From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Fri, 13 Nov 2020 13:39:31 -0300
Subject: [PATCH] Avoid errors in brin summarization..

..which can happen if an index is reindexed concurrently
---
 src/backend/access/brin/brin.c | 34 ++++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 1f72562c60..a1089d5f9e 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -886,9 +886,9 @@ brin_summarize_range(PG_FUNCTION_ARGS)
 
 	/*
 	 * We must lock table before index to avoid deadlocks.  However, if the
-	 * passed indexoid isn't an index then IndexGetRelation() will fail.
-	 * Rather than emitting a not-very-helpful error message, postpone
-	 * complaining, expecting that the is-it-an-index test below will fail.
+	 * passed indexoid isn't an index, then IndexGetRelation(true) would
+	 * emit a not-very-helpful error message.  Instead, postpone complaining
+	 * until the is-it-an-index test, below.
 	 */
 	heapoid = IndexGetRelation(indexoid, true);
 	if (OidIsValid(heapoid))
@@ -896,11 +896,33 @@ brin_summarize_range(PG_FUNCTION_ARGS)
 	else
 		heapRel = NULL;
 
-	indexRel = index_open(indexoid, ShareUpdateExclusiveLock);
+	indexRel = try_relation_open(indexoid, ShareUpdateExclusiveLock);
+
+	/* Silently skip autovacuum work-items if an index has disappeared. */
+	if (!indexRel)
+	{
+		if (heapRel)
+			table_close(heapRel, ShareUpdateExclusiveLock);
+
+		PG_RETURN_INT32(0);
+	}
+
+	/* If passed a non-index, fail noisily */
+	if (indexRel->rd_rel->relkind != RELKIND_INDEX)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("\"%s\" is not an index",
+						RelationGetRelationName(indexRel))));
+
+	/* If the table wasn't opened for some other reason, silently skip it */
+	if (!heapRel)
+	{
+		relation_close(indexRel, ShareUpdateExclusiveLock);
+		PG_RETURN_INT32(0);
+	}
 
 	/* Must be a BRIN index */
-	if (indexRel->rd_rel->relkind != RELKIND_INDEX ||
-		indexRel->rd_rel->relam != BRIN_AM_OID)
+	if (indexRel->rd_rel->relam != BRIN_AM_OID)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a BRIN index",
-- 
2.17.0


--HuscSE0D68UGttcd--