return rc;
      for(j=first>basis?first-basis:0 ; j<U32_PER_PAGE; j++){
        if( j + basis > last ) break;
        freePage(pDb, indirPage[j], 0);
        indirPage[j] = 0;
      }
      if( first<=basis ){
        freepage(pDb, dblIndirPage[i], 0);
        dblIndirPage[i] = 0;
      }else{
        sqlitePgTouch(indirPage);
        sqlitePgUnref(indirPage);
      }
    }
    if( first<=0 ){
      freepage(pDb, aPage[0], dblIndirPage);
      aPage[0] = 0;
    }else{
      sqlitePgTouch(dblIndirPage);
      sqlitePgUnref(dblIndirPage);
    }
  }

  return SQLITE_OK;    
}

/*
** Allocate space for the content table in the given Db structure.
** return SQLITE_OK on success and SQLITE_NOMEM if it fails.
*/
static int sqliteDbExpandTableArray(Db *pDb){
  pDb->aTable = sqliteRealloc( pDb->aTable, pDb->nTable*sizeof(u32));
  if( pDb->aTable==0 ){
    pDb->inTranaction = 0;
    return SQLITE_NOMEM;
  }
  return SQLITE_OK;
}

/*
** Open a database.
*/
int sqliteDbOpen(const char *filename, Db **ppDb){
  Db *pDb = 0;
  Pgr *pPgr = 0;
  u32 *aPage1;
  int rc;
  u32 nPage;

  rc = sqlitePgOpen(filename, &pPgr);
  if( rc!=SQLITE_OK ) goto open_err;
  pDb = sqliteMalloc( sizeof(*pDb) );
  if( pDb==0 ){
    rc = SQLITE_NOMEM;
    goto open_err;
  }
  pDb->pPgr = pPgr;
  pDb->pCursor = 0;
  pDb->inTransaction = 0;
  sqlitePgCount(pDb->pPgr, &nPage);
  rc = sqlitePgGet(pDb->pPgr, 1, &aPage1);
  if( rc!=0 ) goto open_err;
  if( nPage==0 ){
    sqlitePgBeginTransaction(pDb->pPgr);
    aPage1[0] = BLOCK_PAGE1;
    sqlitePgTouch(aPage1);
    sqlitePgCommit(pDb->pPgr);
  }
  pDb->freeList = aPage[1];
  pDb->nTable = aPage[2];
  rc = sqliteDbExpandTableArray(pDb);
  if( rc!=SQLITE_OK ) goto open_err;
  rc = payloadRead(pDb, &aPage1[3], 0, pDb->nTable*sizeof(u32), pDb->aTable);
  sqlitePgUnref(aPage1);
  if( rc!=SQLITE_OK ) goto open_err;
  *ppDb = pDb;
  return SQLITE_OK;

open_err:
  *ppDb = 0;
  if( pPgr ) sqlitePgClose(pPgr);
  if( pDb ){
    sqliteFree(pDb->aContent);
    sqliteFree(pDb);
  }
  return rc;
}

/*
** Close a database
*/
int sqliteDbClose(Db *pDb){
  while( pDb->pCursor ){
    sqliteDbCursorClose(pDb->pCursor);
  }
  sqlitePgClose(pDb->pPgr);
  sqliteFree(pDb->aContent);
  sqliteFree(pDb);
  return SQLITE_OK;
}

/*
** Begin a transaction
*/
int sqliteDbBeginTransaction(Db *pDb){
  int rc;
  if( pDb->aContent==0 ){
    return SQLITE_NOMEM;
  }
  if( pDb->inTransaction ){
    return SQLITE_INTERNAL;
  }
  rc = sqlitePgBeginTransaction(pDb->pPgr);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  pDb->inTransaction = 1;
  return SQLITE_OK;
}

/*
** Commit changes to the database
*/ 
int sqliteDbCommit(Db *pDb){
  u32 *aPage1;
  int rc;
  if( !pDb->inTransaction ){
    return SQLITE_OK;
  }
  rc = sqlitePgGet(pDb->pPgr, 1, &aPage1);
  if( rc!=SQLITE_OK ) return rc;
  aPage1[1] = pDb->freeList;
  aPage1[2] = pDb->nTable;
  payloadWrite(pDb, &aPage1[3], 0, pDb->nTable*sizeof(u32), pDb->aTable);
  sqlitePgUnref(aPage1);
  rc = sqlitePgCommit(pDb->pPgr);
  if( rc!=SQLITE_OK ) return rc;
  pDb->inTransaction = 0;
  return SQLITE_OK;
}

/*
** Rollback the database to its state prior to the beginning of
** the transaction
*/
int sqliteDbRollback(Db *pDb){
  u32 *aPage1;
  if( !pDb->inTransaction ) return SQLITE_OK;
  rc = sqlitePgRollback(pDb->pPgr);
  if( rc!=SQLITE_OK ) return rc;
  rc = sqlitePgGet(pDb->pPgr, 1, &aPage1);
  if( rc!=SQLITE_OK ) return rc;
  pDb->freeList = aPage1[1];
  pDb->nTable = aPage1[2];
  if( sqliteDbExpandTableArray(pDb)!=SQLITE_OK ){
    return SQLITE_NOMEM;
  }
  payloadRead(pDb, &aPage1[3], 0, pDb->nTable*sizeof(u32), pDb->aTable);
  sqlitePgUnref(aPage1);
  pDb->inTransaction = 0;
  return SQLITE_OK;
}

/*
** Create a new table in the database.  Write the table number
** that is used to open a cursor into that table into *pTblno.
*/
int sqliteDbCreateTable(Db *pDb, int *pTblno){
  u32 *aPage;
  u32 pgno;
  int rc;
  int swTblno;
  int i;

  rc = allocPage(pDb, &pgno, &aPage);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  tblno = -1;
  for(i=0; i<pDb->nTable; i++){
    if( pDb->aTable[i]==0 ){
      tblno = i;
      break;
    }
  }
  if( tblno<0 ){
    pDb->nTable++;
    rc = sqliteExpandTableArray(pDb);
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }
  pDb->aTable[tblno] = pgno;
  aPage[0] = BLOCK_LEAF;
  memset(&aPage[1], 0, SQLITE_PAGE_SIZE - sizeof(u32));
  sqlitePgTouch(aPage);
  sqlitePgUnref(aPage);
  return rc;
}

/*
** Recursively add a page to the free list
*/
static int sqliteDbDropPage(Db *pDb, u32 pgno){
  u32 *aPage;
  int rc;

  rc = sqlitePgGet(pDb->pPgr, pgno, (void**)&aPage);
  if( rc!=SQLITE_OK ) return rc;
  switch(  aPage[0] ){
    case BLOCK_INDEX: {
      int n, i;
      n = aPage[2];
      for(i=0; i<n; i++){
        u32 subpgno = aPage[3 + i*2];
        if( subpgno>0 ) sqliteDbDropPage(pDb, subpgno);
      }
      freePage(pDb, pgno, aPage);
      break;
    }
    case BLOCK_LEAF: {
      int i = 2;
      while( i<U32_PER_PAGE ){
        int entrySize = aPage[i];
        if( entrySize==0 ) break;
        payloadResize(pDb, &aPage[i+4], aPage[i+2]+aPage[i+3], 0);
        i += entrySize;
      }
      freePage(pDb, pgno, aPage);
      break;
    }
    default: {
      /* Do nothing */
      break;
    }
  }
}

/*
** Delete the current associate of a cursor and release all the
** pages it holds.  Except, do not release pages at levels less
** than N.
*/
static void sqliteDbResetCursor(DbCursor *pCur, int N){
  int i;
  for(i=pCur->nLevel-1; i>=N; i--){
    sqlitePgUnref(pCur->aLevel[i].aPage);
  }
  pCur->nLevel = N;
  pCur->onEntry = 0;
}

/*
** Delete an entire table.
*/
static int sqliteDbDropTable(Db *pDb, int tblno){
  DbCursor *pCur;
  u32 pgno;

  /* Find the root page for the table to be dropped.
  */
  if( pDb->aTable==0 ){
    return SQLITE_NOMEM;
  }
  if( tblno<0 || tblno>=pDb->nTable || pDb->aTable[tblno]==0 ){
    return SQLITE_NOTFOUND;
  }
  pgno = pDb->aTable[tblno];
  pDb->aTable[tblno] = 0;
  if( tblno==pDb->nTable-1 ){
    pDb->nTable--;
  }

  /* Reset any cursors pointing to the table that is about to
  ** be dropped */
  for(pCur=pDb->pCursor; pCur; pCur=pCur->pNext){
    if( pCur->rootPgno==pgno ){
      sqliteDbResetCursor(pCur, 0);
    }
  }

  /* Move all pages associated with this table to the freelist
  */
  sqliteDbDropPage(pDb, pgno);
  return SQLITE_OK;
}

/*
** Create a new cursor
*/
int sqliteDbCursorOpen(Db *pDb, int tblno, DbCursor **ppCur){
  u32 pgno;
  DbCursor *pCur;

  /* Translate the table number into a page number
  */
  if( pDb->aTable==0 ){
    *ppCur = 0;
    return SQLITE_NOMEM;
  }
  if( tblno<0 || tblno>=pDb->nContent || pDb->aTable[tblno]==0 ){
    *ppCur = 0;
    return SQLITE_NOTFOUND;
  }
  pgno = pDb->aTable[tblno];
  
  /* Allocate the cursor
  */
  pCur = sqliteMalloc( sizeof(*pCur) );
  pCur->pgno = pgno;
  pCur->pDb = pDb;
  pCur->pNext = pDb->pCursor;
  pCur->pPrev = 0;
  if( pDb->pCursor ){
     pDb->pCursor->pPrev = pCur;
  }
  pDb->pCursor = pCur;
  *ppCur = pCur;
  return SQLITE_OK;
}

/*
** Delete a cursor
*/
int sqliteDbCursorClose(DbCursor *pCur){
  int i;
  if( pCur->pPrev ){
    pCur->pPrev->pNext = pCur->pNext;
  }else if( pCur->pDb->pCursor==pCur ){
    pCur->pDb->pCursor = pCur->pNext;
  }
  if( pCur->pNext ){
    pCur->pNext->pPrev = pCur->pPrev;
  }
  sqliteDbResetCursor(pCur, 0);
  sqliteFree(pCur);
  return SQLITE_OK; 
}

/*
** Beginning at index level "i" (the outer most index is 0), move down 
** to the first entry of the table.  Levels above i (less than i) are 
** unchanged.
*/
static int sqliteDbGotoFirst(DbCursor *pCur, int i){
  int rc = -1;

  assert( i>=0 && i<MAX_LEVEL );
  if( pCur->nLevel > i+1 ){
    sqliteDbResetCursor(pCur, i+1);
  }
  assert( pCur->nLevel==i+1 );
  while( rc < 0 ){
    u32 *aPage = pCur->aLevel[i].aPage;
    assert( aPage!=0 );
    switch( aPage[0] ){
      case BLOCK_LEAF: {
        if( aPage[2]!=0 ){
          pCur->aLevel[i].idx = 2;
          pCur->onEntry = 1;
        }else{
          sqliteDbResetCursor(pCur, 1);
        }
        rc = SQLITE_OK;
        break;
      }
      case BLOCK_INDEX: {
        int n = aPage[2];
        if( n<2 || n>=((U32_PER_PAGE - 3)/2) ){
          sqliteDbResetCur(pCur, 1);
          rc = SQLITE_CORRUPT;
          break;
        }
        pCur->nLevel++;
        i++;
        pCur->aLevel[i].pgno = aPage[3];
        rc = sqlitePgGet(pCur->pDb->pPgr, pCur->aLevel[i].pgno,
                    &pCur->aLevel[i].aPage);
        if( rc != SQLITE_OK ){
          sqliteDbResetCursor(pCur, 1);
        }else{
          rc = -1;
        }
        break;
      }
      default: {
        sqliteDbResetCursor(pCur, 1);
        rc = SQLITE_CORRUPT;
      }
    }
  }
  return rc;
}

################

/*
** Move the cursor to the first entry in the table.
*/
int sqliteDbCursorFirst(DbCursor *pCur){
  if( pCur->nLevel==0 ){
    int rc;
    pCur->aLevel[0].pgno = pCur->rootPgno;
    rc = sqlitePgGet(pCur->pDb->pPgr, pCur->rootPgno, pCur->aLevel[0].aPage);
    if( rc!=SQLITE_OK ){
      sqliteDbResetCursor(pCur, 0);
      return rc;
    }
    pCur->nLevel = 1;
  }
  return sqliteDbGotoFirst(pCur, 0);
}

/*
** Advance the cursor to the next entry in the table.
*/
int sqliteDbCursorNext(DbCursor *pCur){
  int i, idx, n, rc;
  u32 pgno, *aPage;
  if( !pCur->onEntry ){
     return sqliteDbCursorFirst(pCur);
  }
  i = pCur->nLevel-1;
  aPage = pCur->aLevel[i].aPage;
  idx = pCur->aLevel[i].idx;
  idx += SWB(aPage[idx]);
  if( idx >= SQLITE_PAGE_SIZE/sizeof(u32) ){
    sqliteDbResetCursor(pCur, 1);
    return SQLITE_CORRUPT;
  }
  if( aPage[idx]!=0 ){
    pCur->aLabel[i].idx = idx;
    return SQLITE_OK;
  }
  rc = SQLITE_OK;
  while( pCur->nLevel>1 ){
    pCur->nLevel--;
    i = pCur->nLevel-1;
    sqlitePgUnref(pCur->aLevel[pCur->nLevel].aPage);
    aPage = pCur->aLevel[i].aPage;
    idx = pCur->aLevel[i].idx;
    assert( SWB(aPage[0])==BLOCK_MAGIC|BLOCK_INDEX );
    n = SWB(aPage[2]);
    idx += 2;
    if( (idx-3)/2 < n ){
      pCur->aLevel[i].idx = idx;
      pCur->nLevel++;
      i++;
      pgno = pCur->aLevel[i].pgno = SWB(aPage[idx+1]);
      rc = sqlitePgGet(pDb->pPgr, pgno, &pCur->aLevel[i].aPage);
      if( rc!=SQLITE_OK ) break;
      rc = sqliteDbGotoFirst(pCur, i);
      break;
    }
  }
  sqliteDbResetCursor(pCur, 0);
  return SQLITE_OK;
}

/*
** Return the amount of data on the entry that the cursor points
** to.
*/
int sqliteDbCursorDatasize(DbCursor *pCur){
  u32 *aPage;
  int idx, i;
  if( !pCur->onEntry ) return 0;
  i = pCur->nLevel-1;
  idx = pCur->aLevel[i].idx;
  aPage = pCur->aLevel[i].aPage;
  assert( aPage );
  assert( idx>=2 && idx+4<U32_PER_PAGE );
  return aPage[idx+3];
}

/*
** Return the number of bytes of key on the entry that the cursor points
** to.
*/
int sqliteDbCursorKeysize(DbCursor *pCur){
  u32 *aPage;
  int idx, i;
  if( !pCur->onEntry ) return 0;
  i = pCur->nLevel-1;
  idx = pCur->aLevel[i].idx;
  aPage = pCur->aLevel[i].aPage;
  assert( aPage );
  assert( idx>=2 && idx+4<U32_PER_PAGE );
  return aPage[idx+2];
}

/*
** Read data from the cursor.
*/
int sqliteDbCursorRead(DbCursor *pCur, int amt, int offset, void *buf){
  u32 *aPage;
  int idx, i;
  int nData;
  int nKey;
  if( !pCur->onEntry ){
    memset(cbuf, 0, amt);
    return SQLITE_OK;
  }
  if( amt<=0 || offset<0 ){
    return SQLITE_ERR;
  }
  i = pCur->nLevel-1;
  idx = pCur->aLevel[i].idx;
  aPage = pCur->aLevel[i].aPage;
  assert( aPage );
  assert( idx>=2 && idx+4<U32_PER_PAGE );
  nData = aPage[idx+3];
  if( offset>=nData ){
    memset(buf, 0, amt);
    return SQLITE_OK;
  }
  nKey = aPage[idx+2];
  if( nData<offset+amt ){
    memset(&((char*)buf)[nData-offset], 0, amt+offset-nData);
    amt = nData - offset;
  }
  payloadRead(pCur->pDb, &aPage[idx+4], amt, offset + nKey, buf);
  return SQLITE_OK;
}

/*
** Read the current key from the cursor.
*/
int sqliteDbCursorReadKey(DbCursor *pCur, int amt, int offset, void *buf){
  u32 *aPage;
  int idx, i;
  int nData;
  int nKey;
  if( !pCur->onEntry ){
    memset(cbuf, 0, amt);
    return SQLITE_OK;
  }
  if( amt<=0 || offset<0 ){
    return SQLITE_ERR;
  }
  i = pCur->nLevel-1;
  idx = pCur->aLevel[i].idx;
  aPage = pCur->aLevel[i].aPage;
  assert( aPage );
  assert( idx>=2 && idx+4<(SQLITE_PAGE_SIZE/sizeof(u32))
  nKey = aPage[idx+2];
  if( offset>=nKey ){
    memset(buf, 0, amt);
    return SQLITE_OK;
  }
  if( nKey<offset+amt ){
    memset(&((char*)buf)[nKey-offset], 0, amt+offset-nKey);
    amt = nKey - offset;
  }
  payloadRead(pCur->pDb, &aPage[idx+4], amt, offset, buf);
  return SQLITE_OK;
}

/*
** Generate a 32-bit hash from the given key.
*/
static u32 sqliteDbHash(int nKey, void *pKey){
  u32 h;
  unsigned char *key;
  if( nKey==4 ){
    return *(u32*)pKey;
  }
  key = pKey;
  h = 0;
  while( 0 < nKey-- ){
    h = (h<<13) ^ (h<<3) ^ h ^ *(key++)
  }
  return h;
}

/*
** Move the cursor so that the lowest level is the leaf page that
** contains (or might contain) the given key.
*/
static int sqliteDbFindLeaf(DbCursor *pCur, int nKey, void *pKey, u32 h;){
  int i, j, rc;
  u32 h;

  h = sqliteDbHash(nKey, pKey);
  sqliteDbResetCursor(pCur, 1);
  i = 0;
  for(;;){
    u32 nxPgno;
    u32 *aPage = pCur->aLevel[i].aPage;
    if( SWB(aPage[0])==BLOCK_MAGIC|BLOCK_LEAF ) break;
    if( SWB(aPage[0])!=BLOCK_MAGIC|BLOCK_INDEX ){
      return SQLITE_CORRUPT;
    }
    if( i==MAX_LEVEL-1 ){
      return SQLITE_FULL;
    }
    n = SWB(aPage[2]);
    if( n<2 || n>=(SQLITE_PAGE_SIZE/2*sizeof(u32))-2 ){
      return SQLITE_CORRUPT;
    }
    for(j=0; j<n-1; j++){
      if( h < SWB(aPage[j*2+3]) ) break;
    }
    nxPgno = SWB(aPage[j*2+4]);
    pCur->aLevel[i].idx = j;
    pCur->aLevel[i].pgno = nxPgno;
    rc = sqlitePgGet(pCur->pDb->pPgr, nxPgno, &pCur->aLevel[i].aPage);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    pCur->nLevel++;
    i++;
  }
  return SQLITE_OK;
}

/*
** Position the cursor on the entry that matches the given key.
*/
int sqliteDbCursorMoveTo(DbCursor *pCur, int nKey, void *pKey){
  int rc, i;
  u32 *aPage;
  int idx;
  u32 h;

  h = sqliteDbHash(nKey, pKey);
  rc = sqliteDbFindLeaf(pCur, nKey, pKey, h);
  if( rc!=SQLITE_OK ) return rc;
  i = pCur->nLevel-1;
  aPage = pCur->aLevel[i].aPage;
  idx = 2;
  rc = SQLITE_NOTFOUND;
  while( idx>=2 && idx<(SQLITE_PAGE_SIZE/sizeof(u32))-3 && aPage[idx]!=0 ){
    if( sqliteDbKeyMatch(&aPage[idx], nKey, pKey, h) ){
      pCur->aLevel[i].idx = idx;
      pCur->onEntry = 1;
      rc = SQLITE_OK;
      break;
    }
    idx += SWB(aPage[idx]);
  }
  return rc;
}

/*
** Insert a new entry into the table.  The cursor is left pointing at
** the new entry.
*/
int sqliteDbCursorInsert(   
   DbCursor *pCur,          /* A cursor on the table in which to insert */
   int nKey, void *pKey,    /* The insertion key */
   int nData, void *pData   /* The data to be inserted */
){
  int minNeeded, maxNeeded;    /* In u32-sized objects */
  int rc;
  u32 h;
  int available;
  int i, j, k;
  int nKeyU, nDataU;
  u32 *aPage;
  int incr = 1;

  /* Null data is the same as a delete.
  */
  if( nData<=0 || pData==0 ){
    if( sqliteDbCursorMoveTo(pCur, nKey, pKey);
      return sqliteDbCursorDelete(pCur);
    }else{
      return SQLITE_OK;
    }
  }

  /* Figure out how much free space is needed on a leaf block in order
  ** to hold the new record.
  */
  minNeeded = maxNeeded = 6;
  nKeyU = (nKey+3)/4;
  nDataU = (nData+3)/4;
  if( nKeyU + maxNeeded + 2 <= SQLITE_PAGE_SIZE/sizeof(u32) ){
    maxNeeded += nKeyU;
  }
  if( nKeyU < SQLITE_PAGE_SIZE/(3*sizeof(u32)) ){
    minNeeded += nKeyU;
  }
  if( nDataU + maxNeeded + 2 <= SQLITE_PAGE_SIZE/sizeof(u32) ){
    maxNeeded += nDataU
  }
  if( nDataU < SQLITE_PAGE_SIZE/(3*sizeof(u32)) ){
    minNeeded += nDataU;
  }

  /* Move the cursor to the leaf block where the new record will be
  ** inserted.
  */
  h = sqliteDbHash(nKey, pKey);
  rc = sqliteDbFindLeaf(pCur, nKey, pKey, h);
  if( rc!=SQLITE_OK ) return rc;

  /* Walk thru the leaf once and do two things:
  **   1.  Remove any prior entry with the same key.
  **   2.  Figure out how much space is available on this leaf.
  */
  i = j = 2;
  aPage = pCur->aLevel[pCur->nLevel-1].aPage;
  for(;;){
    int entrySize = SWB(aPage[i]);
    if( entrySize<=0 || entrySize + i >= SQLITE_PAGE_SIZE/sizeof(u32) ) break;
    if( !sqliteDbKeyMatch(&aPage[i], nKey, pKey, h) ){
      if( j<i ){
        for(k=0; k<entrySize; k++){
           aPage[j+k] = aPage[i+k];
        }
      }
      j += entrySize;
    }else{
      sqliteDbClearEntry(pCur->pDb, &aPage[i]);
      incr--;
    }
    i += entrySize;
  }
  available = SQLITE_PAGE_SIZE/sizeof(u32) - j;

  /* If the new entry will not fit, try to move some of the entries
  ** from this leaf onto sibling leaves.
  */
  if( available<minNeeded ){
    int newSpace;
    newSpace = sqliteDbSpreadLoad(pCur, maxNeeded); ############
    available += newSpace;
  }

  /* If the new entry still will not fit, try to split this leaf into
  ** two adjacent leaves.
  */
  if( available<minNeeded && pCur->nLevel>1 ){
    int newAvail;
    newAvail = sqliteDbSplit(pCur, maxNeeded); ##############
    if( newAvail>0 ){
      available += newAvail;
    }
  }

  /* If the new entry does not fit after splitting, turn this leaf into
  ** and index node with one leaf, go down into the new leaf and try 
  ** to split again.
  */
  if( available<minNeeded && pCur->nLevel<MAX_LEVEL-1 ){
    int newAvail;
    sqliteDbNewIndexLevel(pCur);  ###############
    newAvail = sqliteDbSplit(pCur, maxNeeded);
    if( newAvail>0 ){
      available = newAvail;
    }
  }

  /* If the entry still will not fit, it means the database is full.
  */
  if( available<minNeeded ){
    return SQLITE_FULL;
  }

  /* Add the new entry to the leaf block.
  */
  aPage = pCur->aLevel[pCur->nLevel-1].aPage;
  i = 2;
  for(;;){
    int entrySize = SWB(aPage[i]);
    if( entrySize<=0 || entrySize + i >= SQLITE_PAGE_SIZE/sizeof(u32) ) break;
    i += entrySize;
  }
  assert( available==SQLITE_PAGE_SIZE/sizeof(u32) - i );
  aPage[i+1] = SWB(h);
  available -= 5;
  if( nKeyU <= available ){
    aPage[i+2] = SWB(nKey);
    memcpy(&aPage[i+4], pKey, nKey);
    j = i + 4 + nKeyU;
    available -= nKeyU;
  }else{
    u32 newPgno, *newPage;
    aPage[i+2] = SWB(nKey | 0x80000000);
    rc = allocPage(pCur->pDb, &newPgno, &newPage);
    if( rc!=SQLITE_OK ) goto write_err;
    aPage[i+4] = SWB(newPgno);
    newPage[0] = SWB(BLOCK_MAGIC | BLOCK_OVERFLOW);
    rc = sqliteDbWriteOvfl(pCur->pDb, newPage, nKey, pKey);
    if( rc!=SQLITE_OK ) goto write_err;
    j = i + 5;
    available -= 1;
  }
  if( nDataU <= available ){
    aPage[i+3] = SWB(nData);
    memcpy(&aPage[j], pData, nData);
    available -= nDataU;
    j += nDataU;
  }else{
    u32 newPgno, *newPage;
    aPage[i+3] = SWB(nData | 0x80000000);
    rc = allocPage(pCur->pDb, &newPgno, &newPage);
    if( rc!=SQLITE_OK ) goto write_err;
    aPage[j] = SWB(newPgno);
    newPage[0] = SWB(BLOCK_MAGIC | BLOCK_OVERFLOW);
    rc = sqliteDbWriteOvfl(pCur->pDb, newPage, nData, pData);
    if( rc!=SQLITE_OK ) goto write_err;
    available -= 1;
    j++;
  }    
  if( j<SQLITE_PAGE_SIZE/sizeof(u32) ){
    aPage[j] = 0;
  }
  sqlitePgTouch(aPage);
  pCur->aLevel[pCur->nLevel-1].idx = i;
  pCur->onEntry = 1;

  /*  Increment the entry count for this table.
  */
  if( incr!=0 ){
    pCur->aLevel[0].aPage[1] = SWB(SWB(pCur->aLevel[0].aPage[1])+incr);
    sqlitePgTouch(pCur->aLevel[0].aPage);
  }
  return SQLITE_OK;

write_err:
  aPage[i] = 0;
  pCur->onEntry = 0;
  return rc;
}

/*
** Delete the entry that the cursor points to.
*/
int sqliteDbCursorDelete(DbCursor *pCur){
  int i, idx;
  int from, to, limit, n;
  int entrySize;
  u32 *aPage;
  if( !pCur->onEntry ) return SQLITE_NOTFOUND;

  /* Delete the entry that the cursor is pointing to.
  */
  i = pCur->nLevel - 1;
  aPage = pCur->aLevel[i].aPage;
  idx = pCur->aLevel[i].idx;
  assert( SWB(aPage[0])==BLOCK_MAGIC|BLOCK_LEAF );
  assert( idx>=2 && idx<SQLITE_PAGE_SIZE/sizeof(u32)-4 );
  entrySize = SWB(aPage[idx]);
  assert( entrySize>=6 && idx+entrySize<=SQLITE_PAGE_SIZE/sizeof(u32) );
  sqliteDbClearEntry(pCur->pDb, &aPage[idx]);
  to = idx;
  from = idx + entrySize;
  while( from<SQLITE_PAGE_SIZE/sizeof(u32) ){
    int k;
    entrySize = SWB(aPage[from]);
    if( entrySize<=0 ) break;
    for(k=0; k<entrySize; k++){
      aPage[to++] = aPage[from++]
    }
  }
  aPage[to] = 0;

  /*  Decrement the entry count for this table.
  */
  pCur->aLevel[0].aPage[1] = SWB(SWB(pCur->aLevel[0].aPage[1])-1);
  sqlitePgTouch(pCur->aLevel[0].aPage);

  /* If there are more entries on this leaf or this leaf is the root
  ** of the table,  then we are done.
  */
  if( to>2 || pCur->nLevel==1 ) return SQLITE_OK;

  /* Collapse the tree into a more compact form.
  */
  sqliteDbResetCursor(pCur, pCur->nLevel-1);

  i = pCur->nLevel-1;
  assert( i>=0 && i<MAX_LEVEL );
  idx = pCur->aLevel[i].idx;
  aPage = pCur->aLevel[i].aPage;
  assert( SWB(aPage[0])==BLOCK_MAGIC|BLOCK_INDEX );
  assert( idx>=3 && idx<SQLITE_PAGE_SIZE/sizeof(u32) );
  n = SWB(aPage[2]);
  assert( n>=2 && n<=SQLITE_PAGE_SIZE/2*sizeof(u32)-2 );
  sqliteDbDropPage(pCur->pDb, SWB(aPage[idx+1]);
  to = idx;
  from = idx+2;
  limit = n*2 + 3;
  while( from<limit ){
    aPage[to++] = aPage[from++];
  }
  n--;
  if( n==1 ){
    u32 oldPgno, *oldPage;
    oldPgno = SWB(aPage[4]);
    rc = sqlitePgGet(pCur->pDb->pPgr, oldPgno, &oldPage);
    if( rc!=SQLITE_OK ){
      return rc;  /* Do something smarter here */
    }
    memcpy(aPage, oldPage, SQLITE_PAGE_SIZE);
    oldPage[0] = SWB(BLOCK_MAGIC|BLOCK_OVERFLOW);
    oldPage[1] = 0;
    sqliteDbDropPage(pCur->pDb, oldPgno);
    sqlitePgUnref(oldPage);
  }else{
    aPage[2] = SWB(n);
  }
  sqlitePgTouch(aPage);
  return SQLITE_OK;
}

/*
** Copyright (c) 2001 D. Richard Hipp
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the GNU General Public
** License as published by the Free Software Foundation; either
** version 2 of the License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
** General Public License for more details.
** 
** You should have received a copy of the GNU General Public
** License along with this library; if not, write to the
** Free Software Foundation, Inc., 59 Temple Place - Suite 330,
** Boston, MA  02111-1307, USA.
**
** Author contact information:
**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*************************************************************************
** $Id: db.h,v 1.1 2001/02/11 16:56:24 drh Exp $
*/

typedef struct Db Db;
typedef struct DbCursor DbCursor;

int sqliteDbOpen(const char *filename, Db**);
int sqliteDbClose(Db*);
int sqliteDbBeginTransaction(Db*);
int sqliteDbCommit(Db*);
int sqliteDbRollback(Db*);

int sqliteDbCreateTable(Db*, int *pTblno);
int sqliteDbDropTable(Db*, int tblno);

int sqliteDbCursorOpen(Db*, int tblno, DbCursor**);
int sqliteDbCursorClose(DbCursor*);

int sqliteDbCursorFirst(DbCursor*);
int sqliteDbCursorNext(DbCursor*);
int sqliteDbCursorDatasize(DbCursor*);
int sqliteDbCursorKeysize(DbCursor*);
int sqliteDbCursorRead(DbCursor*, int amt, int offset, void *buf);
int sqliteDbCursorReadKey(DbCursor*, int amt, int offset, void *buf);
int sqliteDbCursorWrite(DbCursor*, int amt, int offset, const void *buf);

int sqliteDbCursorFind(DbCursor*, int nKey, const void *pKey, int createFlag);
int sqliteDbCursorResize(DbCursor*, int nData);

/*
** Copyright (c) 2000 D. Richard Hipp
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the GNU General Public
** License as published by the Free Software Foundation; either
** version 2 of the License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
** General Public License for more details.
** 
** You should have received a copy of the GNU General Public
** License along with this library; if not, write to the
** Free Software Foundation, Inc., 59 Temple Place - Suite 330,
** Boston, MA  02111-1307, USA.
**
** Author contact information:
**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*************************************************************************
** This file contains code to implement the database backend (DBBE)
** for sqlite.  The database backend is the interface between
** sqlite and the code that does the actually reading and writing
** of information to the disk.
**
** This file uses Berkeley Database version 1.85 as the database backend.
**
** $Id: dbbebdb1.c,v 1.1 2001/02/11 16:56:24 drh Exp $
*/
#ifdef USE_BDB2

#include "sqliteInt.h"
#include <sys/types.h>
#include <limits.h>
#include <db.h>
#include <sys/stat.h>
#include <unistd.h>
#include <ctype.h>
#include <time.h>

/*
** Information about each open disk file is an instance of this 
** structure.  There will only be one such structure for each
** disk file.  If the VDBE opens the same file twice (as will happen
** for a self-join, for example) then two DbbeCursor structures are
** created but there is only a single BeFile structure with an
** nRef of 2.
*/
typedef struct BeFile BeFile;
struct BeFile {
  char *zName;            /* Name of the file */
  DB dbf;                 /* The file itself */
  int nRef;               /* Number of references */
  int delOnClose;         /* Delete when closing */
  int writeable;          /* Opened for writing */
  DbbeCursor *pCursor; /* Which of several DbbeCursors has the file cursor */
  BeFile *pNext, *pPrev;  /* Next and previous on list of open files */
};

/*
** The following structure contains all information used by BDB2
** database driver.  This is a subclass of the Dbbe structure.
*/
typedef struct Dbbex Dbbex;
struct Dbbex {
  Dbbe dbbe;         /* The base class */
  int write;         /* True for write permission */
  BeFile *pOpen;     /* List of open files */
  char *zDir;        /* Directory hold the database */
};

/*
** An cursor into a database file is an instance of the following structure.
** There can only be a single BeFile structure for each disk file, but
** there can be multiple DbbeCursor structures.  Each DbbeCursor represents
** a cursor pointing to a particular part of the open BeFile.  The
** BeFile.nRef field hold a count of the number of DbbeCursor structures
** associated with the same disk file.
*/
struct DbbeCursor {
  Dbbex *pBe;        /* The database of which this record is a part */
  BeFile *pFile;     /* The database file for this table */
  DBT key;           /* Most recently used key */
  DBT data;          /* Most recent data */
  int needRewind;    /* Next key should be the first */
  int readPending;   /* The fetch hasn't actually been done yet */
};

/*
** The "mkdir()" function only takes one argument under Windows.
*/
#if OS_WIN
# define mkdir(A,B) mkdir(A)
#endif

/*
** Forward declaration
*/
static void sqliteBdb1CloseCursor(DbbeCursor *pCursr);

/*
** Completely shutdown the given database.  Close all files.  Free all memory.
*/
static void sqliteBdb1Close(Dbbe *pDbbe){
  Dbbex *pBe = (Dbbex*)pDbbe;
  BeFile *pFile, *pNext;
  for(pFile=pBe->pOpen; pFile; pFile=pNext){
    pNext = pFile->pNext;
    (*pFile->dbf)(pFile->dbf);
    memset(pFile, 0, sizeof(*pFile));   
    sqliteFree(pFile);
  }
  sqliteDbbeCloseAllTempFiles(pDbbe);
  memset(pBe, 0, sizeof(*pBe));
  sqliteFree(pBe);
}

/*
** Translate the name of an SQL table (or index) into the name 
** of a file that holds the key/data pairs for that table or
** index.  Space to hold the filename is obtained from
** sqliteMalloc() and must be freed by the calling function.
*/
static char *sqliteFileOfTable(Dbbex *pBe, const char *zTable){
  return sqliteDbbeNameToFile(pBe->zDir, zTable, ".tbl");
}

/*
** Open a new table cursor.  Write a pointer to the corresponding
** DbbeCursor structure into *ppCursr.  Return an integer success
** code:
**
**    SQLITE_OK          It worked!
**
**    SQLITE_NOMEM       sqliteMalloc() failed
**
**    SQLITE_PERM        Attempt to access a file for which file
**                       access permission is denied
**
**    SQLITE_BUSY        Another thread or process is already using
**                       the corresponding file and has that file locked.
**
**    SQLITE_READONLY    The current thread already has this file open
**                       readonly but you are trying to open for writing.
**                       (This can happen if a SELECT callback tries to
**                       do an UPDATE or DELETE.)
**
** If zTable is 0 or "", then a temporary database file is created and
** a cursor to that temporary file is opened.  The temporary file
** will be deleted from the disk when it is closed.
*/
static int sqliteBdb1OpenCursor(
  Dbbe *pDbbe,            /* The database the table belongs to */
  const char *zTable,     /* The SQL name of the file to be opened */
  int writeable,          /* True to open for writing */
  int intKeyOnly,         /* True if only integer keys are used */
  DbbeCursor **ppCursr    /* Write the resulting table pointer here */
){
  char *zFile;            /* Name of the table file */
  DbbeCursor *pCursr;     /* The new table cursor */
  BeFile *pFile;          /* The underlying data file for this table */
  int rc = SQLITE_OK;     /* Return value */
  int open_flags;         /* Flags passed to dbopen() */
  Dbbex *pBe = (Dbbex*)pDbbe;

  *ppCursr = 0;
  pCursr = sqliteMalloc( sizeof(*pCursr) );
  if( pCursr==0 ) return SQLITE_NOMEM;
  if( zTable ){
    zFile = sqliteFileOfTable(pBe, zTable);
    for(pFile=pBe->pOpen; pFile; pFile=pFile->pNext){
      if( strcmp(pFile->zName,zFile)==0 ) break;
    }
  }else{
    pFile = 0;
    zFile = 0;
  }
  if( pFile==0 ){
    if( writeable ){
      open_flags = O_RDWR|O_CREAT
    }else{
      open_flags = O_RDONLY;
    }
    pFile = sqliteMalloc( sizeof(*pFile) );
    if( pFile==0 ){
      sqliteFree(zFile);
      return SQLITE_NOMEM;
    }
    if( zFile ){
      if( !writeable || pBe->write ){
        pFile->dbf = dbopen(zFile, open_flags, DB_HASH, 0);
      }else{
        pFile->dbf = 0;
      }
    }else{
      int limit;
      char zRandom[50];
      zFile = 0;
      limit = 5;
      do {
        sqliteRandomName(zRandom, "_temp_table_");
        sqliteFree(zFile);
        zFile = sqliteFileOfTable(pBe, zRandom);
        pFile->dbf = dbopen(zFile, open_flags, DB_HASH, 0);
      }while( pFile->dbf==0 && limit-- >= 0);
      pFile->delOnClose = 1;
    }
    pFile->writeable = writeable;
    pFile->zName = zFile;
    pFile->nRef = 1;
    pFile->pPrev = 0;
    if( pBe->pOpen ){
      pBe->pOpen->pPrev = pFile;
    }
    pFile->pCursor = 0;
    pFile->pNext = pBe->pOpen;
    pBe->pOpen = pFile;
    if( pFile->dbf==0 ){
      if( !writeable && access(zFile,0) ){
        /* Trying to read a non-existant file.  This is OK.  All the
        ** reads will return empty, which is what we want. */
        rc = SQLITE_OK;   
      }else if( pBe->write==0 ){
        rc = SQLITE_READONLY;
      }else if( access(zFile,W_OK|R_OK) ){
        rc = SQLITE_PERM;
      }else{
        rc = SQLITE_BUSY;
      }
    }
  }else{
    sqliteFree(zFile);
    pFile->nRef++;
    if( writeable && !pFile->writeable ){
      rc = SQLITE_READONLY;
    }
  }
  pCursr->pBe = pBe;
  pCursr->pFile = pFile;
  pCursr->readPending = 0;
  pCursr->needRewind = 1;
  if( rc!=SQLITE_OK ){
    sqliteBdb1CloseCursor(pCursr);
    *ppCursr = 0;
  }else{
    *ppCursr = pCursr;
  }
  return rc;
}

/*
** Drop a table from the database.  The file on the disk that corresponds
** to this table is deleted.
*/
static void sqliteBdb1DropTable(Dbbe *pBe, const char *zTable){
  char *zFile;            /* Name of the table file */

  zFile = sqliteFileOfTable((Dbbex*)pBe, zTable);
  unlink(zFile);
  sqliteFree(zFile);
}

/*
** Close a cursor previously opened by sqliteBdb1OpenCursor().
**
** There can be multiple cursors pointing to the same open file.
** The underlying file is not closed until all cursors have been
** closed.  This routine decrements the BeFile.nref field of the
** underlying file and closes the file when nref reaches 0.
*/
static void sqliteBdb1CloseCursor(DbbeCursor *pCursr){
  BeFile *pFile;
  Dbbex *pBe;
  if( pCursr==0 ) return;
  pFile = pCursr->pFile;
  pBe = pCursr->pBe;
  if( pFile->pCursor==pCursr ){
    pFile->pCursor = 0;
  }
  pFile->nRef--;
  if( pFile->dbf!=NULL ){
    (*pFile->dbf->sync)(pFile->dbf, 0);
  }
  if( pFile->nRef<=0 ){
    if( pFile->dbf!=NULL ){
      (*pFile->dbf->close)(pFile->dbf);
    }
    if( pFile->pPrev ){
      pFile->pPrev->pNext = pFile->pNext;
    }else{
      pBe->pOpen = pFile->pNext;
    }
    if( pFile->pNext ){
      pFile->pNext->pPrev = pFile->pPrev;
    }
    if( pFile->delOnClose ){
      unlink(pFile->zName);
    }
    sqliteFree(pFile->zName);
    memset(pFile, 0, sizeof(*pFile));
    sqliteFree(pFile);
  }
  if( pCursr->key.dptr ) free(pCursr->key.dptr); ######
  if( pCursr->data.dptr ) free(pCursr->data.dptr); ######
  memset(pCursr, 0, sizeof(*pCursr));
  sqliteFree(pCursr);
}

/*
** Reorganize a table to reduce search times and disk usage.
*/
static int sqliteBdb1ReorganizeTable(Dbbe *pBe, const char *zTable){
  /* No-op */
  return SQLITE_OK;
}

/*
** Clear the given datum
*/
static void datumClear(datum *p){
  if( p->dptr ) free(p->dptr); ########
  p->data = 0;
  p->size = 0;
}

/*
** Fetch a single record from an open cursor.  Return 1 on success
** and 0 on failure.
*/
static int sqliteBdb1Fetch(DbbeCursor *pCursr, int nKey, char *pKey){
  DBT key;
  key.size = nKey;
  key.data = pKey;
  datumClear(&pCursr->key);
  datumClear(&pCursr->data);
  if( pCursr->pFile && pCursr->pFile->dbf ){
    pCursr->data = gdbm_fetch(pCursr->pFile->dbf, key);
  }
  return pCursr->data.dptr!=0;
}

/*
** Return 1 if the given key is already in the table.  Return 0
** if it is not.
*/
static int sqliteBdb1Test(DbbeCursor *pCursr, int nKey, char *pKey){
  DBT key;
  int result = 0;
  key.dsize = nKey;
  key.dptr = pKey;
  if( pCursr->pFile && pCursr->pFile->dbf ){
    result = gdbm_exists(pCursr->pFile->dbf, key);
  }
  return result;
}

/*
** Copy bytes from the current key or data into a buffer supplied by
** the calling function.  Return the number of bytes copied.
*/
static
int sqliteBdb1CopyKey(DbbeCursor *pCursr, int offset, int size, char *zBuf){
  int n;
  if( offset>=pCursr->key.dsize ) return 0;
  if( offset+size>pCursr->key.dsize ){
    n = pCursr->key.dsize - offset;
  }else{
    n = size;
  }
  memcpy(zBuf, &pCursr->key.dptr[offset], n);
  return n;
}
static
int sqliteBdb1CopyData(DbbeCursor *pCursr, int offset, int size, char *zBuf){
  int n;
  if( pCursr->readPending && pCursr->pFile && pCursr->pFile->dbf ){
    pCursr->data = gdbm_fetch(pCursr->pFile->dbf, pCursr->key);
    pCursr->readPending = 0;
  }
  if( offset>=pCursr->data.dsize ) return 0;
  if( offset+size>pCursr->data.dsize ){
    n = pCursr->data.dsize - offset;
  }else{
    n = size;
  }
  memcpy(zBuf, &pCursr->data.dptr[offset], n);
  return n;
}

/*
** Return a pointer to bytes from the key or data.  The data returned
** is ephemeral.
*/
static char *sqliteBdb1ReadKey(DbbeCursor *pCursr, int offset){
  if( offset<0 || offset>=pCursr->key.dsize ) return "";
  return &pCursr->key.dptr[offset];
}
static char *sqliteBdb1ReadData(DbbeCursor *pCursr, int offset){
  if( pCursr->readPending && pCursr->pFile && pCursr->pFile->dbf ){
    pCursr->data = gdbm_fetch(pCursr->pFile->dbf, pCursr->key);
    pCursr->readPending = 0;
  }
  if( offset<0 || offset>=pCursr->data.dsize ) return "";
  return &pCursr->data.dptr[offset];
}

/*
** Return the total number of bytes in either data or key.
*/
static int sqliteBdb1KeyLength(DbbeCursor *pCursr){
  return pCursr->key.dsize;
}
static int sqliteBdb1DataLength(DbbeCursor *pCursr){
  if( pCursr->readPending && pCursr->pFile && pCursr->pFile->dbf ){
    pCursr->data = gdbm_fetch(pCursr->pFile->dbf, pCursr->key);
    pCursr->readPending = 0;
  }
  return pCursr->data.dsize;
}

/*
** Make is so that the next call to sqliteNextKey() finds the first
** key of the table.
*/
static int sqliteBdb1Rewind(DbbeCursor *pCursr){
  pCursr->needRewind = 1;
  return SQLITE_OK;
}

/*
** Read the next key from the table.  Return 1 on success.  Return
** 0 if there are no more keys.
*/
static int sqliteBdb1NextKey(DbbeCursor *pCursr){
  DBT nextkey;
  int rc;
  if( pCursr==0 || pCursr->pFile==0 || pCursr->pFile->dbf==0 ){
    pCursr->readPending = 0;
    return 0;
  }
  if( pCursr->needRewind ){
    nextkey = gdbm_firstkey(pCursr->pFile->dbf);
    pCursr->needRewind = 0;
  }else{
    nextkey = gdbm_nextkey(pCursr->pFile->dbf, pCursr->key);
  }
  datumClear(&pCursr->key);
  datumClear(&pCursr->data);
  pCursr->key = nextkey;
  if( pCursr->key.dptr ){
    pCursr->readPending = 1;
    rc = 1;
  }else{
    pCursr->needRewind = 1;
    pCursr->readPending = 0;
    rc = 0;
  }
  return rc;
}

/*
** Get a new integer key.
*/
static int sqliteBdb1New(DbbeCursor *pCursr){
  int iKey;
  DBT key;
  int go = 1;

  if( pCursr->pFile==0 || pCursr->pFile->dbf==0 ) return 1;
  while( go ){
    iKey = sqliteRandomInteger();
    if( iKey==0 ) continue;
    key.dptr = (char*)&iKey;
    key.dsize = 4;
    go = gdbm_exists(pCursr->pFile->dbf, key);
  }
  return iKey;
}   

/*
** Write an entry into the table.  Overwrite any prior entry with the
** same key.
*/
static int sqliteBdb1Put(
  DbbeCursor *pCursr,  /* Write to the database associated with this cursor */
  int nKey,            /* Number of bytes in the key */
  char *pKey,          /* The data for the key */
  int nData,           /* Number of bytes of data */
  char *pData          /* The data */
){
  DBT data, key;
  int rc;
  if( pCursr->pFile==0 || pCursr->pFile->dbf==0 ) return SQLITE_ERROR;
  data.dsize = nData;
  data.dptr = pData;
  key.dsize = nKey;
  key.dptr = pKey;
  rc = gdbm_store(pCursr->pFile->dbf, key, data, GDBM_REPLACE);
  if( rc ) rc = SQLITE_ERROR;
  datumClear(&pCursr->key);
  datumClear(&pCursr->data);
  return rc;
}

/*
** Remove an entry from a table, if the entry exists.
*/
static int sqliteBdb1Delete(DbbeCursor *pCursr, int nKey, char *pKey){
  DBT key;
  int rc;
  datumClear(&pCursr->key);
  datumClear(&pCursr->data);
  if( pCursr->pFile==0 || pCursr->pFile->dbf==0 ) return SQLITE_ERROR;
  key.dsize = nKey;
  key.dptr = pKey;
  rc = gdbm_delete(pCursr->pFile->dbf, key);
  if( rc ) rc = SQLITE_ERROR;
  return rc;
}

/*
** Open a temporary file.  The file is located in the same directory
** as the rest of the database.
*/
static int sqliteBdb1OpenTempFile(Dbbe *pDbbe, FILE **ppFile){
  Dbbex *pBe = (Dbbex*)pDbbe;
  return sqliteDbbeOpenTempFile(pBe->zDir, pDbbe, ppFile);
}

/*
** This variable contains pointers to all of the access methods
** used to implement the GDBM backend.
*/
static struct DbbeMethods gdbmMethods = {
  /* n         Close */   sqliteBdb1Close,
  /*      OpenCursor */   sqliteBdb1OpenCursor,
  /*       DropTable */   sqliteBdb1DropTable,
  /* ReorganizeTable */   sqliteBdb1ReorganizeTable,
  /*     CloseCursor */   sqliteBdb1CloseCursor,
  /*           Fetch */   sqliteBdb1Fetch,
  /*            Test */   sqliteBdb1Test,
  /*         CopyKey */   sqliteBdb1CopyKey,
  /*        CopyData */   sqliteBdb1CopyData,
  /*         ReadKey */   sqliteBdb1ReadKey,
  /*        ReadData */   sqliteBdb1ReadData,
  /*       KeyLength */   sqliteBdb1KeyLength,
  /*      DataLength */   sqliteBdb1DataLength,
  /*         NextKey */   sqliteBdb1NextKey,
  /*          Rewind */   sqliteBdb1Rewind,
  /*             New */   sqliteBdb1New,
  /*             Put */   sqliteBdb1Put,
  /*          Delete */   sqliteBdb1Delete,
  /*    OpenTempFile */   sqliteBdb1OpenTempFile,
  /*   CloseTempFile */   sqliteDbbeCloseTempFile
};


/*
** This routine opens a new database.  For the GDBM driver
** implemented here, the database name is the name of the directory
** containing all the files of the database.
**
** If successful, a pointer to the Dbbe structure is returned.
** If there are errors, an appropriate error message is left
** in *pzErrMsg and NULL is returned.
*/
Dbbe *sqliteBdb1Open(
  const char *zName,     /* The name of the database */
  int writeFlag,         /* True if we will be writing to the database */
  int createFlag,        /* True to create database if it doesn't exist */
  char **pzErrMsg        /* Write error messages (if any) here */
){
  Dbbex *pNew;
  struct stat statbuf;
  char *zMaster;

  if( !writeFlag ) createFlag = 0;
  if( stat(zName, &statbuf)!=0 ){
    if( createFlag ) mkdir(zName, 0750);
    if( stat(zName, &statbuf)!=0 ){
      sqliteSetString(pzErrMsg, createFlag ? 
         "can't find or create directory \"" : "can't find directory \"",
         zName, "\"", 0);
      return 0;
    }
  }
  if( !S_ISDIR(statbuf.st_mode) ){
    sqliteSetString(pzErrMsg, "not a directory: \"", zName, "\"", 0);
    return 0;
  }
  if( access(zName, writeFlag ? (X_OK|W_OK|R_OK) : (X_OK|R_OK)) ){
    sqliteSetString(pzErrMsg, "access permission denied", 0);
    return 0;
  }
  zMaster = 0;
  sqliteSetString(&zMaster, zName, "/" MASTER_NAME ".tbl", 0);
  if( stat(zMaster, &statbuf)==0
   && access(zMaster, writeFlag ? (W_OK|R_OK) : R_OK)!=0 ){
    sqliteSetString(pzErrMsg, "access permission denied for ", zMaster, 0);
    sqliteFree(zMaster);
    return 0;
  }
  sqliteFree(zMaster);
  pNew = sqliteMalloc(sizeof(Dbbex) + strlen(zName) + 1);
  if( pNew==0 ){
    sqliteSetString(pzErrMsg, "out of memory", 0);
    return 0;
  }
  pNew->dbbe.x = &gdbmMethods;
  pNew->zDir = (char*)&pNew[1];
  strcpy(pNew->zDir, zName);
  pNew->write = writeFlag;
  pNew->pOpen = 0;
  return &pNew->dbbe;
}

/*
** Copyright (c) 2000 D. Richard Hipp
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the GNU General Public
** License as published by the Free Software Foundation; either
** version 2 of the License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
** General Public License for more details.
** 
** You should have received a copy of the GNU General Public
** License along with this library; if not, write to the
** Free Software Foundation, Inc., 59 Temple Place - Suite 330,
** Boston, MA  02111-1307, USA.
**
** Author contact information:
**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*************************************************************************
** This file contains code to implement the database backend (DBBE)
** for sqlite.  The database backend is the interface between
** sqlite and the code that does the actually reading and writing
** of information to the disk.
**
** This file uses GDBM as the database backend.  It should be
** relatively simple to convert to a different database such
** as NDBM, SDBM, or BerkeleyDB.
**
** $Id: dbbemird.c,v 1.1 2001/02/11 16:56:24 drh Exp $
*/
#include "sqliteInt.h"
#include <gdbm.h>
#include <sys/stat.h>
#include <unistd.h>
#include <ctype.h>
#include <time.h>

/*
** Information about each open disk file is an instance of this 
** structure.  There will only be one such structure for each
** disk file.  If the VDBE opens the same file twice (as will happen
** for a self-join, for example) then two DbbeCursor structures are
** created but there is only a single BeFile structure with an
** nRef of 2.
*/
typedef struct BeFile BeFile;
struct BeFile {
  char *zName;            /* Name of the file */
  GDBM_FILE dbf;          /* The file itself */
  int nRef;               /* Number of references */
  int delOnClose;         /* Delete when closing */
  int writeable;          /* Opened for writing */
  BeFile *pNext, *pPrev;  /* Next and previous on list of open files */
};

/*
** The following structure holds the current state of the RC4 algorithm.
** We use RC4 as a random number generator.  Each call to RC4 gives
** a random 8-bit number.
**
** Nothing in this file or anywhere else in SQLite does any kind of
** encryption.  The RC4 algorithm is being used as a PRNG (pseudo-random
** number generator) not as an encryption device.
*/
struct rc4 {
  int i, j;
  int s[256];
};

/*
** The following structure contains all information used by GDBM
** database driver.  This is a subclass of the Dbbe structure.
*/
typedef struct Dbbex Dbbex;
struct Dbbex {
  Dbbe dbbe;         /* The base class */
  char *zDir;        /* The directory containing the database */
  int write;         /* True for write permission */
  BeFile *pOpen;     /* List of open files */
  int nTemp;         /* Number of temporary files created */
  FILE **apTemp;     /* Space to hold temporary file pointers */
  char **azTemp;     /* Names of the temporary files */
  struct rc4 rc4;    /* The random number generator */
};

/*
** An cursor into a database file is an instance of the following structure.
** There can only be a single BeFile structure for each disk file, but
** there can be multiple DbbeCursor structures.  Each DbbeCursor represents
** a cursor pointing to a particular part of the open BeFile.  The
** BeFile.nRef field hold a count of the number of DbbeCursor structures
** associated with the same disk file.
*/
struct DbbeCursor {
  Dbbex *pBe;        /* The database of which this record is a part */
  BeFile *pFile;     /* The database file for this table */
  datum key;         /* Most recently used key */
  datum data;        /* Most recent data */
  int needRewind;    /* Next key should be the first */
  int readPending;   /* The fetch hasn't actually been done yet */
};

/*
** Initialize the RC4 PRNG.  "seed" is a pointer to some random
** data used to initialize the PRNG.  
*/
static void rc4init(struct rc4 *p, char *seed, int seedlen){
  int i;
  char k[256];
  p->j = 0;
  p->i = 0;
  for(i=0; i<256; i++){
    p->s[i] = i;
    k[i] = seed[i%seedlen];
  }
  for(i=0; i<256; i++){
    int t;
    p->j = (p->j + p->s[i] + k[i]) & 0xff;
    t = p->s[p->j];
    p->s[p->j] = p->s[i];
    p->s[i] = t;
  }
}

/*
** Get a single 8-bit random value from the RC4 PRNG.
*/
static int rc4byte(struct rc4 *p){
  int t;
  p->i = (p->i + 1) & 0xff;
  p->j = (p->j + p->s[p->i]) & 0xff;
  t = p->s[p->i];
  p->s[p->i] = p->s[p->j];
  p->s[p->j] = t;
  t = p->s[p->i] + p->s[p->j];
  return t & 0xff;
}

/*
** The "mkdir()" function only takes one argument under Windows.
*/
#if OS_WIN
# define mkdir(A,B) mkdir(A)
#endif

/*
** Forward declaration
*/
static void sqliteGdbmCloseCursor(DbbeCursor *pCursr);

/*
** Completely shutdown the given database.  Close all files.  Free all memory.
*/
static void sqliteGdbmClose(Dbbe *pDbbe){
  Dbbex *pBe = (Dbbex*)pDbbe;
  BeFile *pFile, *pNext;
  int i;
  for(pFile=pBe->pOpen; pFile; pFile=pNext){
    pNext = pFile->pNext;
    gdbm_close(pFile->dbf);
    memset(pFile, 0, sizeof(*pFile));   
    sqliteFree(pFile);
  }
  for(i=0; i<pBe->nTemp; i++){
    if( pBe->apTemp[i]!=0 ){
      unlink(pBe->azTemp[i]);
      fclose(pBe->apTemp[i]);
      sqliteFree(pBe->azTemp[i]);
      pBe->apTemp[i] = 0;
      pBe->azTemp[i] = 0;
      break;
    }
  }
  sqliteFree(pBe->azTemp);
  sqliteFree(pBe->apTemp);
  memset(pBe, 0, sizeof(*pBe));
  sqliteFree(pBe);
}

/*
** Translate the name of an SQL table (or index) into the name 
** of a file that holds the key/data pairs for that table or
** index.  Space to hold the filename is obtained from
** sqliteMalloc() and must be freed by the calling function.
*/
static char *sqliteFileOfTable(Dbbex *pBe, const char *zTable){
  char *zFile = 0;
  int i;
  sqliteSetString(&zFile, pBe->zDir, "/", zTable, ".tbl", 0);
  if( zFile==0 ) return 0;
  for(i=strlen(pBe->zDir)+1; zFile[i]; i++){
    int c = zFile[i];
    if( isupper(c) ){
      zFile[i] = tolower(c);
    }else if( !isalnum(c) && c!='-' && c!='_' && c!='.' ){
      zFile[i] = '+';
    }
  }
  return zFile;
}

/*
** Generate a random filename with the given prefix.  The new filename
** is written into zBuf[].  The calling function must insure that
** zBuf[] is big enough to hold the prefix plus 20 or so extra
** characters.
**
** Very random names are chosen so that the chance of a
** collision with an existing filename is very very small.
*/
static void randomName(struct rc4 *pRc4, char *zBuf, char *zPrefix){
  int i, j;
  static const char zRandomChars[] = "abcdefghijklmnopqrstuvwxyz0123456789";
  strcpy(zBuf, zPrefix);
  j = strlen(zBuf);
  for(i=0; i<15; i++){
    int c = rc4byte(pRc4) % (sizeof(zRandomChars) - 1);
    zBuf[j++] = zRandomChars[c];
  }
  zBuf[j] = 0;
}

/*
** Open a new table cursor.  Write a pointer to the corresponding
** DbbeCursor structure into *ppCursr.  Return an integer success
** code:
**
**    SQLITE_OK          It worked!
**
**    SQLITE_NOMEM       sqliteMalloc() failed
**
**    SQLITE_PERM        Attempt to access a file for which file
**                       access permission is denied
**
**    SQLITE_BUSY        Another thread or process is already using
**                       the corresponding file and has that file locked.
**
**    SQLITE_READONLY    The current thread already has this file open
**                       readonly but you are trying to open for writing.
**                       (This can happen if a SELECT callback tries to
**                       do an UPDATE or DELETE.)
**
** If zTable is 0 or "", then a temporary database file is created and
** a cursor to that temporary file is opened.  The temporary file
** will be deleted from the disk when it is closed.
*/
static int sqliteGdbmOpenCursor(
  Dbbe *pDbbe,            /* The database the table belongs to */
  const char *zTable,     /* The SQL name of the file to be opened */
  int writeable,          /* True to open for writing */
  DbbeCursor **ppCursr    /* Write the resulting table pointer here */
){
  char *zFile;            /* Name of the table file */
  DbbeCursor *pCursr;     /* The new table cursor */
  BeFile *pFile;          /* The underlying data file for this table */
  int rc = SQLITE_OK;     /* Return value */
  int rw_mask;            /* Permissions mask for opening a table */
  int mode;               /* Mode for opening a table */
  Dbbex *pBe = (Dbbex*)pDbbe;

  *ppCursr = 0;
  pCursr = sqliteMalloc( sizeof(*pCursr) );
  if( pCursr==0 ) return SQLITE_NOMEM;
  if( zTable ){
    zFile = sqliteFileOfTable(pBe, zTable);
    for(pFile=pBe->pOpen; pFile; pFile=pFile->pNext){
      if( strcmp(pFile->zName,zFile)==0 ) break;
    }
  }else{
    pFile = 0;
    zFile = 0;
  }
  if( pFile==0 ){
    if( writeable ){
      rw_mask = GDBM_WRCREAT | GDBM_FAST;
      mode = 0640;
    }else{
      rw_mask = GDBM_READER;
      mode = 0640;
    }
    pFile = sqliteMalloc( sizeof(*pFile) );
    if( pFile==0 ){
      sqliteFree(zFile);
      return SQLITE_NOMEM;
    }
    if( zFile ){
      if( !writeable || pBe->write ){
        pFile->dbf = gdbm_open(zFile, 0, rw_mask, mode, 0);
      }else{
        pFile->dbf = 0;
      }
    }else{
      int limit;
      struct rc4 *pRc4;
      char zRandom[50];
      pRc4 = &pBe->rc4;
      zFile = 0;
      limit = 5;
      do {
        randomName(&pBe->rc4, zRandom, "_temp_table_");
        sqliteFree(zFile);
        zFile = sqliteFileOfTable(pBe, zRandom);
        pFile->dbf = gdbm_open(zFile, 0, rw_mask, mode, 0);
      }while( pFile->dbf==0 && limit-- >= 0);
      pFile->delOnClose = 1;
    }
    pFile->writeable = writeable;
    pFile->zName = zFile;
    pFile->nRef = 1;
    pFile->pPrev = 0;
    if( pBe->pOpen ){
      pBe->pOpen->pPrev = pFile;
    }
    pFile->pNext = pBe->pOpen;
    pBe->pOpen = pFile;
    if( pFile->dbf==0 ){
      if( !writeable && access(zFile,0) ){
        /* Trying to read a non-existant file.  This is OK.  All the
        ** reads will return empty, which is what we want. */
        rc = SQLITE_OK;   
      }else if( pBe->write==0 ){
        rc = SQLITE_READONLY;
      }else if( access(zFile,W_OK|R_OK) ){
        rc = SQLITE_PERM;
      }else{
        rc = SQLITE_BUSY;
      }
    }
  }else{
    sqliteFree(zFile);
    pFile->nRef++;
    if( writeable && !pFile->writeable ){
      rc = SQLITE_READONLY;
    }
  }
  pCursr->pBe = pBe;
  pCursr->pFile = pFile;
  pCursr->readPending = 0;
  pCursr->needRewind = 1;
  if( rc!=SQLITE_OK ){
    sqliteGdbmCloseCursor(pCursr);
    *ppCursr = 0;
  }else{
    *ppCursr = pCursr;
  }
  return rc;
}

/*
** Drop a table from the database.  The file on the disk that corresponds
** to this table is deleted.
*/
static void sqliteGdbmDropTable(Dbbe *pBe, const char *zTable){
  char *zFile;            /* Name of the table file */

  zFile = sqliteFileOfTable((Dbbex*)pBe, zTable);
  unlink(zFile);
  sqliteFree(zFile);
}

/*
** Close a cursor previously opened by sqliteGdbmOpenCursor().
**
** There can be multiple cursors pointing to the same open file.
** The underlying file is not closed until all cursors have been
** closed.  This routine decrements the BeFile.nref field of the
** underlying file and closes the file when nref reaches 0.
*/
static void sqliteGdbmCloseCursor(DbbeCursor *pCursr){
  BeFile *pFile;
  Dbbex *pBe;
  if( pCursr==0 ) return;
  pFile = pCursr->pFile;
  pBe = pCursr->pBe;
  pFile->nRef--;
  if( pFile->dbf!=NULL ){
    gdbm_sync(pFile->dbf);
  }
  if( pFile->nRef<=0 ){
    if( pFile->dbf!=NULL ){
      gdbm_close(pFile->dbf);
    }
    if( pFile->pPrev ){
      pFile->pPrev->pNext = pFile->pNext;
    }else{
      pBe->pOpen = pFile->pNext;
    }
    if( pFile->pNext ){
      pFile->pNext->pPrev = pFile->pPrev;
    }
    if( pFile->delOnClose ){
      unlink(pFile->zName);
    }
    sqliteFree(pFile->zName);
    memset(pFile, 0, sizeof(*pFile));
    sqliteFree(pFile);
  }
  if( pCursr->key.dptr ) free(pCursr->key.dptr);
  if( pCursr->data.dptr ) free(pCursr->data.dptr);
  memset(pCursr, 0, sizeof(*pCursr));
  sqliteFree(pCursr);
}

/*
** Reorganize a table to reduce search times and disk usage.
*/
static int sqliteGdbmReorganizeTable(Dbbe *pBe, const char *zTable){
  DbbeCursor *pCrsr;
  int rc;

  rc = sqliteGdbmOpenCursor(pBe, zTable, 1, &pCrsr);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  if( pCrsr && pCrsr->pFile && pCrsr->pFile->dbf ){
    gdbm_reorganize(pCrsr->pFile->dbf);
  }
  if( pCrsr ){
    sqliteGdbmCloseCursor(pCrsr);
  }
  return SQLITE_OK;
}

/*
** Clear the given datum
*/
static void datumClear(datum *p){
  if( p->dptr ) free(p->dptr);
  p->dptr = 0;
  p->dsize = 0;
}

/*
** Fetch a single record from an open cursor.  Return 1 on success
** and 0 on failure.
*/
static int sqliteGdbmFetch(DbbeCursor *pCursr, int nKey, char *pKey){
  datum key;
  key.dsize = nKey;
  key.dptr = pKey;
  datumClear(&pCursr->key);
  datumClear(&pCursr->data);
  if( pCursr->pFile && pCursr->pFile->dbf ){
    pCursr->data = gdbm_fetch(pCursr->pFile->dbf, key);
  }
  return pCursr->data.dptr!=0;
}

/*
** Return 1 if the given key is already in the table.  Return 0
** if it is not.
*/
static int sqliteGdbmTest(DbbeCursor *pCursr, int nKey, char *pKey){
  datum key;
  int result = 0;
  key.dsize = nKey;
  key.dptr = pKey;
  if( pCursr->pFile && pCursr->pFile->dbf ){
    result = gdbm_exists(pCursr->pFile->dbf, key);
  }
  return result;
}

/*
** Copy bytes from the current key or data into a buffer supplied by
** the calling function.  Return the number of bytes copied.
*/
static
int sqliteGdbmCopyKey(DbbeCursor *pCursr, int offset, int size, char *zBuf){
  int n;
  if( offset>=pCursr->key.dsize ) return 0;
  if( offset+size>pCursr->key.dsize ){
    n = pCursr->key.dsize - offset;
  }else{
    n = size;
  }
  memcpy(zBuf, &pCursr->key.dptr[offset], n);
  return n;
}
static
int sqliteGdbmCopyData(DbbeCursor *pCursr, int offset, int size, char *zBuf){
  int n;
  if( pCursr->readPending && pCursr->pFile && pCursr->pFile->dbf ){
    pCursr->data = gdbm_fetch(pCursr->pFile->dbf, pCursr->key);
    pCursr->readPending = 0;
  }
  if( offset>=pCursr->data.dsize ) return 0;
  if( offset+size>pCursr->data.dsize ){
    n = pCursr->data.dsize - offset;
  }else{
    n = size;
  }
  memcpy(zBuf, &pCursr->data.dptr[offset], n);
  return n;
}

/*
** Return a pointer to bytes from the key or data.  The data returned
** is ephemeral.
*/
static char *sqliteGdbmReadKey(DbbeCursor *pCursr, int offset){
  if( offset<0 || offset>=pCursr->key.dsize ) return "";
  return &pCursr->key.dptr[offset];
}
static char *sqliteGdbmReadData(DbbeCursor *pCursr, int offset){
  if( pCursr->readPending && pCursr->pFile && pCursr->pFile->dbf ){
    pCursr->data = gdbm_fetch(pCursr->pFile->dbf, pCursr->key);
    pCursr->readPending = 0;
  }
  if( offset<0 || offset>=pCursr->data.dsize ) return "";
  return &pCursr->data.dptr[offset];
}

/*
** Return the total number of bytes in either data or key.
*/
static int sqliteGdbmKeyLength(DbbeCursor *pCursr){
  return pCursr->key.dsize;
}
static int sqliteGdbmDataLength(DbbeCursor *pCursr){
  if( pCursr->readPending && pCursr->pFile && pCursr->pFile->dbf ){
    pCursr->data = gdbm_fetch(pCursr->pFile->dbf, pCursr->key);
    pCursr->readPending = 0;
  }
  return pCursr->data.dsize;
}

/*
** Make is so that the next call to sqliteNextKey() finds the first
** key of the table.
*/
static int sqliteGdbmRewind(DbbeCursor *pCursr){
  pCursr->needRewind = 1;
  return SQLITE_OK;
}

/*
** Read the next key from the table.  Return 1 on success.  Return
** 0 if there are no more keys.
*/
static int sqliteGdbmNextKey(DbbeCursor *pCursr){
  datum nextkey;
  int rc;
  if( pCursr==0 || pCursr->pFile==0 || pCursr->pFile->dbf==0 ){
    pCursr->readPending = 0;
    return 0;
  }
  if( pCursr->needRewind ){
    nextkey = gdbm_firstkey(pCursr->pFile->dbf);
    pCursr->needRewind = 0;
  }else{
    nextkey = gdbm_nextkey(pCursr->pFile->dbf, pCursr->key);
  }
  datumClear(&pCursr->key);
  datumClear(&pCursr->data);
  pCursr->key = nextkey;
  if( pCursr->key.dptr ){
    pCursr->readPending = 1;
    rc = 1;
  }else{
    pCursr->needRewind = 1;
    pCursr->readPending = 0;
    rc = 0;
  }
  return rc;
}

/*
** Get a new integer key.
*/
static int sqliteGdbmNew(DbbeCursor *pCursr){
  int iKey;
  datum key;
  int go = 1;
  int i;
  struct rc4 *pRc4;

  if( pCursr->pFile==0 || pCursr->pFile->dbf==0 ) return 1;
  pRc4 = &pCursr->pBe->rc4;
  while( go ){
    iKey = 0;
    for(i=0; i<4; i++){
      iKey = (iKey<<8) + rc4byte(pRc4);
    }
    if( iKey==0 ) continue;
    key.dptr = (char*)&iKey;
    key.dsize = 4;
    go = gdbm_exists(pCursr->pFile->dbf, key);
  }
  return iKey;
}   

/*
** Write an entry into the table.  Overwrite any prior entry with the
** same key.
*/
static int
sqliteGdbmPut(DbbeCursor *pCursr, int nKey,char *pKey,int nData,char *pData){
  datum data, key;
  int rc;
  if( pCursr->pFile==0 || pCursr->pFile->dbf==0 ) return SQLITE_ERROR;
  data.dsize = nData;
  data.dptr = pData;
  key.dsize = nKey;
  key.dptr = pKey;
  rc = gdbm_store(pCursr->pFile->dbf, key, data, GDBM_REPLACE);
  if( rc ) rc = SQLITE_ERROR;
  datumClear(&pCursr->key);
  datumClear(&pCursr->data);
  return rc;
}

/*
** Remove an entry from a table, if the entry exists.
*/
static int sqliteGdbmDelete(DbbeCursor *pCursr, int nKey, char *pKey){
  datum key;
  int rc;
  datumClear(&pCursr->key);
  datumClear(&pCursr->data);
  if( pCursr->pFile==0 || pCursr->pFile->dbf==0 ) return SQLITE_ERROR;
  key.dsize = nKey;
  key.dptr = pKey;
  rc = gdbm_delete(pCursr->pFile->dbf, key);
  if( rc ) rc = SQLITE_ERROR;
  return rc;
}

/*
** Open a temporary file.  The file should be deleted when closed.
**
** Note that we can't use the old Unix trick of opening the file
** and then immediately unlinking the file.  That works great
** under Unix, but fails when we try to port to Windows.
*/
static int sqliteGdbmOpenTempFile(Dbbe *pDbbe, FILE **ppFile){
  char *zFile;         /* Full name of the temporary file */
  char zBuf[50];       /* Base name of the temporary file */
  int i;               /* Loop counter */
  int limit;           /* Prevent an infinite loop */
  int rc = SQLITE_OK;  /* Value returned by this function */
  Dbbex *pBe = (Dbbex*)pDbbe;

  for(i=0; i<pBe->nTemp; i++){
    if( pBe->apTemp[i]==0 ) break;
  }
  if( i>=pBe->nTemp ){
    pBe->nTemp++;
    pBe->apTemp = sqliteRealloc(pBe->apTemp, pBe->nTemp*sizeof(FILE*) );
    pBe->azTemp = sqliteRealloc(pBe->azTemp, pBe->nTemp*sizeof(char*) );
  }
  if( pBe->apTemp==0 ){
    *ppFile = 0;
    return SQLITE_NOMEM;
  }
  limit = 4;
  zFile = 0;
  do{
    randomName(&pBe->rc4, zBuf, "/_temp_file_");
    sqliteFree(zFile);
    zFile = 0;
    sqliteSetString(&zFile, pBe->zDir, zBuf, 0);
  }while( access(zFile,0)==0 && limit-- >= 0 );
  *ppFile = pBe->apTemp[i] = fopen(zFile, "w+");
  if( pBe->apTemp[i]==0 ){
    rc = SQLITE_ERROR;
    sqliteFree(zFile);
    pBe->azTemp[i] = 0;
  }else{
    pBe->azTemp[i] = zFile;
  }
  return rc;
}

/*
** Close a temporary file opened using sqliteGdbmOpenTempFile()
*/
static void sqliteGdbmCloseTempFile(Dbbe *pDbbe, FILE *f){
  int i;
  Dbbex *pBe = (Dbbex*)pDbbe;
  for(i=0; i<pBe->nTemp; i++){
    if( pBe->apTemp[i]==f ){
      unlink(pBe->azTemp[i]);
      sqliteFree(pBe->azTemp[i]);
      pBe->apTemp[i] = 0;
      pBe->azTemp[i] = 0;
      break;
    }
  }
  fclose(f);
}


/*
** This routine opens a new database.  For the GDBM driver
** implemented here, the database name is the name of the directory
** containing all the files of the database.
**
** If successful, a pointer to the Dbbe structure is returned.
** If there are errors, an appropriate error message is left
** in *pzErrMsg and NULL is returned.
*/
Dbbe *sqliteGdbmOpen(
  const char *zName,     /* The name of the database */
  int writeFlag,         /* True if we will be writing to the database */
  int createFlag,        /* True to create database if it doesn't exist */
  char **pzErrMsg        /* Write error messages (if any) here */
){
  Dbbex *pNew;
  struct stat statbuf;
  char *zMaster;

  if( !writeFlag ) createFlag = 0;
  if( stat(zName, &statbuf)!=0 ){
    if( createFlag ) mkdir(zName, 0750);
    if( stat(zName, &statbuf)!=0 ){
      sqliteSetString(pzErrMsg, createFlag ? 
         "can't find or create directory \"" : "can't find directory \"",
         zName, "\"", 0);
      return 0;
    }
  }
  if( !S_ISDIR(statbuf.st_mode) ){
    sqliteSetString(pzErrMsg, "not a directory: \"", zName, "\"", 0);
    return 0;
  }
  if( access(zName, writeFlag ? (X_OK|W_OK|R_OK) : (X_OK|R_OK)) ){
    sqliteSetString(pzErrMsg, "access permission denied", 0);
    return 0;
  }
  zMaster = 0;
  sqliteSetString(&zMaster, zName, "/" MASTER_NAME ".tbl", 0);
  if( stat(zMaster, &statbuf)==0
   && access(zMaster, writeFlag ? (W_OK|R_OK) : R_OK)!=0 ){
    sqliteSetString(pzErrMsg, "access permission denied for ", zMaster, 0);
    sqliteFree(zMaster);
    return 0;
  }
  sqliteFree(zMaster);
  pNew = sqliteMalloc(sizeof(Dbbex) + strlen(zName) + 1);
  if( pNew==0 ){
    sqliteSetString(pzErrMsg, "out of memory", 0);
    return 0;
  }
  pNew->dbbe.Close = sqliteGdbmClose;
  pNew->dbbe.OpenCursor = sqliteGdbmOpenCursor;
  pNew->dbbe.DropTable = sqliteGdbmDropTable;
  pNew->dbbe.ReorganizeTable = sqliteGdbmReorganizeTable;
  pNew->dbbe.CloseCursor = sqliteGdbmCloseCursor;
  pNew->dbbe.Fetch = sqliteGdbmFetch;
  pNew->dbbe.Test = sqliteGdbmTest;
  pNew->dbbe.CopyKey = sqliteGdbmCopyKey;
  pNew->dbbe.CopyData = sqliteGdbmCopyData;
  pNew->dbbe.ReadKey = sqliteGdbmReadKey;
  pNew->dbbe.ReadData = sqliteGdbmReadData;
  pNew->dbbe.KeyLength = sqliteGdbmKeyLength;
  pNew->dbbe.DataLength = sqliteGdbmDataLength;
  pNew->dbbe.NextKey = sqliteGdbmNextKey;
  pNew->dbbe.Rewind = sqliteGdbmRewind;
  pNew->dbbe.New = sqliteGdbmNew;
  pNew->dbbe.Put = sqliteGdbmPut;
  pNew->dbbe.Delete = sqliteGdbmDelete;
  pNew->dbbe.OpenTempFile = sqliteGdbmOpenTempFile;
  pNew->dbbe.CloseTempFile = sqliteGdbmCloseTempFile;
  pNew->zDir = (char*)&pNew[1];
  strcpy(pNew->zDir, zName);
  pNew->write = writeFlag;
  pNew->pOpen = 0;
  time(&statbuf.st_ctime);
  rc4init(&pNew->rc4, (char*)&statbuf, sizeof(statbuf));
  return &pNew->dbbe;
}

/*
** Copyright (c) 2001 D. Richard Hipp
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the GNU General Public
** License as published by the Free Software Foundation; either
** version 2 of the License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
** General Public License for more details.
** 
** You should have received a copy of the GNU General Public
** License along with this library; if not, write to the
** Free Software Foundation, Inc., 59 Temple Place - Suite 330,
** Boston, MA  02111-1307, USA.
**
** Author contact information:
**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*************************************************************************
** $Id: pg.c,v 1.1 2001/02/11 16:56:24 drh Exp $
*/
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include "sqliteInt.h"
#include "pg.h"

/*
** Uncomment the following for a debug trace
*/
#if 1
# define TRACE(X)  printf X; fflush(stdout);
#endif  

/*
** Hash table sizes
*/
#define J_HASH_SIZE  127  /* Size of the journal page hash table */
#define PG_HASH_SIZE 349  /* Size of the database page hash table */

/*
** Forward declaration of structure
*/
typedef struct Pghdr Pghdr;

/*
** All information about a single paging file is contained in an
** instance of the following structure.
*/
struct Pgr {
  int fdMain;                    /* The main database file */
  char *zMain;                   /* Name of the database file */
  int fdJournal;                 /* The journal file */
  char *zJournal;                /* Name of the journal file */
  int nMemPg;                    /* Number of memory-resident pages */
  int nJPg;                      /* Number of pages in the journal */
  int nDbPg;                     /* Number of pages in the database */
  int nRefPg;                    /* Number of pages currently in use */
  Pghdr *pLru, *pMru;            /* Least and most recently used mem-page */
  Pghdr *pJidx;                  /* List of journal index pages */
  Pghdr *pAll;                   /* All pages, except journal index pages */
  u32 aJHash[J_HASH_SIZE];       /* Journal page hash table */
  Pghdr *aPgHash[PG_HASH_SIZE];  /* Mem-page hash table */
};

/*
** Each memory-resident page of the paging file has a header which
** is an instance of the following structure.
*/
struct Pghdr {
  Pgr *p;            /* Pointer back to the Pgr structure */
  int nRef;          /* Number of references to this page */
  int isDirty;       /* TRUE if needs to be written to disk */
  u32 dbpgno;        /* Page number in the database file */
  u32 jpgno;         /* Page number in the journal file */
  Pghdr *pNx;        /* Next page on a list of them all */
  Pghdr *pLru;       /* Less recently used pages */
  Pghdr *pMru;       /* More recently used pages */
  Pghdr *pNxHash;    /* Next with same dbpgno hash */
  Pghdr *pPvHash;    /* Previous with the same dbpgno hash */
};

/*
** For a memory-resident page, the page data comes immediately after
** the page header.  The following macros can be used to change a 
** pointer to a page header into a pointer to the data, or vice
** versa.
*/
#define PG_TO_DATA(X)  ((void*)&(X)[1])
#define DATA_TO_PG(X)  (&((Pghdr*)(X))[-1])

/*
** The number of in-memory pages that we accumulate before trying
** to reuse older pages when new ones are requested.
*/
#define MX_MEM_PAGE  100

/*
** The number of journal data pages that come between consecutive 
** journal index pages.
*/
#define N_J_DATAPAGE  (SQLITE_PAGE_SIZE/(2*sizeof(u32)))

/*
** An index page in the journal consists of an array of N_J_DATAPAGE
** of the following structures.  There is one instance of the following
** structure for each of the N_J_DATAPAGE data pages that follow the
** index.
**
** Let the journal page number that a JidxEntry describes be J.  Then
** the JidxEntry.dbpgno field is the page of the database file that
** corresponds to the J page in the journal.  The JidxEntry.next_jpgno
** field hold the number of another journal page that contains
** a database file page with the same hash as JidxEntry.dbpgno.
**
** All information is written to the journal index in big-endian
** notation.
*/
typedef struct JidxEntry JidxEntry;
struct JidxEntry {
  char dbpgno[sizeof(u32)];        /* Database page number for this entry */
  char next_jpgno[sizeof(u32)];    /* Next entry with same hash on dbpgno */
};

/*
** Read a page from a file into memory.  Return SQLITE_OK if successful.
** The "pgno" parameter tells where in the file to read the page.
** The first page is 1.  Files do not contain a page 0 since a page
** number of 0 is used to indicate "no such page".
*/
static int sqlitePgRead(int fd, char *zBuf, u32 pgno){
  int got = 0;
  int amt;

  assert( pgno>0 );
  assert( fd>=0 );
  lseek(fd, SEEK_SET, (pgno-1)*SQLITE_PAGE_SIZE);
  while( got<SQLITE_PAGE_SIZE ){
    amt = read(fd, &zBuf[got], SQLITE_PAGE_SIZE - got);
    if( amt<=0 ){
      memset(&zBuf[got], 0, SQLITE_PAGE_SIZE - got);
      return amt==0 ? SQLITE_OK : SQLITE_IOERR;
    }
    got += amt;
  }
  return SQLITE_OK;
}

/*
** Read a page from a file into memory.  Return SQLITE_OK if successful.
** The "pgno" parameter tells where in the file to write the page.
** The first page is 1.  Files do not contain a page 0 since a page
** number of 0 is used to indicate "no such page".
*/
static int sqlitePgWrite(int fd, char *zBuf, u32 pgno){
  int done = 0;
  int amt;

  assert( pgno>0 );
  assert( fd>=0 );
  lseek(fd, SEEK_SET, (pgno-1)*SQLITE_PAGE_SIZE);
  while( done<SQLITE_PAGE_SIZE ){
    amt = write(fd, &zBuf[done], SQLITE_PAGE_SIZE - done);
    if( amt<=0 ) return SQLITE_IOERR;
    done += amt;
  }
  return SQLITE_OK;
}

/*
** Turn four bytes into an integer.  The first byte is always the
** most significant 8 bits.
*/
static u32 sqlitePgGetInt(const char *p){
  return ((p[0]&0xff)<<24) | ((p[1]&0xff)<<16) | ((p[2]&0xff)<<8) | (p[3]&0xff);
}

/*
** Turn an integer into 4 bytes.  The first byte is always the
** most significant 8 bits.
*/
static void sqlitePgPutInt(u32 v, char *p){
  p[3] = v & 0xff;
  v >>= 8;
  p[2] = v & 0xff;
  v >>= 8;
  p[1] = v & 0xff;
  v >>= 8;
  p[0] = v & 0xff;
}

/*
** Check the hash table for an in-memory page.  Return a pointer to
** the page header if found.  Return NULL if the page is not in memory.
*/
static Pghdr *sqlitePgFind(Pgr *p, u32 pgno){
  int h;
  Pghdr *pPg;

  if( pgno==0 ) return 0;
  h = pgno % PG_HASH_SIZE;
  for(pPg = p->aPgHash[h]; pPg; pPg=pPg->pNxHash){
    if( pPg->dbpgno==pgno ) return pPg;
  }
  TRACE(("PG: data page %u is %#x\n", pgno, (u32)pPg));
  return 0;
}

/*
** Locate and return an index page from the journal.
**
** The first page of a journal is the primary index.  Additional
** index pages are called secondary indices.  Index pages appear
** in the journal as often as needed.  (If SQLITE_PAGE_SIZE==1024,
** then there are 1024/sizeof(int)*2 = 128 database between each
** pair of index pages.)  Journal index pages are not hashed and
** do no appear on the Pgr.pAll list.  Index pages are on the
** Pgr.pJidx list only.  Index pages have Pghdr.dbpgno==0.
**
** If the requested index page is not already in memory, then a
** new memory page is created to hold the index.
**
** This routine will return a NULL pointer if we run out of memory.
*/
static Pghdr *sqlitePgFindJidx(Pgr *p, u32 pgno){
  Pghdr *pPg;

  assert( pgno % (N_J_DATAPAGE+1) == 1 );
  for(pPg=p->pJidx; pPg; pPg=pPg->pNx){
    if( pPg->jpgno==pgno ){
      TRACE(("PG: found j-index %u at %#x\n", pgno, (u32)pPg));
      return pPg;
    }
  }
  pPg = sqliteMalloc( sizeof(Pghdr)+SQLITE_PAGE_SIZE );
  if( pPg==0 ) return 0;
  pPg->jpgno = pgno;
  pPg->pNx = p->pJidx;
  p->pJidx = pPg;
  sqlitePgRead(p->fdJournal, PG_TO_DATA(pPg), pgno);
  TRACE(("PG: create j-index %u at %#x\n", pgno, (u32)pPg));
  return pPg;
}

/*
** Look in the journal to see if the given database page is stored
** in the journal.  If it is, return its journal page number.  If
** not, return 0.
*/
static u32 sqlitePgJournalPageNumber(Pgr *p, u32 dbpgno){
  u32 jpgno;
  
  if( dbpgno==0 ) return 0;
  jpgno = p->aJHash[dbpgno % J_HASH_SIZE];
  while( jpgno!=0 ){
    int idx_num;     /* Which journal index describes page jpgno */
    int ipgno;       /* Page number for the journal index */
    int idx_slot;    /* Which entry in index idx_num describes jpgno */
    Pghdr *pIdxPg;   /* The index page for jpgno */
    JidxEntry *aIdx; /* The data for the index page */

    idx_num = (jpgno - 1)/(N_J_DATAPAGE + 1);
    idx_slot = (jpgno - 1) % (N_J_DATAPAGE + 1) - 2;
    ipgno = idx_num * (N_J_DATAPAGE + 1) + 1;
    if( ipgno>p->nJPg ){
      jpgno = 0;
      break;
    }
    pIdxPg = sqlitePgFindJidx(p, ipgno);
    assert( pIdxPg!=0 );
    aIdx = PG_TO_DATA(pIdxPg);
    if( dbpgno==sqlitePgGetInt(aIdx[idx_slot].dbpgno) ){
      break;
    }
    jpgno = sqlitePgGetInt(aIdx[idx_slot].next_jpgno);
  }
  return jpgno;
}

/*
** Make a page not dirty by writing it to the journal.
*/
static int sqlitePgMakeClean(Pghdr *pPg){
  Pgr *p = pPg->p;
  int rc;

  assert( pPg->isDirty );
  assert( p->fdJournal>=0 );
  if( pPg->jpgno==0 ){
    int jpgno;       /* A newly allocate page in the journal */
    int idx_num;     /* Which journal index describes page jpgno */
    int idx_slot;    /* Which entry in index idx_num describes jpgno */
    Pghdr *pIdxPg;   /* The index page for jpgno */
    JidxEntry *aIdx; /* The data for the index page */
    int h;           /* The hash value for pPg->dbpgno */

    jpgno = p->nJPg + 1;
    if( jpgno % (N_J_DATAPAGE + 1) == 1 ){
      jpgno++;
    }
    idx_num = (jpgno - 1)/(N_J_DATAPAGE + 1);
    idx_slot = (jpgno - 1) % (N_J_DATAPAGE + 1) - 2;
    pIdxPg = sqlitePgFindJidx(p, idx_num * (N_J_DATAPAGE + 1) + 1);
    assert( pIdxPg!=0 );
    aIdx = PG_TO_DATA(pIdxPg);
    sqlitePgPutInt(pPg->dbpgno, aIdx[idx_slot].dbpgno);
    h = pPg->dbpgno % J_HASH_SIZE;
    sqlitePgPutInt(p->aJHash[h], aIdx[idx_slot].next_jpgno);
    p->aJHash[h] = jpgno;
    p->nJPg = jpgno;
    pPg->jpgno = jpgno;
    TRACE(("PG: assign d-page %u to j-page %u\n", jpgno, pPg->dbpgno));
  }
  rc = sqlitePgWrite(p->fdJournal, PG_TO_DATA(pPg), pPg->jpgno);
  if( rc==SQLITE_OK ){
    pPg->isDirty = 0;
  }
  return rc;
}

/*
** Find the number of pages in the given file by measuring the size
** of the file.  Return 0 if there is any problem.
*/
static int sqlitePgPageCount(int fd){
  struct stat statbuf;
  if( fstat(fd, &statbuf)!=0 ) return 0;
  return statbuf.st_size/SQLITE_PAGE_SIZE;
}

/*
** This routine reads the journal and transfers pages from the
** journal to the database.
*/
static int sqlitePgJournalPlayback(Pgr *p){
  Pghdr *pPg;
  JidxEntry *aIdx;
  int nJpg;
  int jpgno = 1;
  int i;
  int dbpgno;
  int rc;
  char idx[SQLITE_PAGE_SIZE];
  char pgbuf[SQLITE_PAGE_SIZE];
  
  assert( p->fdJournal>=0 );
  nJpg = sqlitePgPageCount(p->fdJournal);
  while( jpgno<=nJpg ){
    if( !sqlitePgRead(p->fdJournal, idx, jpgno++) ) break;
    aIdx = (JidxEntry*)idx;
    for(i=0; i<N_J_DATAPAGE; i++){
      dbpgno = sqlitePgGetInt(&idx[i]);
      if( dbpgno==0 ){
        jpgno = nJpg+1;
        break;
      }
      pPg = sqlitePgFind(p, dbpgno);
      if( pPg ){
        rc = sqlitePgWrite(p->fdMain, PG_TO_DATA(pPg), dbpgno);
        TRACE(("PG: commit j-page %u to d-page %u from memory\n",jpgno,dbpgno));
      }else{
        rc = sqlitePgRead(p->fdJournal, pgbuf, jpgno);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        rc = sqlitePgWrite(p->fdMain, pgbuf, dbpgno);
        TRACE(("PG: commit j-page %u to d-page %u from disk\n",jpgno,dbpgno));
      }
      jpgno++;
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
  }
  TRACE(("PG: commit complete. deleting the journal.\n"));
  fsync(p->fdMain);
  close(p->fdJournal);
  p->fdJournal = -1;
  unlink(p->zJournal);
  for(pPg=p->pAll; pPg; pPg=pPg->pNx){
    pPg->isDirty = 0;
    pPg->jpgno = 0;
  }
  while( (pPg = p->pJidx)!=0 ){
    p->pAll = pPg->pNx;
    sqliteFree(pPg);
  }
  return SQLITE_OK;
}

/*
** Remove the given page from the LRU list.
*/
static void sqlitePgUnlinkLru(Pghdr *pPg){
  Pgr *p = pPg->p;
  if( pPg->pLru ){
    pPg->pLru->pMru = pPg->pLru;
  }
  if( pPg->pMru ){
    pPg->pMru->pLru = pPg->pMru;
  }
  if( p->pLru==pPg ){
    p->pLru = pPg->pLru;
  }
  if( p->pMru==pPg ){
    p->pMru = pPg->pMru;
  }
  pPg->pLru = pPg->pMru = 0;
}

/*
** Open the database file and make *ppPgr pointer to a structure describing it.
** Return SQLITE_OK on success or an error code if there is a failure.
**
** If there was an unfinished commit, complete it before returnning.
*/
int sqlitePgOpen(const char *zFilename, Pgr **ppPgr){
  Pgr *p;
  int n;

  n = strlen(zFilename);
  p = sqliteMalloc( sizeof(*p) + n*2 + 4 );
  if( p==0 ){
    *ppPgr = 0;
    return SQLITE_NOMEM;
  }
  p->zMain = (char*)&p[1];
  strcpy(p->zMain, zFilename);
  p->zJournal = &p->zMain[n+1];
  strcpy(p->zJournal, p->zMain);
  p->zJournal[n] = '~';
  p->zJournal[n+1] = 0;
  p->fdJournal = -1;
  p->fdMain = open(p->zMain, O_CREAT|O_RDWR, 0600);
  if( p->fdMain<0 ){
    *ppPgr = 0;
    sqliteFree(p);
    return SQLITE_PERM;
  }
  p->nDbPg = sqlitePgPageCount(p->fdMain);
  if( access(p->zJournal, R_OK)==0 ){
    sqlitePgJournalPlayback(p);
  }
  *ppPgr = p;
  return SQLITE_OK;
}

/*
** Close the database file.  Any outstanding transactions are abandoned.
*/
int sqlitePgClose(Pgr *p){
  Pghdr *pPg;

  if( p->fdMain ) close(p->fdMain);
  if( p->fdJournal ) close(p->fdJournal);
  unlink(p->zJournal);
  while( (pPg = p->pAll)!=0 ){
    p->pAll = pPg->pNx;
    sqliteFree(pPg);
  }
  while( (pPg = p->pJidx)!=0 ){
    p->pAll = pPg->pNx;
    sqliteFree(pPg);
  }
  sqliteFree(p);
  return SQLITE_OK;
}

/*
** Begin a new transaction.  Return SQLITE_OK on success or an error
** code if something goes wrong.
*/
int sqlitePgBeginTransaction(Pgr *p){
  assert( p->fdJournal<0 );
  if( p->nRefPg>0 ){
     /* release the read lock */
  }
  /* write lock the database */
  p->fdJournal = open(p->zJournal, O_CREAT|O_EXCL|O_RDWR, 0600);
  if( p->fdJournal<0 ){
    return SQLITE_PERM;
  }
  p->nJPg = 0;
  TRACE(("PG: begin transaction\n"));
  return SQLITE_OK;
}

/*
** Commit the current transaction.  Return SQLITE_OK or an error code.
*/
int sqlitePgCommit(Pgr *p){
  Pghdr *pPrimaryIdx = 0;
  Pghdr *pPg;
  int rc;

  for(pPg=p->pAll; pPg; pPg=pPg->pNx){
    if( pPg->isDirty ){
      rc = sqlitePgMakeClean(pPg);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
  }
  for(pPg=p->pJidx; pPg; pPg=pPg->pNx){
    if( pPg->jpgno==1 ){
      pPrimaryIdx = pPg;
    }else{
      TRACE(("PG: writing j-index %u\n", pPg->jpgno));
      rc = sqlitePgMakeClean(pPg);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
  }
  assert( pPrimaryIdx!=0 );
  fsync(p->fdJournal);
  TRACE(("PG: writing j-index %u\n", pPrimaryIdx->jpgno));
  rc = sqlitePgMakeClean(pPrimaryIdx);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  fsync(p->fdJournal);
  rc = sqlitePgJournalPlayback(p);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  /* remove write lock from database */
  if( p->nRefPg>0 ){
    /* acquire read lock on database */
  }
  return SQLITE_OK;
}

/*
** Abandon the current transaction.
*/
int sqlitePgRollback(Pgr *p){
  Pghdr *pPg;

  TRACE(("PG: begin rollback\n"));
  for(pPg=p->pAll; pPg; pPg=pPg->pNx){
    if( pPg->isDirty || pPg->jpgno!=0 ){
      pPg->isDirty = 0;
      pPg->jpgno = 0;
      if( pPg->nRef>0 ){
        TRACE(("PG: reloading d-page %u\n", pPg->dbpgno));
        sqlitePgRead(p->fdMain, PG_TO_DATA(pPg), pPg->dbpgno);
      }else{
        sqlitePgUnlinkLru(pPg);
      }
    }
  }
  close(p->fdJournal);
  p->fdJournal = -1;
  unlink(p->zJournal);
  while( (pPg = p->pJidx)!=0 ){
    p->pAll = pPg->pNx;
    sqliteFree(pPg);
  }
  p->nDbPg = sqlitePgPageCount(p->fdMain);
  /* remove write lock from database */
  if( p->nRefPg>0 ){
    /* acquire read lock on database */
  }
  return SQLITE_OK;
}

/*
** Get a page from the database.  Return a pointer to the data for that
** page.
**
** A NULL pointer will be returned if we run out of memory.
*/
int sqlitePgGet(Pgr *p, u32 pgno, void **ppData){
  Pghdr *pPg;
  int h;

  pPg = sqlitePgFind(p, pgno);
  if( pPg ){
    pPg->nRef++;
    if( pPg->nRef==1 ){
      sqlitePgUnlinkLru(pPg);
      TRACE(("PG: d-page %u pulled from cache\n", pgno));
    }
    p->nRefPg++;
    if( p->nRefPg==1 ){
      /* Acquire a read lock */
    }
    *ppData = PG_TO_DATA(pPg);
    return SQLITE_OK;
  }
  if( p->nMemPg<MX_MEM_PAGE || p->pLru==0 ){
    pPg = sqliteMalloc( sizeof(Pghdr) + SQLITE_PAGE_SIZE );
    if( pPg==0 ) return SQLITE_NOMEM;
    p->nMemPg++;
    pPg->pNx = p->pAll;
    p->pAll = pPg;
    pPg->p = p;
    TRACE(("PG: new page %d created.\n", p->nMemPg));
  }else{
    int rc;
    pPg = p->pLru;
    if( pPg->isDirty ){
      rc = sqlitePgMakeClean(pPg);
      if( rc!=SQLITE_OK ) return rc;
    }
    sqlitePgUnlinkLru(pPg);
    h = pPg->dbpgno % PG_HASH_SIZE;
    if( pPg->pPvHash ){
      pPg->pPvHash->pNxHash = pPg->pNxHash;
    }else{
      assert( p->aPgHash[h]==pPg );
      p->aPgHash[h] = pPg->pNxHash;
    }
    if( pPg->pNxHash ){
      pPg->pNxHash->pPvHash = pPg->pPvHash;
    }
    TRACE(("PG: recycling d-page %u to d-page %u\n", pPg->dbpgno, pgno));
  }
  pPg->dbpgno = pgno;
  if( pgno>p->nDbPg ){
    p->nDbPg = pgno;
  }
  h = pgno % PG_HASH_SIZE;
  pPg->pPvHash = 0;
  pPg->pNxHash = p->aPgHash[h];
  if( pPg->pNxHash ){
    pPg->pNxHash->pPvHash = pPg;
  }
  p->aPgHash[h] = pPg;
  pPg->jpgno = sqlitePgJournalPageNumber(p, pgno);
  if( pPg->jpgno!=0 ){
    TRACE(("PG: reading d-page %u content from j-page %u\n", pgno, pPg->jpgno));
    sqlitePgRead(p->fdJournal, PG_TO_DATA(pPg), pPg->jpgno);
  }else if( pPg->dbpgno!=0 ){
    TRACE(("PG: reading d-page %u from database\n", pgno));
    sqlitePgRead(p->fdMain, PG_TO_DATA(pPg), pPg->dbpgno);
  }else{
    TRACE(("PG: reading zero page\n");
    memset(PG_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
  }
  pPg->isDirty = 0;
  pPg->nRef = 1;
  p->nRefPg++;
  if( p->nRefPg==1 ){
    /* Acquire a read lock */
  }
  *ppData = PG_TO_DATA(pPg);
  return SQLITE_OK;
}

/*
** Release a reference to a database data page.
*/
int sqlitePgUnref(void *pData){
  Pghdr *pPg = DATA_TO_PG(pData);
  pPg->nRef--;
  assert( pPg->nRef>=0 );
  if( pPg->nRef==0 ){
    Pgr *p = pPg->p;
    pPg->pMru = 0;
    pPg->pLru = p->pLru;
    p->pLru = pPg;
    TRACE(("PG: d-page %u is unused\n", pPg->dbpgno));
    p->nRefPg--;
    if( p->nRefPg==0 ){
      /* Release the read lock */
    }
  }
  return SQLITE_OK;
}

/*
** The database page in the argument has been modified.  Write it back
** to the database file on the next commit.
*/
int sqlitePgTouch(void *pD){
  Pghdr *pPg = DATA_TO_PG(pD);
  assert( pPg->p->fdJournal>=0 );
  if( pPg->isDirty==0 ){
    pPg->isDirty = 1;
    TRACE(("PG: d-page %u is dirty\n", pPg->dbpgno));
  }
  return SQLITE_OK;
}

/*
** Return the number of the first unused page at the end of the
** database file.
*/
int sqlitePgCount(Pgr *p, u32 *pPgno){
  *pPgno = p->nDbPg;
  return SQLITE_OK;
}

/*
** Return the page number associated with the given page.
*/
u32 sqlitePgNum(void *pD){
  Pghdr *pPg = DATA_TO_PG(pD);
  return pPg->dbpgno;
}

/*
** Copyright (c) 2001 D. Richard Hipp
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the GNU General Public
** License as published by the Free Software Foundation; either
** version 2 of the License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
** General Public License for more details.
** 
** You should have received a copy of the GNU General Public
** License along with this library; if not, write to the
** Free Software Foundation, Inc., 59 Temple Place - Suite 330,
** Boston, MA  02111-1307, USA.
**
** Author contact information:
**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*************************************************************************
** $Id: pg.h,v 1.1 2001/02/11 16:56:24 drh Exp $
*/

typedef struct Pgr Pgr;
#define SQLITE_PAGE_SIZE 1024


int sqlitePgOpen(const char *filename, Pgr **pp);
int sqlitePgClose(Pgr*);
int sqlitePgBeginTransaction(Pgr*);
int sqlitePgCommit(Pgr*);
int sqlitePgRollback(Pgr*);
int sqlitePgGet(Pgr*, u32 pgno, void **);
int sqlitePgUnref(void*);
int sqlitePgTouch(void*);
int sqlitePgCount(Pgr*, u32*);
u32 sqlitePgNum(void*);

set sizes {1024 2048 4096 8192 16384 32768}
set fmt { %-8s}

puts -nonewline "page size: "
foreach s $sizes {
  puts -nonewline [format $fmt $s]
}
puts ""

puts -nonewline "on leaf:   "
foreach s $sizes {
  set x [expr {$s - 18*4}]
  set p($s) $x
  puts -nonewline [format $fmt $x]
}
puts ""

puts -nonewline "direct:    "
foreach s $sizes {
  set x [expr {$p($s) + 10*$s}]
  set p($s) $x
  puts -nonewline [format $fmt $x]
}
puts ""

puts -nonewline "indirect:  "
foreach s $sizes {
  set x [expr {$p($s) + ($s/4.0)*$s}]
  set p($s) $x
  puts -nonewline [format $fmt $x]
}
puts ""

puts -nonewline "dbl indir: "
foreach s $sizes {
  set x [expr {$p($s) + ($s/4.0)*($s/4)*$s}]
  set p($s) $x
  puts -nonewline [format $fmt $x]
}
puts ""