Skip allocating hash table in EXPLAIN-only mode.

This is a backpatch of commit 2cccb627f1, backpatched due to popular
demand. Backpatch to all supported versions.

Author: Alexey Bashtanov
Discussion: https://www.postgresql.org/message-id/36823f65-050d-ae24-aa4d-a37726998240%40imap.cc

diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index 1dcd8e19ed2351ca1193c3d39a520658eec68cc3..8f9d588e5a5c1a50fcd23efbf0f823828fd49c6c 100644 (file)
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -3073,7 +3073,11 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
                aggstate->hash_pergroup = palloc0(sizeof(AggStatePerGroup) * numHashes);
 
                find_hash_columns(aggstate);
-               build_hash_table(aggstate);
+
+               /* Skip massive memory allocation if we are just doing EXPLAIN */
+               if (!(eflags & EXEC_FLAG_EXPLAIN_ONLY))
+                       build_hash_table(aggstate);
+
                aggstate->table_filled = false;
        }