From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Fri, 20 Nov 2020 12:41:14 +0000 (+0200)
Subject: Skip allocating hash table in EXPLAIN-only mode.
X-Git-Tag: REL9_5_25~62
X-Git-Url: http://git.postgresql.org/gitweb/?a=commitdiff_plain;h=ded7db4c1dddcead3184b17619ddc5c203db42fe;p=postgresql.git

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 a9e1fbb842e..41bfbb75d6f 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -2254,7 +2254,10 @@ 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);