From 41cce2326135c05d6db311ad894703c3080be33c Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Wed, 13 Oct 2021 18:49:27 -0300
Subject: [PATCH] Change recently added test code for stability

The test code added with ff9f111bce24 fails under valgrind, and probably
other slow cases too, because if (say) autovacuum runs in between and
produces WAL of its own, the large INSERT fails to account for that in
the LSN calculations.  Rewrite to use a DO loop.

Per complaint from Andres Freund

Backpatch to all branches.

Discussion: https://postgr.es/m/20211013180338.5guyqzpkcisqugrl@alap3.anarazel.de
---
 .../recovery/t/026_overwrite_contrecord.pl    | 48 +++++++++----------
 1 file changed, 24 insertions(+), 24 deletions(-)

diff --git a/src/test/recovery/t/026_overwrite_contrecord.pl b/src/test/recovery/t/026_overwrite_contrecord.pl
index 645f398108e..c448a3f542a 100644
--- a/src/test/recovery/t/026_overwrite_contrecord.pl
+++ b/src/test/recovery/t/026_overwrite_contrecord.pl
@@ -22,34 +22,34 @@ $node->init(allows_streaming => 1);
 $node->append_conf('postgresql.conf', 'wal_keep_segments=16');
 $node->start;
 
-$node->safe_psql('postgres', 'create table filler (a int)');
-
-# First, measure how many bytes does the insertion of 1000 rows produce
-my $start_lsn =
-  $node->safe_psql('postgres', q{select pg_current_wal_insert_lsn() - '0/0'});
-$node->safe_psql('postgres',
-	'insert into filler select * from generate_series(1, 1000)');
-my $end_lsn =
-  $node->safe_psql('postgres', q{select pg_current_wal_insert_lsn() - '0/0'});
-my $rows_walsize = $end_lsn - $start_lsn;
+$node->safe_psql('postgres', 'create table filler (a int, b text)');
 
 # Now consume all remaining room in the current WAL segment, leaving
 # space enough only for the start of a largish record.
 $node->safe_psql(
-	'postgres', qq{
-WITH segsize AS (
-  SELECT setting::int
-    FROM pg_settings WHERE name = 'wal_segment_size'
-), walblksz AS (
-  SELECT setting::int
-    FROM pg_settings WHERE name = 'wal_block_size'
-), setting AS (
-  SELECT segsize.setting * walblksz.setting AS wal_segsize
-    FROM segsize, walblksz
-)
-INSERT INTO filler
-SELECT g FROM setting,
-  generate_series(1, 1000 * (wal_segsize - ((pg_current_wal_insert_lsn() - '0/0') % wal_segsize)) / $rows_walsize) g
+	'postgres', q{
+DO $$
+DECLARE
+    wal_segsize int :=
+        (max(setting) filter (where name = 'wal_segment_size'))::int *
+        (max(setting) filter (where name = 'wal_block_size'))::int from pg_settings ;
+    remain int;
+    iters  int := 0;
+BEGIN
+    LOOP
+        INSERT into filler
+        select g, repeat(md5(g::text), (random() * 60 + 1)::int)
+        from generate_series(1, 10) g;
+
+        remain := wal_segsize - (pg_current_wal_insert_lsn() - '0/0') % wal_segsize;
+        IF remain < 2 * setting::int from pg_settings where name = 'block_size' THEN
+            RAISE log 'exiting after % iterations, % bytes to end of WAL segment', iters, remain;
+            EXIT;
+        END IF;
+        iters := iters + 1;
+    END LOOP;
+END
+$$;
 });
 
 my $initfile = $node->safe_psql('postgres',