Re: BUG #17103: WAL segments are not removed after exceeding max_slot_wal_keep_size

(Somehow the previous mail was broken in many ways. I re-send it.)

At Thu, 29 Jul 2021 16:20:38 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> So it seems to me we need to explicitly prevent unexpected checkpoints
> from happening maybe by enlarging max_wal_size temporily.
> 
> I'll going that way.

I ended up with the attached. It causes a checkpoint reliably exactly
at the aimed timing without.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
From 5c6fa9cd8a6449931de339c628a3a81367f7b22a Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Date: Thu, 29 Jul 2021 16:36:32 +0900
Subject: [PATCH] Make slot test more stable

The slot test is still instable in the case where the test script runs
at relatively slower speed than checkpointing.  Remove the instability
by causing a checkpoint exactly at the aimed timing.
---
 src/test/recovery/t/019_replslot_limit.pl | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/test/recovery/t/019_replslot_limit.pl b/src/test/recovery/t/019_replslot_limit.pl
index 54ddcef2bb..ee4801b49c 100644
--- a/src/test/recovery/t/019_replslot_limit.pl
+++ b/src/test/recovery/t/019_replslot_limit.pl
@@ -173,10 +173,20 @@ ok( !find_in_log(
         "requested WAL segment [0-9A-F]+ has already been removed"),
     'check that required WAL segments are still available');
 
-# Advance WAL again, the slot loses the oldest segment.
+# prevent checkpoints from occurring while advancing WAL segments
+$node_primary->safe_psql('postgres', "CHECKPOINT;");
+$node_primary->safe_psql('postgres',
+     "ALTER SYSTEM SET max_wal_size='40MB'; SELECT pg_reload_conf()");
+
+# Advance WAL again, the slot loses the oldest segment by the coming checkpoint.
 my $logstart = get_log_size($node_primary);
 advance_wal($node_primary, 7);
 
+# Cause a checkpoint
+$node_primary->safe_psql('postgres',
+     'ALTER SYSTEM RESET max_wal_size; SELECT pg_reload_conf()');
+$node_primary->safe_psql('postgres', "CHECKPOINT;");
+
 # wait until the WARNING is issued
 my $invalidated = 0;
 for (my $i = 0; $i < 10000; $i++)
-- 
2.27.0