}

int test_lsm_small_open(
  const char *zFile, 
  int bClear, 
  TestDb **ppDb
){
  const char *zCfg = "page_size=256 block_size=64 mmap=1024";
  return testLsmOpen(zCfg, zFile, bClear, ppDb);
}

int test_lsm_lomem_open(
  const char *zFilename, 
  int bClear, 
  TestDb **ppDb

    struct Config {
      const char *zParam;
      int eParam;
    } aConfig[] = {
      { "lsm_mmap", LSM_CONFIG_MMAP },
      { "lsm_page_size", LSM_CONFIG_PAGE_SIZE },
      { "lsm_block_size", LSM_CONFIG_BLOCK_SIZE },
      { "lsm_multiple_processes", LSM_CONFIG_MULTIPLE_PROCESSES },
      { "lsm_automerge", LSM_CONFIG_AUTOMERGE }
    };

    memset(pNew, 0, sizeof(KVLsm));
    pNew->base.pStoreVfunc = &kvlsmMethods;
    pNew->base.pEnv = pEnv;
    rc = lsm_new(0, &pNew->pDb);
    if( rc==SQLITE4_OK ){
      int i;



      for(i=0; i<ArraySize(aConfig); i++){
        const char *zVal = sqlite4_uri_parameter(zName, aConfig[i].zParam);
        if( zVal ){
          int nVal = sqlite4Atoi(zVal);
          lsm_config(pNew->pDb, aConfig[i].eParam, &nVal);
        }
      }

**   This means that this option may cause the connection to perform a 
**   checkpoint even if the current connection has itself written very little
**   data into the database file.
**
**   The default value is 2048 (checkpoint every 2MB).
**
** LSM_CONFIG_MMAP:
**   A read/write integer parameter. If this value is set to 0, then the 
**   database file is accessed using ordinary read/write IO functions. Or,
**   if it is set to 1, then the database file is memory mapped and accessed
**   that way. If this parameter is set to any value N greater than 1, then
**   up to the first N KB of the file are memory mapped, and any remainder
**   accessed using read/write IO.
**
**   The default value is 1 on 64-bit platforms and 32768 on 32-bit platforms.
**   
**
** LSM_CONFIG_USE_LOG:
**   A read/write boolean parameter. True (the default) to use the log
**   file normally. False otherwise.
**
** LSM_CONFIG_AUTOMERGE:
**   A read/write integer parameter. The minimum number of segments to

#define LSM_DFLT_BLOCK_SIZE         (1 * 1024 * 1024)
#define LSM_DFLT_AUTOFLUSH          (1 * 1024 * 1024)
#define LSM_DFLT_AUTOCHECKPOINT     (i64)(2 * 1024 * 1024)
#define LSM_DFLT_AUTOWORK           1
#define LSM_DFLT_LOG_SIZE           (128*1024)
#define LSM_DFLT_AUTOMERGE          4
#define LSM_DFLT_SAFETY             LSM_SAFETY_NORMAL
#define LSM_DFLT_MMAP               (LSM_IS_64_BIT ? 1 : 32768)
#define LSM_DFLT_MULTIPLE_PROCESSES 1
#define LSM_DFLT_USE_LOG            1

/* Initial values for log file checksums. These are only used if the 
** database file does not contain a valid checkpoint.  */
#define LSM_CKSUM0_INIT 42
#define LSM_CKSUM1_INIT 42

  int bAutowork;                  /* Configured by LSM_CONFIG_AUTOWORK */
  int nTreeLimit;                 /* Configured by LSM_CONFIG_AUTOFLUSH */
  int nMerge;                     /* Configured by LSM_CONFIG_AUTOMERGE */
  int bUseLog;                    /* Configured by LSM_CONFIG_USE_LOG */
  int nDfltPgsz;                  /* Configured by LSM_CONFIG_PAGE_SIZE */
  int nDfltBlksz;                 /* Configured by LSM_CONFIG_BLOCK_SIZE */
  int nMaxFreelist;               /* Configured by LSM_CONFIG_MAX_FREELIST */
  int iMmap;                      /* Configured by LSM_CONFIG_MMAP */
  i64 nAutockpt;                  /* Configured by LSM_CONFIG_AUTOCHECKPOINT */
  int bMultiProc;                 /* Configured by L_C_MULTIPLE_PROCESSES */
  int bReadonly;                  /* Configured by LSM_CONFIG_READONLY */
  lsm_compress compress;          /* Compression callbacks */
  lsm_compress_factory factory;   /* Compression callback factory */

  /* Sub-system handles */

#include <sys/stat.h>
#include <fcntl.h>

/*
** File-system object. Each database connection allocates a single instance
** of the following structure. It is used for all access to the database and
** log files.
**
** The database file may be accessed via two methods - using mmap() or using
** read() and write() calls. In the general case both methods are used - a
** prefix of the file is mapped into memory and the remainder accessed using
** read() and write(). This is helpful when accessing very large files (or
** files that may grow very large during the lifetime of a database
** connection) on systems with 32-bit address spaces. However, it also requires
** that this object manage two distinct types of Page objects simultaneously -
** those that carry pointers to the mapped file and those that carry arrays
** populated by read() calls.
**
** pFree:
**   The head of a singly-linked list that containing currently unused Page 
**   structures suitable for use as mmap-page handles. Connected by the
**   Page.pFreeNext pointers.

**
** pMapped:
**   The head of a singly-linked list that contains all pages that currently
**   carry pointers to the mapped region. This is used if the region is

**   every remapped - the pointers carried by existing pages can be adjusted
**   to account for the remapping. Connected by the Page.pMappedNext pointers.
**
** pWaiting:
**   When the upper layer wishes to append a new b-tree page to a segment,
**   it allocates a Page object that carries a malloc'd block of memory -
**   regardless of the mmap-related configuration. The page is not assigned
**   a page number at first. When the upper layer has finished constructing
**   the page contents, it calls lsmFsPagePersist() to assign a page number
**   to it. At this point it is likely that N pages have been written to the
**   segment, the (N+1)th page is still outstanding and the b-tree page is
**   assigned page number (N+2). To avoid writing page (N+2) before page 
**   (N+1), the recently completed b-tree page is held in the singly linked
**   list headed by pWaiting until page (N+1) has been written. 
**
**   Function lsmFsFlushWaiting() is responsible for eventually writing 
**   waiting pages to disk.
**
**
** apHash/nHash:
**   Hash table used to store all Page objects that carry malloc'd arrays,
**   except those b-tree pages that have not yet been assigned page numbers.
**   Once they have been assigned page numbers - they are added to this
**   hash table.
**
**   Hash table overflow chains are connected using the Page.pHashNext
**   pointers.
**
** pLruFirst, pLruLast:
**   The first and last entries in a doubly-linked list of pages. This
**   list contains all pages with malloc'd data that are present in the
**   hash table and have a ref-count of zero.
*/
struct FileSystem {
  lsm_db *pDb;                    /* Database handle that owns this object */
  lsm_env *pEnv;                  /* Environment pointer */
  char *zDb;                      /* Database file name */
  char *zLog;                     /* Database file name */
  int nMetasize;                  /* Size of meta pages in bytes */

  int szSector;                   /* Database file sector size */

  /* If this is a compressed database, a pointer to the compression methods.
  ** For an uncompressed database, a NULL pointer.  */
  lsm_compress *pCompress;
  u8 *aIBuffer;                   /* Buffer to compress to */
  u8 *aOBuffer;                   /* Buffer to uncompress from */
  int nBuffer;                    /* Allocated size of above buffers in bytes */

  /* mmap() page related things */
  i64 nMapLimit;                  /* Maximum bytes of file to map */
  void *pMap;                     /* Current mapping of database file */
  i64 nMap;                       /* Bytes mapped at pMap */
  Page *pFree;                    /* Unused Page structures */
  Page *pMapped;                  /* List of Page structs that point to pMap */






  /* Page cache parameters for non-mmap() pages */

  int nCacheMax;                  /* Configured cache size (in pages) */
  int nCacheAlloc;                /* Current cache size (in pages) */
  Page *pLruFirst;                /* Head of the LRU list */
  Page *pLruLast;                 /* Tail of the LRU list */
  int nHash;                      /* Number of hash slots in hash table */
  Page **apHash;                  /* nHash Hash slots */
  Page *pWaiting;                 /* b-tree pages waiting to be written */

  /* Statistics */
  int nOut;                       /* Number of outstanding pages */
  int nWrite;                     /* Total number of pages written */
  int nRead;                      /* Total number of pages read */
};

/*
** Database page handle.
**
** pSeg:
**   When lsmFsSortedAppend() is called on a compressed database, the new

  FileSystem *pFS;                /* File system that owns this page */

  /* Only used in compressed database mode: */
  int nCompress;                  /* Compressed size (or 0 for uncomp. db) */
  int nCompressPrev;              /* Compressed size of prev page */
  Segment *pSeg;                  /* Segment this page will be written to */

  /* Pointers for singly linked lists */
  Page *pWaitingNext;             /* Next page in FileSystem.pWaiting list */
  Page *pFreeNext;                /* Next page in FileSystem.pFree list */
  Page *pMappedNext;              /* Next page in FileSystem.pMapped list */
};

/*
** Meta-data page handle. There are two meta-data pages at the start of
** the database file, each FileSystem.nMetasize bytes in size.
*/
struct MetaPage {

static int IOERR_WRAPPER(int rc){
  if( rc!=LSM_OK ) lsmIoerrBkpt();
  return rc;
}
#else
# define IOERR_WRAPPER(rc) (rc)
#endif

#ifdef NDEBUG
# define assert_lists_are_ok(x)
#else
static Page *fsPageFindInHash(FileSystem *pFS, Pgno iPg, int *piHash);

static void assert_lists_are_ok(FileSystem *pFS){
#if 0
  Page *p;

  assert( pFS->nMapLimit>=0 );

  /* Check that all pages in the LRU list have nRef==0, pointers to buffers
  ** in heap memory, and corresponding entries in the hash table.  */
  for(p=pFS->pLruFirst; p; p=p->pLruNext){
    assert( p==pFS->pLruFirst || p->pLruPrev!=0 );
    assert( p==pFS->pLruLast || p->pLruNext!=0 );
    assert( p->pLruPrev==0 || p->pLruPrev->pLruNext==p );
    assert( p->pLruNext==0 || p->pLruNext->pLruPrev==p );
    assert( p->nRef==0 );
    assert( p->flags & PAGE_FREE );
    assert( p==fsPageFindInHash(pFS, p->iPg, 0) );
  }
#endif
}
#endif

/*
** Wrappers around the VFS methods of the lsm_env object:
**
**     lsmEnvOpen()
**     lsmEnvRead()
**     lsmEnvWrite()

  zDel = lsmMallocPrintf(pFS->pEnv, "%s-log", pFS->zDb);
  if( zDel ){
    lsmEnvUnlink(pFS->pEnv, zDel);
    lsmFree(pFS->pEnv, zDel);
  }
  return LSM_OK;
}

/*
** Return true if page iReal of the database should be accessed using mmap.
** False otherwise.
*/
static int fsMmapPage(FileSystem *pFS, Pgno iReal){
  return ((i64)iReal*pFS->nPagesize <= pFS->nMapLimit);
}

/*
** Given that there are currently nHash slots in the hash table, return 
** the hash key for file iFile, page iPg.
*/
static int fsHashKey(int nHash, int iPg){
  return (iPg % nHash);

  FileSystem *pFS = db->pFS;
  if( pFS ){
    lsm_env *pEnv = pFS->pEnv;
    Page *pPg;

    assert( pFS->nOut==0 );
    assert( pFS->pWaiting==0 );
    assert( pFS->pMapped==0 );

    /* Reset any compression/decompression buffers already allocated */
    lsmFree(pEnv, pFS->aIBuffer);
    lsmFree(pEnv, pFS->aOBuffer);
    pFS->nBuffer = 0;

    /* Unmap the file, if it is currently mapped */
    if( pFS->pMap ){
      lsmEnvRemap(pEnv, pFS->fdDb, -1, &pFS->pMap, &pFS->nMap);
      pFS->nMapLimit = 0;
    }

    /* Free all allocated page structures */
    pPg = pFS->pLruFirst;
    while( pPg ){
      Page *pNext = pPg->pLruNext;
      assert( pPg->flags & PAGE_FREE );
      lsmFree(pEnv, pPg->aData);
      lsmFree(pEnv, pPg);
      pPg = pNext;
    }

    pPg = pFS->pFree;
    while( pPg ){
      Page *pNext = pPg->pFreeNext;
      lsmFree(pEnv, pPg);
      pPg = pNext;
    }

    /* Zero pointers that point to deleted page objects */
    pFS->nCacheAlloc = 0;
    pFS->pLruFirst = 0;
    pFS->pLruLast = 0;
    pFS->pFree = 0;
    if( pFS->apHash ){
      memset(pFS->apHash, 0, pFS->nHash*sizeof(pFS->apHash[0]));
    }

    /* Configure the FileSystem object */
    if( db->compress.xCompress ){
      pFS->pCompress = &db->compress;
      pFS->nMapLimit = 0;
    }else{
      pFS->pCompress = 0;
      if( db->iMmap==1 ){
        /* Unlimited */
        pFS->nMapLimit = (i64)1 << 60;
      }else{
        pFS->nMapLimit = (i64)db->iMmap * 1024;
      }
    }
  }

  return LSM_OK;
}

/*

static void fsPageRemoveFromHash(FileSystem *pFS, Page *pPg){
  int iHash;
  Page **pp;

  iHash = fsHashKey(pFS->nHash, pPg->iPg);
  for(pp=&pFS->apHash[iHash]; *pp!=pPg; pp=&(*pp)->pHashNext);
  *pp = pPg->pHashNext;
  pPg->pHashNext = 0;
}

static void fsPageBufferFree(Page *pPg){
  pPg->pFS->nCacheAlloc--;
  lsmFree(pPg->pFS->pEnv, pPg->aData);
  lsmFree(pPg->pFS->pEnv, pPg);
}


/*
** Purge the cache of all non-mmap pages with nRef==0.
*/
void lsmFsPurgeCache(FileSystem *pFS){

  Page *pPg;

  pPg = pFS->pLruFirst;
  while( pPg ){
    Page *pNext = pPg->pLruNext;
    assert( pPg->flags & PAGE_FREE );
    fsPageRemoveFromHash(pFS, pPg);



    fsPageBufferFree(pPg);
    pPg = pNext;

  }
  pFS->pLruFirst = 0;
  pFS->pLruLast = 0;

  assert( pFS->nCacheAlloc<=pFS->nOut && pFS->nCacheAlloc>=0 );

}

/*
** Search the hash-table for page iPg. If an entry is round, return a pointer
** to it. Otherwise, return NULL.
**
** Either way, if argument piHash is not NULL set *piHash to the hash slot
** number that page iPg would be stored in before returning.
*/
static Page *fsPageFindInHash(FileSystem *pFS, Pgno iPg, int *piHash){
  Page *p;                        /* Return value */
  int iHash = fsHashKey(pFS->nHash, iPg);

  if( piHash ) *piHash = iHash;
  for(p=pFS->apHash[iHash]; p; p=p->pHashNext){
    if( p->iPg==iPg) break;
  }
  return p;
}

/*
** Allocate and return a non-mmap Page object. If there are already 
** nCacheMax such Page objects outstanding, try to recycle an existing 
** Page instead.
*/
static int fsPageBuffer(
  FileSystem *pFS, 
  Page **ppOut
){
  int rc = LSM_OK;
  Page *pPage = 0;
  if( pFS->pLruFirst==0 || pFS->nCacheAlloc<pFS->nCacheMax ){
    pPage = lsmMallocZero(pFS->pEnv, sizeof(Page));
    if( !pPage ){
      rc = LSM_NOMEM_BKPT;
    }else{
      pPage->aData = (u8 *)lsmMalloc(pFS->pEnv, pFS->nPagesize);

      if( !pPage->aData ){
        lsmFree(pFS->pEnv, pPage);
        rc = LSM_NOMEM_BKPT;
        pPage = 0;
      }
      pFS->nCacheAlloc++;
    }
  }else{
    u8 *aData;
    pPage = pFS->pLruFirst;
    aData = pPage->aData;
    fsPageRemoveFromLru(pFS, pPage);
    fsPageRemoveFromHash(pFS, pPage);

    memset(pPage, 0, sizeof(Page));

    pPage->aData = aData;
  }

  if( pPage ){
    pPage->flags = PAGE_FREE;
  }
  *ppOut = pPage;
  return rc;
}











static void fsGrowMapping(
  FileSystem *pFS,
  i64 iSz,
  int *pRc
){
  /* This function won't work with compressed databases yet. */
  assert( pFS->pCompress==0 );
  assert( PAGE_HASPREV==4 );

  if( *pRc==LSM_OK && iSz>pFS->nMap ){
    int rc;
    u8 *aOld = pFS->pMap;
    rc = lsmEnvRemap(pFS->pEnv, pFS->fdDb, iSz, &pFS->pMap, &pFS->nMap);
    if( rc==LSM_OK && pFS->pMap!=aOld ){
      Page *pFix;
      i64 iOff = (u8 *)pFS->pMap - aOld;
      for(pFix=pFS->pMapped; pFix; pFix=pFix->pMappedNext){
        pFix->aData += iOff;
      }
      lsmSortedRemap(pFS->pDb);
    }
    *pRc = rc;
  }
}


/*
** fsync() the database file.
*/
int lsmFsSyncDb(FileSystem *pFS, int nBlock){
#if 0
  if( nBlock && pFS->bUseMmap ){
    int rc = LSM_OK;
    i64 nMin = (i64)nBlock * (i64)pFS->nBlocksize;
    fsGrowMapping(pFS, nMin, &rc);
    if( rc!=LSM_OK ) return rc;
  }
#endif
  return lsmEnvSync(pFS->pEnv, pFS->fdDb);
}

static int fsPageGet(FileSystem *, Segment *, Pgno, int, Page **, int *);

static int fsRedirectBlock(Redirect *p, int iBlk){
  if( p ){

  
  if( pSeg ){
    iRead = fsRedirectBlock(pSeg->pRedirect, iBlock);
  }else{
    iRead = iBlock;
  }

  assert( pFS->nMapLimit==0 || pFS->pCompress==0 );
  if( pFS->pCompress ){
    i64 iOff;                     /* File offset to read data from */
    u8 aNext[4];                  /* 4-byte pointer read from db file */

    iOff = (i64)iRead * pFS->nBlocksize - sizeof(aNext);
    rc = lsmEnvRead(pFS->pEnv, pFS->fdDb, iOff, aNext, sizeof(aNext));
    if( rc==LSM_OK ){

  FileSystem *pFS,                /* File-system object handle */
  Segment *pSeg,                  /* Use this segment for block redirects */
  int iBlock,                     /* Read field from this block */
  int *piPrev                     /* OUT: Previous block in linked list */
){
  int rc = LSM_OK;                /* Return code */

  assert( pFS->nMapLimit==0 || pFS->pCompress==0 );
  assert( iBlock>0 );

  if( pFS->pCompress ){
    i64 iOff = fsFirstPageOnBlock(pFS, iBlock) - 4;
    u8 aPrev[4];                  /* 4-byte pointer read from db file */
    rc = lsmEnvRead(pFS->pEnv, pFS->fdDb, iOff, aPrev, sizeof(aPrev));
    if( rc==LSM_OK ){

  int rc = LSM_OK;

  /* In most cases iReal is the same as iPg. Except, if pSeg->pRedirect is 
  ** not NULL, and the block containing iPg has been redirected, then iReal
  ** is the page number after redirection.  */
  Pgno iReal = lsmFsRedirectPage(pFS, (pSeg ? pSeg->pRedirect : 0), iPg);

  assert_lists_are_ok(pFS);
  assert( iPg>=fsFirstPageOnBlock(pFS, 1) );
  assert( iReal>=fsFirstPageOnBlock(pFS, 1) );
  *ppPg = 0;


  /* Search the hash-table for the page */
  p = fsPageFindInHash(pFS, iReal, &iHash);

  if( p ){
    assert( p->flags & PAGE_FREE );
    if( p->nRef==0 ) fsPageRemoveFromLru(pFS, p);
  }else{

    if( fsMmapPage(pFS, iReal) ){
      i64 iEnd = (i64)iReal * pFS->nPagesize;
      fsGrowMapping(pFS, iEnd, &rc);
      if( rc!=LSM_OK ) return rc;











      if( pFS->pFree ){
        p = pFS->pFree;
        pFS->pFree = p->pFreeNext;
        assert( p->nRef==0 );
      }else{
        p = lsmMallocZeroRc(pFS->pEnv, sizeof(Page), &rc);
        if( rc ) return rc;

        p->pFS = pFS;
      }
      p->aData = &((u8 *)pFS->pMap)[pFS->nPagesize * (iReal-1)];
      p->iPg = iReal;



      /* This page now carries a pointer to the mapping. Link it in to
      ** the FileSystem.pMapped list.  */
      assert( p->pMappedNext==0 );
      p->pMappedNext = pFS->pMapped;
      pFS->pMapped = p;


      assert( pFS->pCompress==0 );
      assert( (p->flags & PAGE_FREE)==0 );
    }else{
      rc = fsPageBuffer(pFS, &p);
      if( rc==LSM_OK ){
        int nSpace = 0;
        p->iPg = iReal;
        p->nRef = 0;
        p->pFS = pFS;
        assert( p->flags==0 || p->flags==PAGE_FREE );

            i64 iOff = (i64)(iReal-1) * pFS->nPagesize;
            rc = lsmEnvRead(pFS->pEnv, pFS->fdDb, iOff, p->aData, nByte);
          }
          pFS->nRead++;
        }

        /* If the xRead() call was successful (or not attempted), link the
        ** page into the page-cache hash-table. Otherwise, if it failed,
        ** free the buffer. */
        if( rc==LSM_OK && nSpace==0 ){
          p->pHashNext = pFS->apHash[iHash];
          pFS->apHash[iHash] = p;
        }else{
          fsPageBufferFree(p);
          p = 0;
          if( pnSpace ) *pnSpace = nSpace;
        }
      }


    }

    assert( (rc==LSM_OK && (p || (pnSpace && *pnSpace)))
         || (rc!=LSM_OK && p==0) 
    );
  }

** may be garbage. It is the callers responsibility to deal with this.
*/
int lsmFsReadSyncedId(lsm_db *db, int iMeta, i64 *piVal){
  FileSystem *pFS = db->pFS;
  int rc = LSM_OK;

  assert( iMeta==1 || iMeta==2 );
  if( pFS->nMapLimit>0 ){
    fsGrowMapping(pFS, iMeta*LSM_META_PAGE_SIZE, &rc);
    if( rc==LSM_OK ){
      *piVal = (i64)lsmGetU64(&((u8 *)pFS->pMap)[(iMeta-1)*LSM_META_PAGE_SIZE]);
    }
  }else{
    MetaPage *pMeta = 0;
    rc = lsmFsMetaPageGet(pFS, 0, iMeta, &pMeta);

  MetaPage *pPg;
  assert( iPg==1 || iPg==2 );

  pPg = lsmMallocZeroRc(pFS->pEnv, sizeof(Page), &rc);

  if( pPg ){
    i64 iOff = (iPg-1) * pFS->nMetasize;
    if( pFS->nMapLimit>0 ){
      fsGrowMapping(pFS, 2*pFS->nMetasize, &rc);
      pPg->aData = (u8 *)(pFS->pMap) + iOff;
    }else{
      pPg->aData = lsmMallocRc(pFS->pEnv, pFS->nMetasize, &rc);
      if( rc==LSM_OK && bWrite==0 ){
        rc = lsmEnvRead(pFS->pEnv, pFS->fdDb, iOff, pPg->aData, pFS->nMetasize);
      }
#ifndef NDEBUG
      /* pPg->aData causes an uninitialized access via a downstreadm write().
         After discussion on this list, this memory should not, for performance
         reasons, be memset. However, tracking down "real" misuse is more
         difficult with this "false" positive, so it is set when NDEBUG.
      */
      else if( rc==LSM_OK ){
        memset( pPg->aData, 0x77, pFS->nMetasize );
      }
#endif
    }

    if( rc!=LSM_OK ){
      if( pFS->nMapLimit==0 ) lsmFree(pFS->pEnv, pPg->aData);
      lsmFree(pFS->pEnv, pPg);
      pPg = 0;
    }else{
      pPg->iPg = iPg;
      pPg->bWrite = bWrite;
      pPg->pFS = pFS;
    }

** Release a meta-page reference obtained via a call to lsmFsMetaPageGet().
*/
int lsmFsMetaPageRelease(MetaPage *pPg){
  int rc = LSM_OK;
  if( pPg ){
    FileSystem *pFS = pPg->pFS;

    if( pFS->nMapLimit==0 ){
      if( pPg->bWrite ){
        i64 iOff = (pPg->iPg==2 ? pFS->nMetasize : 0);
        int nWrite = pFS->nMetasize;
        rc = lsmEnvWrite(pFS->pEnv, pFS->fdDb, iOff, pPg->aData, nWrite);
      }
      lsmFree(pFS->pEnv, pPg->aData);
    }

** It is safe to assume that there are no outstanding references to pages 
** on block iTo. And that block iFrom is not currently being written. In
** other words, the data can be read and written directly.
*/
int lsmFsMoveBlock(FileSystem *pFS, Segment *pSeg, int iTo, int iFrom){
  Snapshot *p = pFS->pDb->pWorker;
  int rc = LSM_OK;
  i64 nMap;

  i64 iFromOff = (i64)(iFrom-1) * pFS->nBlocksize;
  i64 iToOff = (i64)(iTo-1) * pFS->nBlocksize;
  
  assert( iTo!=1 );
  assert( iFrom>iTo );

  /* Grow the mapping as required. */
  nMap = LSM_MIN(pFS->nMapLimit, (i64)iFrom * pFS->nBlocksize);
  fsGrowMapping(pFS, nMap, &rc);







  if( rc==LSM_OK ){
    const int nPagePerBlock = (pFS->nBlocksize / pFS->nPagesize);
    int nSz = pFS->nPagesize;
    int i;
    u8 *aBuf = 0;
    u8 *aData = 0;

    for(i=0; rc==LSM_OK && i<nPagePerBlock; i++){
      i64 iOff = iFromOff + i*nSz;
      Page *pPg;

      /* Set aData to point to a buffer containing the from page */
      if( (iOff+nSz)<=pFS->nMapLimit ){
        u8 *aMap = (u8 *)(pFS->pMap);
        aData = &aMap[iOff];
      }else{
        if( aBuf==0 ){
          aBuf = (u8 *)lsmMallocRc(pFS->pEnv, nSz, &rc);
          if( aBuf==0 ) break;
        }
        aData = aBuf;
        rc = lsmEnvRead(pFS->pEnv, pFS->fdDb, iOff, aData, nSz);
      }

      /* Copy aData to the to page */
      if( rc==LSM_OK ){
        iOff = iToOff + i*nSz;
        if( (iOff+nSz)<=pFS->nMapLimit ){
          u8 *aMap = (u8 *)(pFS->pMap);
          memcpy(&aMap[iOff], aData, nSz);
        }else{
          rc = lsmEnvWrite(pFS->pEnv, pFS->fdDb, iOff, aData, nSz);
        }
      }

    }
    lsmFree(pFS->pEnv, aBuf);
    lsmFsPurgeCache(pFS);
  }

  /* Update append-point list if necessary */
  if( rc==LSM_OK ){
    int i;
    for(i=0; i<LSM_APPLIST_SZ; i++){
      if( fsPageToBlock(pFS, p->aiAppend[i])==iFrom ){

  int rc = *pRc;
  Page *pPg;

  pPg = pFS->pWaiting;
  pFS->pWaiting = 0;

  while( pPg ){
    Page *pNext = pPg->pWaitingNext;
    if( rc==LSM_OK ) rc = lsmFsPagePersist(pPg);
    assert( pPg->nRef==1 );
    lsmFsPageRelease(pPg);
    pPg = pNext;
  }
  *pRc = rc;
}

static void fsRemoveHashEntry(FileSystem *pFS, Pgno iPg){
  Page *p;
  int iHash = fsHashKey(pFS->nHash, iPg);

  for(p=pFS->apHash[iHash]; p && p->iPg!=iPg; p=p->pHashNext);

  if( p ){
    assert( p->nRef==0 || (p->flags & PAGE_FREE)==0 );
    fsPageRemoveFromHash(pFS, p);
    p->iPg = 0;
    iHash = fsHashKey(pFS->nHash, 0);
    p->pHashNext = pFS->apHash[iHash];
    pFS->apHash[iHash] = p;
  }
}

        ** lsmFsPagePersist() to write an out-of-order page. Instead a page 
        ** number is assigned here so that the page data will be appended
        ** to the current segment.
        */
        Page **pp;
        int iPrev = 0;
        int iNext = 0;
        int iHash;

        assert( pPg->pSeg->iFirst );
        assert( pPg->flags & PAGE_FREE );
        assert( (pPg->flags & PAGE_HASPREV)==0 );
        assert( pPg->nData==pFS->nPagesize-4 );

        rc = fsAppendPage(pFS, pPg->pSeg, &pPg->iPg, &iPrev, &iNext);
        if( rc!=LSM_OK ) return rc;

        assert( pPg->flags & PAGE_FREE );
        iHash = fsHashKey(pFS->nHash, pPg->iPg);
        fsRemoveHashEntry(pFS, pPg->iPg);
        pPg->pHashNext = pFS->apHash[iHash];
        pFS->apHash[iHash] = pPg;
        assert( pPg->pHashNext==0 || pPg->pHashNext->iPg!=pPg->iPg );


        if( iPrev ){
          assert( iNext==0 );
          memmove(&pPg->aData[4], pPg->aData, pPg->nData);
          lsmPutU32(pPg->aData, iPrev);
          pPg->flags |= PAGE_HASPREV;
          pPg->aData += 4;
        }else if( iNext ){
          assert( iPrev==0 );
          lsmPutU32(&pPg->aData[pPg->nData], iNext);
        }else{
          int nData = pPg->nData;
          pPg->nData += 4;
          lsmSortedExpandBtreePage(pPg, nData);
        }

        pPg->nRef++;
        for(pp=&pFS->pWaiting; *pp; pp=&(*pp)->pWaitingNext);
        *pp = pPg;
        assert( pPg->pWaitingNext==0 );

      }else{
        i64 iOff;                   /* Offset to write within database file */

        iOff = (i64)pFS->nPagesize * (i64)(pPg->iPg-1);
        if( fsMmapPage(pFS, pPg->iPg)==0 ){
          u8 *aData = pPg->aData - (pPg->flags & PAGE_HASPREV);
          rc = lsmEnvWrite(pFS->pEnv, pFS->fdDb, iOff, aData, pFS->nPagesize);
        }else if( pPg->flags & PAGE_FREE ){
          fsGrowMapping(pFS, iOff + pFS->nPagesize, &rc);
          if( rc==LSM_OK ){
            u8 *aTo = &((u8 *)(pFS->pMap))[iOff];
            u8 *aFrom = pPg->aData - (pPg->flags & PAGE_HASPREV);
            memcpy(aTo, aFrom, pFS->nPagesize);
            lsmFree(pFS->pEnv, aFrom);
            pFS->nCacheAlloc--;
            pPg->aData = aTo + (pPg->flags & PAGE_HASPREV);
            pPg->flags &= ~PAGE_FREE;
            fsPageRemoveFromHash(pFS, pPg);
            pPg->pMappedNext = pFS->pMapped;
            pFS->pMapped = pPg;
          }
        }

        lsmFsFlushWaiting(pFS, &rc);
        pPg->flags &= ~PAGE_DIRTY;
        pFS->nWrite++;
      }

      assert( pPg->pFS->pCompress 
           || fsIsFirst(pPg->pFS, pPg->iPg)==0 
           || (pPg->flags & PAGE_HASPREV)
      );
      pPg->aData -= (pPg->flags & PAGE_HASPREV);
      pPg->flags &= ~PAGE_HASPREV;

      if( (pPg->flags & PAGE_FREE)==0 ){
        /* Removed from mapped list */
        Page **pp;
        for(pp=&pFS->pMapped; (*pp)!=pPg; pp=&(*pp)->pMappedNext);
        *pp = pPg->pMappedNext;
        pPg->pMappedNext = 0;

        /* Add to free list */
        pPg->pFreeNext = pFS->pFree;
        pFS->pFree = pPg;
      }else{
#if 0
        assert( pPg->pLruNext==0 );
        assert( pPg->pLruPrev==0 );
        fsPageRemoveFromHash(pFS, pPg);
        fsPageBufferFree(pPg);

  pDb->nDfltBlksz = LSM_DFLT_BLOCK_SIZE;
  pDb->nMerge = LSM_DFLT_AUTOMERGE;
  pDb->nMaxFreelist = LSM_MAX_FREELIST_ENTRIES;
  pDb->bUseLog = LSM_DFLT_USE_LOG;
  pDb->iReader = -1;
  pDb->iRwclient = -1;
  pDb->bMultiProc = LSM_DFLT_MULTIPLE_PROCESSES;
  pDb->iMmap = LSM_DFLT_MMAP;
  pDb->xLog = xLog;
  pDb->compress.iId = LSM_COMPRESSION_NONE;
  return LSM_OK;
}

lsm_env *lsm_get_env(lsm_db *pDb){
  assert( pDb->pEnv );

      }
      *piVal = pDb->eSafety;
      break;
    }

    case LSM_CONFIG_MMAP: {
      int *piVal = va_arg(ap, int *);
      if( pDb->iReader<0 && *piVal>=0 ){
        pDb->iMmap = *piVal;
        rc = lsmFsConfigure(pDb);
      }
      *piVal = pDb->iMmap;
      break;
    }

    case LSM_CONFIG_USE_LOG: {
      int *piVal = va_arg(ap, int *);
      if( pDb->nTransOpen==0 && (*piVal==0 || *piVal==1) ){
        pDb->bUseLog = *piVal;

  }

  /* If the db handle is read-write, then connect to the system now. Run
  ** recovery as necessary. Or, if this is a read-only database handle,
  ** defer attempting to connect to the system until a read-transaction
  ** is opened.  */
  if( pDb->bReadonly==0 ){



    if( rc==LSM_OK ){
      rc = lsmFsConfigure(pDb);
    }
    if( rc==LSM_OK ){
      rc = doDbConnect(pDb);
    }
  }

  return rc;
}

static void dbDeferClose(lsm_db *pDb){
  if( pDb->pFS ){

    bOld = (lsmTreeHasOld(pDb) && pDb->treehdr.iOldLog!=pDb->pClient->iLogOff);
    if( !bOld && pCsr->apTreeCsr[1] ){
      lsmTreeCursorDestroy(pCsr->apTreeCsr[1]);
      pCsr->apTreeCsr[1] = 0;
    }else if( bOld && !pCsr->apTreeCsr[1] ){
      rc = lsmTreeCursorNew(pDb, 1, &pCsr->apTreeCsr[1]);
    }

    pCsr->flags = (CURSOR_IGNORE_SYSTEM | CURSOR_IGNORE_DELETE);

  }else{
    pCsr = multiCursorNew(pDb, &rc);
    if( rc==LSM_OK ) rc = multiCursorInit(pCsr, pDb->pClient);
  }

  if( rc!=LSM_OK ){

  lsm_i64 *pnOut
){
  off_t iSz;
  int prc;
  PosixFile *p = (PosixFile *)pFile;
  struct stat buf;

  /* If the file is between 0 and 2MB in size, extend it in chunks of 256K.
  ** Thereafter, in chunks of 1MB at a time.  */
  const int aIncrSz[] = {256*1024, 1024*1024};
  int nIncrSz = aIncrSz[iMin>(2*1024*1024)];

  if( p->pMap ){
    munmap(p->pMap, p->nMap);
    *ppOut = p->pMap = 0;
    *pnOut = p->nMap = 0;
  }

  if( iMin>=0 ){
    memset(&buf, 0, sizeof(buf));
    prc = fstat(p->fd, &buf);
    if( prc!=0 ) return LSM_IOERR_BKPT;
    iSz = buf.st_size;
    if( iSz<iMin ){
      iSz = ((iMin + nIncrSz-1) / nIncrSz) * nIncrSz;
      prc = ftruncate(p->fd, iSz);
      if( prc!=0 ) return LSM_IOERR_BKPT;
    }

    p->pMap = mmap(0, iSz, PROT_READ|PROT_WRITE, MAP_SHARED, p->fd, 0);
    p->nMap = iSz;
  }

reset_db
do_test 2.0 { sqlite4_lsm_config db main safety   2    } {2}

do_execsql_test 2.2 {
  CREATE TABLE t1(a PRIMARY KEY, b);
  INSERT INTO t1 VALUES(randstr(50,50), randstr(50,50));
} {}
do_filesize_test 2.3   262144 1024

do_execsql_test 2.4 {
  BEGIN;
    INSERT INTO t1 VALUES(randstr(50,50), randstr(50,50));
    INSERT INTO t1 VALUES(randstr(50,50), randstr(50,50));
    INSERT INTO t1 VALUES(randstr(50,50), randstr(50,50));
    INSERT INTO t1 VALUES(randstr(50,50), randstr(50,50));
    INSERT INTO t1 VALUES(randstr(50,50), randstr(50,50));
    INSERT INTO t1 VALUES(randstr(50,50), randstr(50,50));
  COMMIT;
} {}
do_filesize_test 2.5   262144 2048

do_test         2.6 { optimize_db } {}
do_execsql_test 2.7 { INSERT INTO t1 VALUES(randstr(50,50), randstr(50,50)) }
do_test         2.8 { sqlite4_lsm_checkpoint db main } {}
do_test 2.9 { sqlite4_lsm_info db main log-structure } {0 0 0 0 2560 3072}

for {set i 1} {$i <= 6} {incr i} {

set testprefix lsm5
db close

# Create a new database with file name $file.
#
proc create_abc_db {file} {
  forcedelete $file
  lsm_open db $file {block_size 256 mmap 0}
  db write a alpha
  db write b bravo
  db write c charlie
  db close
}

proc create_abc_log {file} {
  forcedelete $file ${file}-2
  lsm_open db ${file}-2 {mmap 0}
  db write a alpha
  db write b bravo
  db write c charlie
  file copy ${file}-2 $file
  file copy ${file}-2-log $file-log
  db close
}

#-------------------------------------------------------------------------
# When the database system is shut down (i.e. when the last connection
# disconnects), an attempt is made to truncate the database file to the
# minimum number of blocks required.
# 
# This test case checks that this process does not actually cause the
# database to grow.
# 
do_test 1.1 {
  lsm_open db test.db {mmap 0}

} {db}
do_test 1.2 {
  db write 1 one
  db write 2 two
  db close
} {}
do_test 1.3 {
  expr [file size test.db] < (64*1024)

  # Test that connection 2 can see changes made by connection 1.
  do_test 1.$tn.1 { 
    sql1 { CREATE TABLE t1(a PRIMARY KEY, b) } 
    sql1 { INSERT INTO t1 VALUES(1, 2) }
    sql2 { SELECT * FROM t1 }
  } {1 2}

  do_test 1.$tn.2 { file size test.db } [expr 256*1024]

  # Connection 1 does not see uncommitted changes made by connection 2.
  do_test 1.$tn.3 {
    sql2 { BEGIN; INSERT INTO t1 VALUES(2, 4); }
    sql1 { SELECT * FROM t1 }
  } {1 2}

  # But it can from a new snapshot.
  do_test 1.$tn.9 {
    sql1  { COMMIT; BEGIN }
    sql1  { INSERT INTO t1 VALUES(6, 12) }
    sql1  { SELECT * FROM t1 }
  } {1 2 2 4 3 6 4 8 5 10 6 12}

  do_test 1.$tn.10 { file size test.db } [expr 256*1024]
}

finish_test

  INSERT INTO t1 SELECT randomblob(1024) FROM t1;    --  64
}
do_execsql_test 71.2 { SELECT count(*) FROM t1 } 64
db close
sqlite4 db test.db
do_execsql_test 71.3 { SELECT count(*) FROM t1 } 64
do_test 71.4 { 
  expr {[file size test.db] <= 256*1024}
} {1}

#-------------------------------------------------------------------------
# This is testing that the "phantom" runs feature works with mmap.
#
# UPDATE: Said feature was dropped early in development. But the test 
# remains valid.