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Put BtCursor objects on a singly-linked list instead of a doubly-linked list.

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Add the BTCF_Multiple flag.  Only invoke saveAllCursors() when using a cursor
that has BTCF_Multiple set.

FossilOrigin-Name: 429ccef2b36fc46e92914eb54afd5f800b1a40ff
This commit is contained in:
drh
2015-06-30 02:47:36 +00:00
parent 98ef0f6c48
commit 27fb746cde
4 changed files with 51 additions and 23 deletions
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54
src/btree.c
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@@ -655,6 +655,15 @@ static int SQLITE_NOINLINE saveCursorsOnList(BtCursor*,Pgno,BtCursor*);
** routine is called just before cursor pExcept is used to modify the
** table, for example in BtreeDelete() or BtreeInsert().
**
** If there are two or more cursors on the same btree, then all such
** cursors should have their BTCF_Multiple flag set. The btreeCursor()
** routine enforces that rule. This routine only needs to be called in
** the uncommon case when pExpect has the BTCF_Multiple flag set.
**
** If pExpect!=NULL and if no other cursors are found on the same root-page,
** then the BTCF_Multiple flag on pExpect is cleared, to avoid another
** pointless call to this routine.
**
** Implementation note: This routine merely checks to see if any cursors
** need to be saved. It calls out to saveCursorsOnList() in the (unusual)
** event that cursors are in need to being saved.
@@ -666,7 +675,9 @@ static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
for(p=pBt->pCursor; p; p=p->pNext){
if( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) ) break;
}
return p ? saveCursorsOnList(p, iRoot, pExcept) : SQLITE_OK;
if( p ) return saveCursorsOnList(p, iRoot, pExcept);
if( pExcept ) pExcept->curFlags &= ~BTCF_Multiple;
return SQLITE_OK;
}
/* This helper routine to saveAllCursors does the actual work of saving
@@ -4015,6 +4026,7 @@ static int btreeCursor(
BtCursor *pCur /* Space for new cursor */
){
BtShared *pBt = p->pBt; /* Shared b-tree handle */
BtCursor *pX; /* Looping over other all cursors */
assert( sqlite3BtreeHoldsMutex(p) );
assert( wrFlag==0 || wrFlag==1 );
@@ -4051,10 +4063,15 @@ static int btreeCursor(
assert( wrFlag==0 || wrFlag==BTCF_WriteFlag );
pCur->curFlags = wrFlag;
pCur->curPagerFlags = wrFlag ? 0 : PAGER_GET_READONLY;
pCur->pNext = pBt->pCursor;
if( pCur->pNext ){
pCur->pNext->pPrev = pCur;
/* 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==(Pgno)iTable ){
pX->curFlags |= BTCF_Multiple;
pCur->curFlags |= BTCF_Multiple;
}
}
pCur->pNext = pBt->pCursor;
pBt->pCursor = pCur;
pCur->eState = CURSOR_INVALID;
return SQLITE_OK;
@@ -4112,13 +4129,18 @@ int sqlite3BtreeCloseCursor(BtCursor *pCur){
BtShared *pBt = pCur->pBt;
sqlite3BtreeEnter(pBtree);
sqlite3BtreeClearCursor(pCur);
if( pCur->pPrev ){
pCur->pPrev->pNext = pCur->pNext;
}else{
assert( pBt->pCursor!=0 );
if( pBt->pCursor==pCur ){
pBt->pCursor = pCur->pNext;
}
if( pCur->pNext ){
pCur->pNext->pPrev = pCur->pPrev;
}else{
BtCursor *pPrev = pBt->pCursor;
do{
if( pPrev->pNext==pCur ){
pPrev->pNext = pCur->pNext;
break;
}
pPrev = pPrev->pNext;
}while( ALWAYS(pPrev) );
}
for(i=0; i<=pCur->iPage; i++){
releasePage(pCur->apPage[i]);
@@ -7895,8 +7917,10 @@ int sqlite3BtreeInsert(
** doing any work. To avoid thwarting these optimizations, it is important
** not to clear the cursor here.
*/
rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur);
if( rc ) return rc;
if( pCur->curFlags & BTCF_Multiple ){
rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur);
if( rc ) return rc;
}
if( pCur->pKeyInfo==0 ){
assert( pKey==0 );
@@ -8042,8 +8066,10 @@ int sqlite3BtreeDelete(BtCursor *pCur){
** deleted writable. Then free any overflow pages associated with the
** entry and finally remove the cell itself from within the page.
*/
rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur);
if( rc ) return rc;
if( pCur->curFlags & BTCF_Multiple ){
rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur);
if( rc ) return rc;
}
/* If this is a delete operation to remove a row from a table b-tree,
** invalidate any incrblob cursors open on the row being deleted. */