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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

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Overview
Comment:Performance improvement by avoiding unnecessary calls to memset().
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: 85940468e6f93f7c493fbc129f13cf6233c5d0c0
User & Date: drh 2009-11-18 23:01:26
Context
2009-11-19
14:52
Merge the fts3-refactor branch with the trunk. check-in: c8d2bd37 user: dan tags: fts3-refactor
14:48
Fix a bug introduced with recent optimizations: The unary minus operator is TK_UMINUS, not TK_MINUS. check-in: 4bd43307 user: drh tags: trunk
2009-11-18
23:01
Performance improvement by avoiding unnecessary calls to memset(). check-in: 85940468 user: drh tags: trunk
01:25
Suppress more instances of unnecessary OP_IsNull and OP_Affinity opcodes. check-in: bf6c0bd1 user: drh tags: trunk
Changes
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Changes to src/btree.c.

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**
** 4:  There must be an active transaction.
**
** No checking is done to make sure that page iTable really is the
** root page of a b-tree.  If it is not, then the cursor acquired
** will not work correctly.
**
** It is assumed that the sqlite3BtreeCursorSize() bytes of memory 
** pointed to by pCur have been zeroed by the caller.
*/
static int btreeCursor(
  Btree *p,                              /* The btree */
  int iTable,                            /* Root page of table to open */
  int wrFlag,                            /* 1 to write. 0 read-only */
  struct KeyInfo *pKeyInfo,              /* First arg to comparison function */
  BtCursor *pCur                         /* Space for new cursor */
................................................................................
** sufficient storage to hold a cursor.  The BtCursor object is opaque
** to users so they cannot do the sizeof() themselves - they must call
** this routine.
*/
int sqlite3BtreeCursorSize(void){
  return ROUND8(sizeof(BtCursor));
}













/*
** Set the cached rowid value of every cursor in the same database file
** as pCur and having the same root page number as pCur.  The value is
** set to iRowid.
**
** Only positive rowid values are considered valid for this cache.







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**
** 4:  There must be an active transaction.
**
** No checking is done to make sure that page iTable really is the
** root page of a b-tree.  If it is not, then the cursor acquired
** will not work correctly.
**
** It is assumed that the sqlite3BtreeCursorZero() has been called
** on pCur to initialize the memory space prior to invoking this routine.
*/
static int btreeCursor(
  Btree *p,                              /* The btree */
  int iTable,                            /* Root page of table to open */
  int wrFlag,                            /* 1 to write. 0 read-only */
  struct KeyInfo *pKeyInfo,              /* First arg to comparison function */
  BtCursor *pCur                         /* Space for new cursor */
................................................................................
** sufficient storage to hold a cursor.  The BtCursor object is opaque
** to users so they cannot do the sizeof() themselves - they must call
** this routine.
*/
int sqlite3BtreeCursorSize(void){
  return ROUND8(sizeof(BtCursor));
}

/*
** Initialize memory that will be converted into a BtCursor object.
**
** The simple approach here would be to memset() the entire object
** to zero.  But it turns out that the apPage[] and aiIdx[] arrays
** do not need to be zeroed and they are large, so we can save a lot
** of run-time by skipping the initialization of those elements.
*/
void sqlite3BtreeCursorZero(BtCursor *p){
  memset(p, 0, offsetof(BtCursor, iPage));
}

/*
** Set the cached rowid value of every cursor in the same database file
** as pCur and having the same root page number as pCur.  The value is
** set to iRowid.
**
** Only positive rowid values are considered valid for this cache.

Changes to src/btree.h.

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  Btree*,                              /* BTree containing table to open */
  int iTable,                          /* Index of root page */
  int wrFlag,                          /* 1 for writing.  0 for read-only */
  struct KeyInfo*,                     /* First argument to compare function */
  BtCursor *pCursor                    /* Space to write cursor structure */
);
int sqlite3BtreeCursorSize(void);


int sqlite3BtreeCloseCursor(BtCursor*);
int sqlite3BtreeMovetoUnpacked(
  BtCursor*,
  UnpackedRecord *pUnKey,
  i64 intKey,
  int bias,







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  Btree*,                              /* BTree containing table to open */
  int iTable,                          /* Index of root page */
  int wrFlag,                          /* 1 for writing.  0 for read-only */
  struct KeyInfo*,                     /* First argument to compare function */
  BtCursor *pCursor                    /* Space to write cursor structure */
);
int sqlite3BtreeCursorSize(void);
void sqlite3BtreeCursorZero(BtCursor*);

int sqlite3BtreeCloseCursor(BtCursor*);
int sqlite3BtreeMovetoUnpacked(
  BtCursor*,
  UnpackedRecord *pUnKey,
  i64 intKey,
  int bias,

Changes to src/vdbe.c.

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  assert( iCur<p->nCursor );
  if( p->apCsr[iCur] ){
    sqlite3VdbeFreeCursor(p, p->apCsr[iCur]);
    p->apCsr[iCur] = 0;
  }
  if( SQLITE_OK==sqlite3VdbeMemGrow(pMem, nByte, 0) ){
    p->apCsr[iCur] = pCx = (VdbeCursor*)pMem->z;
    memset(pCx, 0, nByte);
    pCx->iDb = iDb;
    pCx->nField = nField;
    if( nField ){
      pCx->aType = (u32 *)&pMem->z[ROUND8(sizeof(VdbeCursor))];
    }
    if( isBtreeCursor ){
      pCx->pCursor = (BtCursor*)
          &pMem->z[ROUND8(sizeof(VdbeCursor))+2*nField*sizeof(u32)];

    }
  }
  return pCx;
}

/*
** Try to convert a value into a numeric representation if we can







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  assert( iCur<p->nCursor );
  if( p->apCsr[iCur] ){
    sqlite3VdbeFreeCursor(p, p->apCsr[iCur]);
    p->apCsr[iCur] = 0;
  }
  if( SQLITE_OK==sqlite3VdbeMemGrow(pMem, nByte, 0) ){
    p->apCsr[iCur] = pCx = (VdbeCursor*)pMem->z;
    memset(pCx, 0, sizeof(VdbeCursor));
    pCx->iDb = iDb;
    pCx->nField = nField;
    if( nField ){
      pCx->aType = (u32 *)&pMem->z[ROUND8(sizeof(VdbeCursor))];
    }
    if( isBtreeCursor ){
      pCx->pCursor = (BtCursor*)
          &pMem->z[ROUND8(sizeof(VdbeCursor))+2*nField*sizeof(u32)];
      sqlite3BtreeCursorZero(pCx->pCursor);
    }
  }
  return pCx;
}

/*
** Try to convert a value into a numeric representation if we can