diff options
Diffstat (limited to 'src/backend/optimizer')
| -rw-r--r-- | src/backend/optimizer/path/allpaths.c | 13 | ||||
| -rw-r--r-- | src/backend/optimizer/plan/planner.c | 3 |
2 files changed, 14 insertions, 2 deletions
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index 5db1688bf04..5f74d3b36d9 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -620,7 +620,20 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel, * the SubqueryScanPath as not parallel-safe. (Note that * set_subquery_pathlist() might push some of these quals down * into the subquery itself, but that doesn't change anything.) + * + * We can't push sub-select containing LIMIT/OFFSET to workers as + * there is no guarantee that the row order will be fully + * deterministic, and applying LIMIT/OFFSET will lead to + * inconsistent results at the top-level. (In some cases, where + * the result is ordered, we could relax this restriction. But it + * doesn't currently seem worth expending extra effort to do so.) */ + { + Query *subquery = castNode(Query, rte->subquery); + + if (limit_needed(subquery)) + return; + } break; case RTE_JOIN: diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c index 96bf0601a8e..e589471fee8 100644 --- a/src/backend/optimizer/plan/planner.c +++ b/src/backend/optimizer/plan/planner.c @@ -123,7 +123,6 @@ static void preprocess_rowmarks(PlannerInfo *root); static double preprocess_limit(PlannerInfo *root, double tuple_fraction, int64 *offset_est, int64 *count_est); -static bool limit_needed(Query *parse); static void remove_useless_groupby_columns(PlannerInfo *root); static List *preprocess_groupclause(PlannerInfo *root, List *force); static List *extract_rollup_sets(List *groupingSets); @@ -2870,7 +2869,7 @@ preprocess_limit(PlannerInfo *root, double tuple_fraction, * a key distinction: here we need hard constants in OFFSET/LIMIT, whereas * in preprocess_limit it's good enough to consider estimated values. */ -static bool +bool limit_needed(Query *parse) { Node *node; |