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: REL_10_16~78
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=1dbe627fd6bf889ad117a706ff474f7382a66465;p=thirdparty%2Fpostgresql.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 1dcd8e19ed2..8f9d588e5a5 100644
--- 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;
 	}