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Factor the saveAllCursors() routine of btree.c into two separate routines,

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for a noticable performance improvement.

FossilOrigin-Name: 3eb084390382c108e9b0ff0b29dede58ebb149bc
This commit is contained in:
drh
2014-08-22 22:26:07 +00:00
parent 75e2a2d362
commit 637f3d83b9
3 changed files with 38 additions and 11 deletions
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35
src/btree.c
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@@ -629,16 +629,42 @@ static int saveCursorPosition(BtCursor *pCur){
return rc;
}
/* Forward reference */
static int SQLITE_NOINLINE saveCursorsOnList(BtCursor*,Pgno,BtCursor*);
/*
** Save the positions of all cursors (except pExcept) that are open on
** the table with root-page iRoot. Usually, this is called just before cursor
** pExcept is used to modify the table (BtreeDelete() or BtreeInsert()).
** the table with root-page iRoot. "Saving the cursor position" means that
** the location in the btree is remembered in such a way that it can be
** moved back to the same spot after the btree has been modified. This
** routine is called just before cursor pExcept is used to modify the
** table, for example in BtreeDelete() or BtreeInsert().
**
** 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.
*/
static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
BtCursor *p;
assert( sqlite3_mutex_held(pBt->mutex) );
assert( pExcept==0 || pExcept->pBt==pBt );
BtCursor *p;
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;
}
/* This helper routine to saveAllCursors does the actual work of saving
** the cursors if and when a cursor is found that actually requires saving.
** The common case is that no cursors need to be saved, so this routine is
** broken out from its caller to avoid unnecessary stack pointer movement.
*/
static int SQLITE_NOINLINE saveCursorsOnList(
BtCursor *p, /* The first cursor that needs saving */
Pgno iRoot, /* Only save cursor with this iRoot. Save all if zero */
BtCursor *pExcept /* Do not save this cursor */
){
do{
if( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) ){
if( p->eState==CURSOR_VALID ){
int rc = saveCursorPosition(p);
@@ -650,7 +676,8 @@ static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
btreeReleaseAllCursorPages(p);
}
}
}
p = p->pNext;
}while( p );
return SQLITE_OK;
}