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Performance optimization in the memory allocation of allocateCursor.

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FossilOrigin-Name: 9d16323d14370b737399eb52b69b70cc614f78fb8a1e93f21a348c34a30dd456
This commit is contained in:
drh
2021-05-15 19:36:36 +00:00
parent 86c779fe42
commit 2454e4a901
4 changed files with 43 additions and 21 deletions
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40
src/vdbe.c
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@@ -275,18 +275,36 @@ static VdbeCursor *allocateCursor(
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];
sqlite3BtreeCursorZero(pCx->uc.pCursor);
/* There used to be a call to sqlite3VdbeMemClearAndResize() to make sure
** the pMem used to hold space for the cursor has enough storage available
** in pMem->zMalloc. But for the special case of the aMem[] entries used
** to hold cursors, it is faster to in-line the logic. */
assert( pMem->flags==MEM_Undefined );
assert( (pMem->flags & MEM_Dyn)==0 );
assert( pMem->szMalloc==0 || pMem->z==pMem->zMalloc );
if( pMem->szMalloc<nByte ){
if( pMem->szMalloc>0 ){
sqlite3DbFreeNN(pMem->db, pMem->zMalloc);
}
pMem->z = pMem->zMalloc = sqlite3DbMallocRaw(pMem->db, nByte);
if( pMem->zMalloc==0 ){
pMem->szMalloc = 0;
return 0;
}
pMem->szMalloc = nByte;
}
p->apCsr[iCur] = pCx = (VdbeCursor*)pMem->zMalloc;
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];
sqlite3BtreeCursorZero(pCx->uc.pCursor);
}
return pCx;
}