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SQLite training in Houston TX on 2019-11-05 (details)
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Overview
Comment:Reorder the fields in the VdbeCursor object so that those that need to be bulk zeroed on allocation are grouped at the beginning, and the memset() only runs over those fields that really need it.
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SHA1: 8165f88bb1d40693d67005a8d5dc499085f64b91
User & Date: drh 2016-12-10 12:58:15
Context
2016-12-10
13:12
Avoid an unnecessary memset() in the sqlite3BtreeInsert() routine. check-in: 35ecd4eb user: drh tags: trunk
12:58
Reorder the fields in the VdbeCursor object so that those that need to be bulk zeroed on allocation are grouped at the beginning, and the memset() only runs over those fields that really need it. check-in: 8165f88b user: drh tags: trunk
04:06
Avoid signed integer overflow when dealing with a LIMIT and OFFSET whose sum exceeds the maximum integer value. check-in: c9bdf7ad user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/vdbe.c.

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  assert( iCur>=0 && iCur<p->nCursor );
  if( p->apCsr[iCur] ){ /*OPTIMIZATION-IF-FALSE*/
    sqlite3VdbeFreeCursor(p, p->apCsr[iCur]);
    p->apCsr[iCur] = 0;
  }
  if( SQLITE_OK==sqlite3VdbeMemClearAndResize(pMem, nByte) ){
    p->apCsr[iCur] = pCx = (VdbeCursor*)pMem->z;
    memset(pCx, 0, sizeof(VdbeCursor));
    pCx->eCurType = eCurType;
    pCx->iDb = iDb;
    pCx->nField = nField;
    pCx->aOffset = &pCx->aType[nField];
    if( eCurType==CURTYPE_BTREE ){
      pCx->uc.pCursor = (BtCursor*)
          &pMem->z[ROUND8(sizeof(VdbeCursor))+2*sizeof(u32)*nField];
................................................................................
      SQLITE_OPEN_TRANSIENT_DB;
  assert( pOp->p1>=0 );
  assert( pOp->p2>=0 );
  pCx = allocateCursor(p, pOp->p1, pOp->p2, -1, CURTYPE_BTREE);
  if( pCx==0 ) goto no_mem;
  pCx->nullRow = 1;
  pCx->isEphemeral = 1;
  rc = sqlite3BtreeOpen(db->pVfs, 0, db, &pCx->pBt, 
                        BTREE_OMIT_JOURNAL | BTREE_SINGLE | pOp->p5, vfsFlags);
  if( rc==SQLITE_OK ){
    rc = sqlite3BtreeBeginTrans(pCx->pBt, 1);
  }
  if( rc==SQLITE_OK ){
    /* If a transient index is required, create it by calling
    ** sqlite3BtreeCreateTable() with the BTREE_BLOBKEY flag before
    ** opening it. If a transient table is required, just use the
    ** automatically created table with root-page 1 (an BLOB_INTKEY table).
    */
    if( (pKeyInfo = pOp->p4.pKeyInfo)!=0 ){
      int pgno;
      assert( pOp->p4type==P4_KEYINFO );
      rc = sqlite3BtreeCreateTable(pCx->pBt, &pgno, BTREE_BLOBKEY | pOp->p5); 
      if( rc==SQLITE_OK ){
        assert( pgno==MASTER_ROOT+1 );
        assert( pKeyInfo->db==db );
        assert( pKeyInfo->enc==ENC(db) );
        pCx->pKeyInfo = pKeyInfo;
        rc = sqlite3BtreeCursor(pCx->pBt, pgno, BTREE_WRCSR,
                                pKeyInfo, pCx->uc.pCursor);
      }
      pCx->isTable = 0;
    }else{
      rc = sqlite3BtreeCursor(pCx->pBt, MASTER_ROOT, BTREE_WRCSR,
                              0, pCx->uc.pCursor);
      pCx->isTable = 1;
    }
  }
  if( rc ) goto abort_due_to_error;
  pCx->isOrdered = (pOp->p5!=BTREE_UNORDERED);
  break;







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  assert( iCur>=0 && iCur<p->nCursor );
  if( p->apCsr[iCur] ){ /*OPTIMIZATION-IF-FALSE*/
    sqlite3VdbeFreeCursor(p, p->apCsr[iCur]);
    p->apCsr[iCur] = 0;
  }
  if( SQLITE_OK==sqlite3VdbeMemClearAndResize(pMem, nByte) ){
    p->apCsr[iCur] = pCx = (VdbeCursor*)pMem->z;
    memset(pCx, 0, offsetof(VdbeCursor,pAltCursor));
    pCx->eCurType = eCurType;
    pCx->iDb = iDb;
    pCx->nField = nField;
    pCx->aOffset = &pCx->aType[nField];
    if( eCurType==CURTYPE_BTREE ){
      pCx->uc.pCursor = (BtCursor*)
          &pMem->z[ROUND8(sizeof(VdbeCursor))+2*sizeof(u32)*nField];
................................................................................
      SQLITE_OPEN_TRANSIENT_DB;
  assert( pOp->p1>=0 );
  assert( pOp->p2>=0 );
  pCx = allocateCursor(p, pOp->p1, pOp->p2, -1, CURTYPE_BTREE);
  if( pCx==0 ) goto no_mem;
  pCx->nullRow = 1;
  pCx->isEphemeral = 1;
  rc = sqlite3BtreeOpen(db->pVfs, 0, db, &pCx->pBtx, 
                        BTREE_OMIT_JOURNAL | BTREE_SINGLE | pOp->p5, vfsFlags);
  if( rc==SQLITE_OK ){
    rc = sqlite3BtreeBeginTrans(pCx->pBtx, 1);
  }
  if( rc==SQLITE_OK ){
    /* If a transient index is required, create it by calling
    ** sqlite3BtreeCreateTable() with the BTREE_BLOBKEY flag before
    ** opening it. If a transient table is required, just use the
    ** automatically created table with root-page 1 (an BLOB_INTKEY table).
    */
    if( (pCx->pKeyInfo = pKeyInfo = pOp->p4.pKeyInfo)!=0 ){
      int pgno;
      assert( pOp->p4type==P4_KEYINFO );
      rc = sqlite3BtreeCreateTable(pCx->pBtx, &pgno, BTREE_BLOBKEY | pOp->p5); 
      if( rc==SQLITE_OK ){
        assert( pgno==MASTER_ROOT+1 );
        assert( pKeyInfo->db==db );
        assert( pKeyInfo->enc==ENC(db) );

        rc = sqlite3BtreeCursor(pCx->pBtx, pgno, BTREE_WRCSR,
                                pKeyInfo, pCx->uc.pCursor);
      }
      pCx->isTable = 0;
    }else{
      rc = sqlite3BtreeCursor(pCx->pBtx, MASTER_ROOT, BTREE_WRCSR,
                              0, pCx->uc.pCursor);
      pCx->isTable = 1;
    }
  }
  if( rc ) goto abort_due_to_error;
  pCx->isOrdered = (pOp->p5!=BTREE_UNORDERED);
  break;

Changes to src/vdbeInt.h.

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**          -  On either an index or a table
**      * A sorter
**      * A virtual table
**      * A one-row "pseudotable" stored in a single register
*/
typedef struct VdbeCursor VdbeCursor;
struct VdbeCursor {
  u8 eCurType;          /* One of the CURTYPE_* values above */
  i8 iDb;               /* Index of cursor database in db->aDb[] (or -1) */
  u8 nullRow;           /* True if pointing to a row with no data */
  u8 deferredMoveto;    /* A call to sqlite3BtreeMoveto() is needed */
  u8 isTable;           /* True for rowid tables.  False for indexes */
#ifdef SQLITE_DEBUG
  u8 seekOp;            /* Most recent seek operation on this cursor */
  u8 wrFlag;            /* The wrFlag argument to sqlite3BtreeCursor() */
#endif
  Bool isEphemeral:1;   /* True for an ephemeral table */
  Bool useRandomRowid:1;/* Generate new record numbers semi-randomly */
  Bool isOrdered:1;     /* True if the table is not BTREE_UNORDERED */
  Pgno pgnoRoot;        /* Root page of the open btree cursor */
  i16 nField;           /* Number of fields in the header */
  u16 nHdrParsed;       /* Number of header fields parsed so far */















  union {
    BtCursor *pCursor;          /* CURTYPE_BTREE.  Btree cursor */
    sqlite3_vtab_cursor *pVCur; /* CURTYPE_VTAB.   Vtab cursor */
    int pseudoTableReg;         /* CURTYPE_PSEUDO. Reg holding content. */
    VdbeSorter *pSorter;        /* CURTYPE_SORTER. Sorter object */
  } uc;
  Btree *pBt;           /* Separate file holding temporary table */
  KeyInfo *pKeyInfo;    /* Info about index keys needed by index cursors */

  int seekResult;       /* Result of previous sqlite3BtreeMoveto() or 0
                        ** if there have been no prior seeks on the cursor. */
  /* NB: seekResult does not distinguish between "no seeks have ever occurred
  ** on this cursor" and "the most recent seek was an exact match". */
  i64 seqCount;         /* Sequence counter */
  i64 movetoTarget;     /* Argument to the deferred sqlite3BtreeMoveto() */


  VdbeCursor *pAltCursor; /* Associated index cursor from which to read */
  int *aAltMap;           /* Mapping from table to index column numbers */
#ifdef SQLITE_ENABLE_COLUMN_USED_MASK
  u64 maskUsed;         /* Mask of columns used by this cursor */
#endif

  /* Cached information about the header for the data record that the
  ** cursor is currently pointing to.  Only valid if cacheStatus matches
  ** Vdbe.cacheCtr.  Vdbe.cacheCtr will never take on the value of
  ** CACHE_STALE and so setting cacheStatus=CACHE_STALE guarantees that
  ** the cache is out of date.
  **
  ** aRow might point to (ephemeral) data for the current row, or it might
  ** be NULL.
  */
  u32 cacheStatus;      /* Cache is valid if this matches Vdbe.cacheCtr */
  u32 payloadSize;      /* Total number of bytes in the record */
  u32 szRow;            /* Byte available in aRow */
  u32 iHdrOffset;       /* Offset to next unparsed byte of the header */
  const u8 *aRow;       /* Data for the current row, if all on one page */
  u32 *aOffset;         /* Pointer to aType[nField] */
  u32 aType[1];         /* Type values for all entries in the record */
  /* 2*nField extra array elements allocated for aType[], beyond the one
  ** static element declared in the structure.  nField total array slots for
  ** aType[] and nField+1 array slots for aOffset[] */

};


/*
** A value for VdbeCursor.cacheStatus that means the cache is always invalid.
*/
#define CACHE_STALE 0







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**          -  On either an index or a table
**      * A sorter
**      * A virtual table
**      * A one-row "pseudotable" stored in a single register
*/
typedef struct VdbeCursor VdbeCursor;
struct VdbeCursor {
  u8 eCurType;            /* One of the CURTYPE_* values above */
  i8 iDb;                 /* Index of cursor database in db->aDb[] (or -1) */
  u8 nullRow;             /* True if pointing to a row with no data */
  u8 deferredMoveto;      /* A call to sqlite3BtreeMoveto() is needed */
  u8 isTable;             /* True for rowid tables.  False for indexes */
#ifdef SQLITE_DEBUG
  u8 seekOp;              /* Most recent seek operation on this cursor */
  u8 wrFlag;              /* The wrFlag argument to sqlite3BtreeCursor() */
#endif
  Bool isEphemeral:1;     /* True for an ephemeral table */
  Bool useRandomRowid:1;  /* Generate new record numbers semi-randomly */
  Bool isOrdered:1;       /* True if the table is not BTREE_UNORDERED */
  Btree *pBtx;            /* Separate file holding temporary table */
  i64 seqCount;           /* Sequence counter */
  int *aAltMap;           /* Mapping from table to index column numbers */

  /* Cached OP_Column parse information is only valid if cacheStatus matches
  ** Vdbe.cacheCtr.  Vdbe.cacheCtr will never take on the value of
  ** CACHE_STALE (0) and so setting cacheStatus=CACHE_STALE guarantees that
  ** the cache is out of date. */
  u32 cacheStatus;        /* Cache is valid if this matches Vdbe.cacheCtr */
  int seekResult;         /* Result of previous sqlite3BtreeMoveto() or 0
                          ** if there have been no prior seeks on the cursor. */
  /* NB: seekResult does not distinguish between "no seeks have ever occurred
  ** on this cursor" and "the most recent seek was an exact match". */

  /* When a new VdbeCursor is allocated, only the fields above are zeroed.
  ** The fields that follow are uninitialized, and must be individually
  ** initialized prior to first use. */
  VdbeCursor *pAltCursor; /* Associated index cursor from which to read */
  union {
    BtCursor *pCursor;          /* CURTYPE_BTREE.  Btree cursor */
    sqlite3_vtab_cursor *pVCur; /* CURTYPE_VTAB.   Vtab cursor */
    int pseudoTableReg;         /* CURTYPE_PSEUDO. Reg holding content. */
    VdbeSorter *pSorter;        /* CURTYPE_SORTER. Sorter object */
  } uc;

  KeyInfo *pKeyInfo;      /* Info about index keys needed by index cursors */
  u32 iHdrOffset;         /* Offset to next unparsed byte of the header */
  Pgno pgnoRoot;          /* Root page of the open btree cursor */
  i16 nField;             /* Number of fields in the header */
  u16 nHdrParsed;         /* Number of header fields parsed so far */


  i64 movetoTarget;       /* Argument to the deferred sqlite3BtreeMoveto() */
  u32 *aOffset;           /* Pointer to aType[nField] */
  const u8 *aRow;         /* Data for the current row, if all on one page */
  u32 payloadSize;        /* Total number of bytes in the record */
  u32 szRow;              /* Byte available in aRow */
#ifdef SQLITE_ENABLE_COLUMN_USED_MASK
  u64 maskUsed;           /* Mask of columns used by this cursor */
#endif

















  /* 2*nField extra array elements allocated for aType[], beyond the one
  ** static element declared in the structure.  nField total array slots for
  ** aType[] and nField+1 array slots for aOffset[] */
  u32 aType[1];           /* Type values record decode.  MUST BE LAST */
};


/*
** A value for VdbeCursor.cacheStatus that means the cache is always invalid.
*/
#define CACHE_STALE 0

Changes to src/vdbeaux.c.

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** Close a VDBE cursor and release all the resources that cursor 
** happens to hold.
*/
void sqlite3VdbeFreeCursor(Vdbe *p, VdbeCursor *pCx){
  if( pCx==0 ){
    return;
  }
  assert( pCx->pBt==0 || pCx->eCurType==CURTYPE_BTREE );
  switch( pCx->eCurType ){
    case CURTYPE_SORTER: {
      sqlite3VdbeSorterClose(p->db, pCx);
      break;
    }
    case CURTYPE_BTREE: {
      if( pCx->pBt ){
        sqlite3BtreeClose(pCx->pBt);
        /* The pCx->pCursor will be close automatically, if it exists, by
        ** the call above. */
      }else{
        assert( pCx->uc.pCursor!=0 );
        sqlite3BtreeCloseCursor(pCx->uc.pCursor);
      }
      break;







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** Close a VDBE cursor and release all the resources that cursor 
** happens to hold.
*/
void sqlite3VdbeFreeCursor(Vdbe *p, VdbeCursor *pCx){
  if( pCx==0 ){
    return;
  }
  assert( pCx->pBtx==0 || pCx->eCurType==CURTYPE_BTREE );
  switch( pCx->eCurType ){
    case CURTYPE_SORTER: {
      sqlite3VdbeSorterClose(p->db, pCx);
      break;
    }
    case CURTYPE_BTREE: {
      if( pCx->pBtx ){
        sqlite3BtreeClose(pCx->pBtx);
        /* The pCx->pCursor will be close automatically, if it exists, by
        ** the call above. */
      }else{
        assert( pCx->uc.pCursor!=0 );
        sqlite3BtreeCloseCursor(pCx->uc.pCursor);
      }
      break;

Changes to src/vdbesort.c.

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  ** to exceed the maximum merge count */
#if SQLITE_MAX_WORKER_THREADS>=SORTER_MAX_MERGE_COUNT
  if( nWorker>=SORTER_MAX_MERGE_COUNT ){
    nWorker = SORTER_MAX_MERGE_COUNT-1;
  }
#endif

  assert( pCsr->pKeyInfo && pCsr->pBt==0 );
  assert( pCsr->eCurType==CURTYPE_SORTER );
  szKeyInfo = sizeof(KeyInfo) + (pCsr->pKeyInfo->nField-1)*sizeof(CollSeq*);
  sz = sizeof(VdbeSorter) + nWorker * sizeof(SortSubtask);

  pSorter = (VdbeSorter*)sqlite3DbMallocZero(db, sz + szKeyInfo);
  pCsr->uc.pSorter = pSorter;
  if( pSorter==0 ){







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  ** to exceed the maximum merge count */
#if SQLITE_MAX_WORKER_THREADS>=SORTER_MAX_MERGE_COUNT
  if( nWorker>=SORTER_MAX_MERGE_COUNT ){
    nWorker = SORTER_MAX_MERGE_COUNT-1;
  }
#endif

  assert( pCsr->pKeyInfo && pCsr->pBtx==0 );
  assert( pCsr->eCurType==CURTYPE_SORTER );
  szKeyInfo = sizeof(KeyInfo) + (pCsr->pKeyInfo->nField-1)*sizeof(CollSeq*);
  sz = sizeof(VdbeSorter) + nWorker * sizeof(SortSubtask);

  pSorter = (VdbeSorter*)sqlite3DbMallocZero(db, sz + szKeyInfo);
  pCsr->uc.pSorter = pSorter;
  if( pSorter==0 ){