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 75e5bbf209d536613eaaa8411b073346f3dac1fd..8a0bd887bf003792a53ce4b5b4f9f799a35e7fad 100644 (file)
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -3665,7 +3665,11 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
                            &aggstate->hash_ngroups_limit,
                            &aggstate->hash_planned_partitions);
        find_hash_columns(aggstate);
-       build_hash_tables(aggstate);
+
+       /* Skip massive memory allocation if we are just doing EXPLAIN */
+       if (!(eflags & EXEC_FLAG_EXPLAIN_ONLY))
+           build_hash_tables(aggstate);
+
        aggstate->table_filled = false;
 
        /* Initialize this to 1, meaning nothing spilled, yet */