v6-0003-use-shared-buffers-when-failsafe-active.patch

From 52c802a00572b382ee0203b0038dbe509e4ecb72 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Wed, 22 Feb 2023 12:26:01 -0500
Subject: [PATCH v6 3/6] use shared buffers when failsafe active

---
 doc/src/sgml/config.sgml             | 8 +++++---
 src/backend/access/heap/vacuumlazy.c | 7 +++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e5c41cc6c6..fca38a4514 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -9291,9 +9291,11 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         the failsafe to trigger during any <command>VACUUM</command>.
        </para>
        <para>
-        When the failsafe is triggered, any cost-based delay that is
-        in effect will no longer be applied, and further non-essential
-        maintenance tasks (such as index vacuuming) are bypassed.
+        When the failsafe is triggered, any cost-based delay that is in effect
+        will no longer be applied, further non-essential maintenance tasks
+        (such as index vacuuming) are bypassed, and any Buffer Access Strategy
+        in use will be abandoned and the vacuum will be free to use as many
+        shared buffers as it needs to finish vacuuming the table.
        </para>
        <para>
         The default is 1.6 billion transactions.  Although users can
diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 8f14cf85f3..3de7976cf6 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -2622,6 +2622,13 @@ lazy_check_wraparound_failsafe(LVRelState *vacrel)
 	if (unlikely(vacuum_xid_failsafe_check(&vacrel->cutoffs)))
 	{
 		vacrel->failsafe_active = true;
+		/*
+		 * Abandon use of a buffer access strategy when entering failsafe mode,
+		 * as completing the ongoing VACUUM is our top priority.
+		 * Assume the caller who allocated the memory for the
+		 * BufferAccessStrategy object will free it.
+		 */
+		vacrel->bstrategy = NULL;
 
 		/* Disable index vacuuming, index cleanup, and heap rel truncation */
 		vacrel->do_index_vacuuming = false;
-- 
2.37.2