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 cced591d02c7c15114a1d1c67ce64b8a988f3bf1..9c88ce661dc4337c7a96e6917d6c3d3a1e8102a6 100644 (file)
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -2664,7 +2664,10 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
 
    if (node->aggstrategy == AGG_HASHED)
    {
-       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;
        /* Compute the columns we actually need to hash on */
        aggstate->hash_needed = find_hash_columns(aggstate);