v6-0005-Test-where-there-are-more-replication-slot-statis.patch

From f0453e6baefd0cf1ba0cd2537fdb46ac9371ce6b Mon Sep 17 00:00:00 2001
From: vignesh <vignesh21@gmail.com>
Date: Wed, 7 Apr 2021 13:07:26 +0530
Subject: [PATCH v6 5/5] Test where there are more replication slot statistics
 that max_replication_slot slots at startup.

There is a remote scenario where one of the replication slots is dropped and
the drop slot statistics message is not received by the statistic collector
process, now if the max_replication_slots is reduced to the actual number of
replication slots that are in use and the server is re-started then the
statistics process will not be aware of this and the statistic collector
process will write beyond the slots available, added a test for this.
---
 contrib/test_decoding/t/001_repl_stats.pl | 24 +++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/contrib/test_decoding/t/001_repl_stats.pl b/contrib/test_decoding/t/001_repl_stats.pl
index 194f764d18..932acee380 100644
--- a/contrib/test_decoding/t/001_repl_stats.pl
+++ b/contrib/test_decoding/t/001_repl_stats.pl
@@ -5,7 +5,7 @@ use warnings;
 use File::Path qw(rmtree);
 use PostgresNode;
 use TestLib;
-use Test::More tests => 2;
+use Test::More tests => 3;
 
 # Test set-up
 my $node = get_new_node('test');
@@ -100,12 +100,32 @@ is($result, qq(regression_slot1|t|t
 regression_slot2|t|t
 regression_slot3|t|t), 'check replication statistics are updated');
 
+# Test to remove one of the replication slots and adjust max_replication_slots
+# accordingly to the number of slots and verify replication statistics data is
+# fine after restart.
+$node->stop;
+my $datadir = $node->data_dir;
+my $slot3_replslotdir = "$datadir/pg_replslot/regression_slot3";
+
+rmtree($slot3_replslotdir);
+
+$node->append_conf('postgresql.conf', 'max_replication_slots = 2');
+$node->start;
+
+# Verify statistics data present in pg_stat_replication_slots are sane after
+# restart.
+$result = $node->safe_psql('postgres',
+	"SELECT slot_name, total_txns > 0 AS total_txn, total_bytes > 0 AS total_bytes FROM pg_stat_replication_slots ORDER BY slot_name"
+);
+is($result, qq(regression_slot1|t|t
+regression_slot2|t|t
+regression_slot3|t|t), 'check replication statistics are updated');
+
 # cleanup
 $node->safe_psql('postgres', "DROP TABLE test_repl_stat");
 $node->safe_psql('postgres', "DROP FUNCTION wait_for_decode_stats(TEXT)");
 $node->safe_psql('postgres', "SELECT pg_drop_replication_slot('regression_slot1')");
 $node->safe_psql('postgres', "SELECT pg_drop_replication_slot('regression_slot2')");
-$node->safe_psql('postgres', "SELECT pg_drop_replication_slot('regression_slot3')");
 
 # shutdown
 $node->stop;
-- 
2.25.1