/*
* btrestrpos() -- restore scan to last saved position
*/
void
btrestrpos(IndexScanDesc scan)
{
BTScanOpaque so = (BTScanOpaque) scan->opaque;
/* Restore the marked positions of any array keys */
if (so->numArrayKeys)
_bt_restore_array_keys(scan);
if (so->markItemIndex >= 0)
{
/*
* The scan has never moved to a new page since the last mark. Just
* restore the itemIndex.
*
* NB: In this case we can't count on anything in so->markPos to be
* accurate.
*/
so->currPos.itemIndex = so->markItemIndex;
}
else
{
/*
* The scan moved to a new page after last mark or restore, and we are
* now restoring to the marked page. We aren't holding any read
* locks, but if we're still holding the pin for the current position,
* we must drop it.
*/
if (BTScanPosIsValid(so->currPos))
{
/* Before leaving current page, deal with any killed items */
if (so->numKilled > 0)
_bt_killitems(scan);
BTScanPosUnpinIfPinned(so->currPos);
}
if (BTScanPosIsValid(so->markPos))
{
/* bump pin on mark buffer for assignment to current buffer */
if (BTScanPosIsPinned(so->markPos))
IncrBufferRefCount(so->markPos.buf);
memcpy(&so->currPos, &so->markPos,
offsetof(BTScanPosData, items[1]) +
so->markPos.lastItem * sizeof(BTScanPosItem));
if (so->currTuples)
memcpy(so->currTuples, so->markTuples,
so->markPos.nextTupleOffset);
}
else
BTScanPosInvalidate(so->currPos);
}
}
/*
* btrestrpos() -- restore scan to last saved position
*/
Datum
btrestrpos(PG_FUNCTION_ARGS)
{
IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
BTScanOpaque so = (BTScanOpaque) scan->opaque;
/* Restore the marked positions of any array keys */
if (so->numArrayKeys)
_bt_restore_array_keys(scan);
if (so->markItemIndex >= 0)
{
/*
* The scan has never moved to a new___ page since the last mark. Just
* restore the itemIndex.
*
* NB: In this case we can't count on anything in so->markPos to be
* accurate.
*/
so->currPos.itemIndex = so->markItemIndex;
}
else if (so->currPos.currPage == so->markPos.currPage)
{
/*
* so->markItemIndex < 0 but mark and current positions are on the
* same page. This would be an unusual case, where the scan moved to
* a new___ index page after the mark, restored, and later restored again
* without moving off the marked page. It is not clear that this code
* can currently be reached, but it seems better to make this function
* robust for this case than to Assert() or elog() that it can't
* happen.
*
* We neither want to set so->markItemIndex >= 0 (because that could
* cause a later move to a new___ page to redo the memcpy() executions)
* nor re-execute the memcpy() functions for a restore within the same
* page. The previous restore to this page already set everything
* except markPos as it should be.
*/
so->currPos.itemIndex = so->markPos.itemIndex;
}
else
{
/*
* The scan moved to a new___ page after last mark or restore, and we are
* now restoring to the marked page. We aren't holding any read
* locks, but if we're still holding the pin for the current position,
* we must drop it.
*/
if (BTScanPosIsValid(so->currPos))
{
/* Before leaving current page, deal with any killed items */
if (so->numKilled > 0)
_bt_killitems(scan);
BTScanPosUnpinIfPinned(so->currPos);
}
if (BTScanPosIsValid(so->markPos))
{
/* bump pin on mark buffer for assignment to current buffer */
if (BTScanPosIsPinned(so->markPos))
IncrBufferRefCount(so->markPos.buf);
memcpy(&so->currPos, &so->markPos,
offsetof(BTScanPosData, items[1]) +
so->markPos.lastItem * sizeof(BTScanPosItem));
if (so->currTuples)
memcpy(so->currTuples, so->markTuples,
so->markPos.nextTupleOffset);
}
else
BTScanPosInvalidate(so->currPos);
}
PG_RETURN_VOID();
}
