diff options
| -rw-r--r-- | src/backend/optimizer/path/costsize.c | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index 1c20edcdfeb..2a49639f125 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -3114,11 +3114,21 @@ cost_rescan(PlannerInfo *root, Path *path, case T_HashJoin: /* - * Assume that all of the startup cost represents hash table - * building, which we won't have to do over. + * If it's a single-batch join, we don't need to rebuild the hash + * table during a rescan. */ - *rescan_startup_cost = 0; - *rescan_total_cost = path->total_cost - path->startup_cost; + if (((HashPath *) path)->num_batches == 1) + { + /* Startup cost is exactly the cost of hash table building */ + *rescan_startup_cost = 0; + *rescan_total_cost = path->total_cost - path->startup_cost; + } + else + { + /* Otherwise, no special treatment */ + *rescan_startup_cost = path->startup_cost; + *rescan_total_cost = path->total_cost; + } break; case T_CteScan: case T_WorkTableScan: |