Skip allocating hash table in EXPLAIN-only mode.

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 d87677d659983451c718cb4a24b5e5cf33e0c19f..5bf9e99bbc86b776ac2488518d3d8626b0fb4e31 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 */