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Performance optimization in the B-Tree cursor allocator btreeCursor(), making

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it about 800K CPU cycles faster in speedtest1, and reducing the executable
size by about 100 bytes.

FossilOrigin-Name: 9df939716ace8cfe60340bbe83fc52d452ea40c29c856c588f9a1b8973282391
This commit is contained in:
drh
2021-12-03 13:42:41 +00:00
parent 65a3c8508d
commit 2f0bc1d41b
3 changed files with 50 additions and 38 deletions
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74
src/btree.c
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@@ -2693,30 +2693,40 @@ static int removeFromSharingList(BtShared *pBt){
** MX_CELL_SIZE(pBt) bytes with a 4-byte prefix for a left-child
** pointer.
*/
static void allocateTempSpace(BtShared *pBt){
if( !pBt->pTmpSpace ){
pBt->pTmpSpace = sqlite3PageMalloc( pBt->pageSize );
/* One of the uses of pBt->pTmpSpace is to format cells before
** inserting them into a leaf page (function fillInCell()). If
** a cell is less than 4 bytes in size, it is rounded up to 4 bytes
** by the various routines that manipulate binary cells. Which
** can mean that fillInCell() only initializes the first 2 or 3
** bytes of pTmpSpace, but that the first 4 bytes are copied from
** it into a database page. This is not actually a problem, but it
** does cause a valgrind error when the 1 or 2 bytes of unitialized
** data is passed to system call write(). So to avoid this error,
** zero the first 4 bytes of temp space here.
**
** Also: Provide four bytes of initialized space before the
** beginning of pTmpSpace as an area available to prepend the
** left-child pointer to the beginning of a cell.
*/
if( pBt->pTmpSpace ){
memset(pBt->pTmpSpace, 0, 8);
pBt->pTmpSpace += 4;
}
static SQLITE_NOINLINE int allocateTempSpace(BtShared *pBt){
assert( pBt!=0 );
assert( pBt->pTmpSpace==0 );
/* This routine is called only by btreeCursor() when allocating the
** first write cursor for the BtShared object */
assert( pBt->pCursor!=0 && (pBt->pCursor->curFlags & BTCF_WriteFlag)!=0 );
pBt->pTmpSpace = sqlite3PageMalloc( pBt->pageSize );
if( pBt->pTmpSpace==0 ){
BtCursor *pCur = pBt->pCursor;
pBt->pCursor = pCur->pNext; /* Unlink the cursor */
memset(pCur, 0, sizeof(*pCur));
return SQLITE_NOMEM_BKPT;
}
/* One of the uses of pBt->pTmpSpace is to format cells before
** inserting them into a leaf page (function fillInCell()). If
** a cell is less than 4 bytes in size, it is rounded up to 4 bytes
** by the various routines that manipulate binary cells. Which
** can mean that fillInCell() only initializes the first 2 or 3
** bytes of pTmpSpace, but that the first 4 bytes are copied from
** it into a database page. This is not actually a problem, but it
** does cause a valgrind error when the 1 or 2 bytes of unitialized
** data is passed to system call write(). So to avoid this error,
** zero the first 4 bytes of temp space here.
**
** Also: Provide four bytes of initialized space before the
** beginning of pTmpSpace as an area available to prepend the
** left-child pointer to the beginning of a cell.
*/
if( pBt->pTmpSpace ){
memset(pBt->pTmpSpace, 0, 8);
pBt->pTmpSpace += 4;
}
return SQLITE_OK;
}
/*
@@ -4457,10 +4467,6 @@ static int btreeCursor(
assert( pBt->pPage1 && pBt->pPage1->aData );
assert( wrFlag==0 || (pBt->btsFlags & BTS_READ_ONLY)==0 );
if( wrFlag ){
allocateTempSpace(pBt);
if( pBt->pTmpSpace==0 ) return SQLITE_NOMEM_BKPT;
}
if( iTable<=1 ){
if( iTable<1 ){
return SQLITE_CORRUPT_BKPT;
@@ -4477,19 +4483,25 @@ static int btreeCursor(
pCur->pKeyInfo = pKeyInfo;
pCur->pBtree = p;
pCur->pBt = pBt;
pCur->curFlags = wrFlag ? BTCF_WriteFlag : 0;
pCur->curPagerFlags = wrFlag ? 0 : PAGER_GET_READONLY;
pCur->curFlags = 0;
/* If there are two or more cursors on the same btree, then all such
** cursors *must* have the BTCF_Multiple flag set. */
for(pX=pBt->pCursor; pX; pX=pX->pNext){
if( pX->pgnoRoot==iTable ){
pX->curFlags |= BTCF_Multiple;
pCur->curFlags |= BTCF_Multiple;
pCur->curFlags = BTCF_Multiple;
}
}
pCur->eState = CURSOR_INVALID;
pCur->pNext = pBt->pCursor;
pBt->pCursor = pCur;
pCur->eState = CURSOR_INVALID;
if( wrFlag ){
pCur->curFlags |= BTCF_WriteFlag;
pCur->curPagerFlags = 0;
if( pBt->pTmpSpace==0 ) return allocateTempSpace(pBt);
}else{
pCur->curPagerFlags = PAGER_GET_READONLY;
}
return SQLITE_OK;
}
static int btreeCursorWithLock(