From e9d9ba2a4ddc39e331dd8461b511aa59ec0dc8af Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 1 Nov 2021 16:24:39 -0400 Subject: Avoid some other O(N^2) hazards in list manipulation. In the same spirit as 6301c3ada, fix some more places where we were using list_delete_first() in a loop and thereby risking O(N^2) behavior. It's not clear that the lists manipulated in these spots can get long enough to be really problematic ... but it's not clear that they can't, either, and the fixes are simple enough. As before, back-patch to v13. Discussion: https://postgr.es/m/CD2F0E7F-9822-45EC-A411-AE56F14DEA9F@amazon.com --- src/backend/executor/nodeAgg.c | 17 +++++------------ 1 file changed, 5 insertions(+), 12 deletions(-) (limited to 'src/backend/executor') diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c index c99a0de4ddb..f5a187cae3a 100644 --- a/src/backend/executor/nodeAgg.c +++ b/src/backend/executor/nodeAgg.c @@ -2584,8 +2584,9 @@ agg_refill_hash_table(AggState *aggstate) if (aggstate->hash_batches == NIL) return false; - batch = linitial(aggstate->hash_batches); - aggstate->hash_batches = list_delete_first(aggstate->hash_batches); + /* hash_batches is a stack, with the top item at the end of the list */ + batch = llast(aggstate->hash_batches); + aggstate->hash_batches = list_delete_last(aggstate->hash_batches); hash_agg_set_limits(aggstate->hashentrysize, batch->input_card, batch->used_bits, &aggstate->hash_mem_limit, @@ -3098,7 +3099,7 @@ hashagg_spill_finish(AggState *aggstate, HashAggSpill *spill, int setno) new_batch = hashagg_batch_new(tape, setno, spill->ntuples[i], cardinality, used_bits); - aggstate->hash_batches = lcons(new_batch, aggstate->hash_batches); + aggstate->hash_batches = lappend(aggstate->hash_batches, new_batch); aggstate->hash_batches_used++; } @@ -3113,8 +3114,6 @@ hashagg_spill_finish(AggState *aggstate, HashAggSpill *spill, int setno) static void hashagg_reset_spill_state(AggState *aggstate) { - ListCell *lc; - /* free spills from initial pass */ if (aggstate->hash_spills != NULL) { @@ -3132,13 +3131,7 @@ hashagg_reset_spill_state(AggState *aggstate) } /* free batches */ - foreach(lc, aggstate->hash_batches) - { - HashAggBatch *batch = (HashAggBatch *) lfirst(lc); - - pfree(batch); - } - list_free(aggstate->hash_batches); + list_free_deep(aggstate->hash_batches); aggstate->hash_batches = NIL; /* close tape set */ -- cgit v1.2.3