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Another performance tweak: Split the sqlite3BtreeCursorHasMoved() routine

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into two with the second routine named sqlite3BtreeCursorRestore().  The first
now only reports whether or not the cursor has moved and the second tries to
restore the cursor.  This allows the sqlite3VdbeCursorMoveto() routine to be
refactored to avoid stack pointer movements, for a noticable performance gain.

FossilOrigin-Name: ce123b5c592556a8cd38b01fcc91ba76231d3098
This commit is contained in:
drh
2014-08-22 23:33:03 +00:00
parent 637f3d83b9
commit 6848dad894
5 changed files with 88 additions and 53 deletions
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51
src/btree.c
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@@ -762,37 +762,48 @@ static int btreeRestoreCursorPosition(BtCursor *pCur){
SQLITE_OK)
/*
** Determine whether or not a cursor has moved from the position it
** was last placed at. Cursors can move when the row they are pointing
** at is deleted out from under them.
** Determine whether or not a cursor has moved from the position where
** it was last placed, or has been invalidated for any other reason.
** Cursors can move when the row they are pointing at is deleted out
** from under them, for example. Cursor might also move if a btree
** is rebalanced.
**
** This routine returns an error code if something goes wrong. The
** integer *pHasMoved is set as follows:
** Calling this routine with a NULL cursor pointer returns false.
**
** 0: The cursor is unchanged
** 1: The cursor is still pointing at the same row, but the pointers
** returned by sqlite3BtreeKeyFetch() or sqlite3BtreeDataFetch()
** might now be invalid because of a balance() or other change to the
** b-tree.
** 2: The cursor is no longer pointing to the row. The row might have
** been deleted out from under the cursor.
** Use the separate sqlite3BtreeCursorRestore() routine to restore a cursor
** back to where it ought to be if this routine returns true.
*/
int sqlite3BtreeCursorHasMoved(BtCursor *pCur, int *pHasMoved){
int sqlite3BtreeCursorHasMoved(BtCursor *pCur){
return pCur && pCur->eState!=CURSOR_VALID;
}
/*
** This routine restores a cursor back to its original position after it
** has been moved by some outside activity (such as a btree rebalance or
** a row having been deleted out from under the cursor).
**
** On success, the *pDifferentRow parameter is false if the cursor is left
** pointing at exactly the same row. *pDifferntRow is the row the cursor
** was pointing to has been deleted, forcing the cursor to point to some
** nearby row.
**
** This routine should only be called for a cursor that just returned
** TRUE from sqlite3BtreeCursorHasMoved().
*/
int sqlite3BtreeCursorRestore(BtCursor *pCur, int *pDifferentRow){
int rc;
if( pCur->eState==CURSOR_VALID ){
*pHasMoved = 0;
return SQLITE_OK;
}
assert( pCur!=0 );
assert( pCur->eState!=CURSOR_VALID );
rc = restoreCursorPosition(pCur);
if( rc ){
*pHasMoved = 2;
*pDifferentRow = 1;
return rc;
}
if( pCur->eState!=CURSOR_VALID || NEVER(pCur->skipNext!=0) ){
*pHasMoved = 2;
*pDifferentRow = 1;
}else{
*pHasMoved = 1;
*pDifferentRow = 0;
}
return SQLITE_OK;
}