diff options
Diffstat (limited to 'src/backend/executor/nodeWorktablescan.c')
| -rw-r--r-- | src/backend/executor/nodeWorktablescan.c | 19 |
1 files changed, 12 insertions, 7 deletions
diff --git a/src/backend/executor/nodeWorktablescan.c b/src/backend/executor/nodeWorktablescan.c index 49b7279aba8..47f6e202ec1 100644 --- a/src/backend/executor/nodeWorktablescan.c +++ b/src/backend/executor/nodeWorktablescan.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/executor/nodeWorktablescan.c,v 1.3 2008/10/23 15:29:23 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/executor/nodeWorktablescan.c,v 1.4 2008/10/28 17:13:51 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -31,14 +31,21 @@ WorkTableScanNext(WorkTableScanState *node) { TupleTableSlot *slot; EState *estate; - ScanDirection direction; Tuplestorestate *tuplestorestate; /* * get information from the estate and scan state + * + * Note: we intentionally do not support backward scan. Although it would + * take only a couple more lines here, it would force nodeRecursiveunion.c + * to create the tuplestore with backward scan enabled, which has a + * performance cost. In practice backward scan is never useful for a + * worktable plan node, since it cannot appear high enough in the plan + * tree of a scrollable cursor to be exposed to a backward-scan + * requirement. So it's not worth expending effort to support it. */ estate = node->ss.ps.state; - direction = estate->es_direction; + Assert(ScanDirectionIsForward(estate->es_direction)); tuplestorestate = node->rustate->working_table; @@ -46,9 +53,7 @@ WorkTableScanNext(WorkTableScanState *node) * Get the next tuple from tuplestore. Return NULL if no more tuples. */ slot = node->ss.ss_ScanTupleSlot; - (void) tuplestore_gettupleslot(tuplestorestate, - ScanDirectionIsForward(direction), - slot); + (void) tuplestore_gettupleslot(tuplestorestate, true, slot); return slot; } @@ -114,7 +119,7 @@ ExecInitWorkTableScan(WorkTableScan *node, EState *estate, int eflags) WorkTableScanState *scanstate; /* check for unsupported flags */ - Assert(!(eflags & EXEC_FLAG_MARK)); + Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK))); /* * WorkTableScan should not have any children. |