Date: Thu, 09 Apr 2020 10:13:39 +0900 (JST)
Message-Id: <20200409.101339.1252894237035894186.horikyota.ntt@gmail.com>
To: alvherre@alvh.no-ip.org
Cc: pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Remove testing for precise LSN/reserved bytes in new
 TAP test
From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
In-Reply-To: <20200408.144452.1031907626229663626.horikyota.ntt@gmail.com>
References: <E1jM1Sa-0003mS-99@gemulon.postgresql.org>
	<20200408.144452.1031907626229663626.horikyota.ntt@gmail.com>
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At Wed, 08 Apr 2020 14:44:52 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> At Wed, 08 Apr 2020 03:33:04 +0000, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote in 
> > Remove testing for precise LSN/reserved bytes in new TAP test
> > 
> > Trying to ensure that a slot's restart_lsn or amount of reserved bytes
> > exactly match some specific values seems unnecessary, and fragile as
> > shown by failures in multiple buildfarm members.
> 
> Sorry for the wrong test file.
> Checking in lower precision would be sufficient.

I noticed that prailiedog failed in another mode.


not ok 5 - check that max_slot_wal_keep_size is working

#   Failed test 'check that max_slot_wal_keep_size is working'
#   at t/019_replslot_limit.pl line 89.
#          got: '0/D00198|normal|5120 kB'
#     expected: '0/D00164|normal|5120 kB'

The first colomn in the result is restart_lsn and it's not essential
to the test. It is removed in the attached test script. Precise LSN is
not reffered in tht test script.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

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# Test for replication slot limit
# Ensure that max_slot_wal_keep_size limits the number of WAL files to
# be kept by replication slots.
use strict;
use warnings;

use TestLib;
use PostgresNode;

use File::Path qw(rmtree);
use Test::More tests => 13;
use Time::HiRes qw(usleep);

$ENV{PGDATABASE} = 'postgres';

# Initialize master node, setting wal-segsize to 1MB
my $node_master = get_new_node('master');
$node_master->init(allows_streaming => 1, extra => ['--wal-segsize=1']);
$node_master->append_conf('postgresql.conf', qq(
min_wal_size = 2MB
max_wal_size = 4MB
log_checkpoints = yes
));
$node_master->start;
$node_master->safe_psql('postgres', "SELECT pg_create_physical_replication_slot('rep1')");

# The slot state and remain should be null before the first connection
my $result = $node_master->safe_psql('postgres', "SELECT restart_lsn is NULL, wal_status is NULL, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "t|t|t", 'check the state of non-reserved slot is "unknown"');


# Take backup
my $backup_name = 'my_backup';
$node_master->backup($backup_name);

# Create a standby linking to it using the replication slot
my $node_standby = get_new_node('standby_1');
$node_standby->init_from_backup($node_master, $backup_name, has_streaming => 1);
$node_standby->append_conf('postgresql.conf', "primary_slot_name = 'rep1'");

$node_standby->start;

# Wait until standby has replayed enough data
my $start_lsn = $node_master->lsn('write');
$node_master->wait_for_catchup($node_standby, 'replay', $start_lsn);

# Stop standby
$node_standby->stop;

# Preparation done, the slot is the state "normal" now
$result = $node_master->safe_psql('postgres', "SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "normal|t", 'check the catching-up state');

# Advance WAL by five segments (= 5MB) on master
advance_wal($node_master, 1);
$node_master->safe_psql('postgres', "CHECKPOINT;");

# The slot is always "safe" when fitting max_wal_size
$result = $node_master->safe_psql('postgres', "SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "normal|t", 'check that it is safe if WAL fits in max_wal_size');

advance_wal($node_master, 4);
$node_master->safe_psql('postgres', "CHECKPOINT;");

# The slot is always "safe" when max_slot_wal_keep_size is not set
$result = $node_master->safe_psql('postgres', "SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "normal|t", 'check that slot is working');

# The standby can reconnect to master
$node_standby->start;

$start_lsn = $node_master->lsn('write');
$node_master->wait_for_catchup($node_standby, 'replay', $start_lsn);

$node_standby->stop;

# Set max_slot_wal_keep_size on master
my $max_slot_wal_keep_size_mb = 6;
$node_master->append_conf('postgresql.conf', qq(
max_slot_wal_keep_size = ${max_slot_wal_keep_size_mb}MB
));
$node_master->reload;

# The slot is in safe state. The distance from the min_safe_lsn should
# be as almost (max_slot_wal_keep_size - 1) times large as the segment
# size

$result = $node_master->safe_psql('postgres', "SELECT wal_status, floor((pg_current_wal_lsn() - min_safe_lsn) / 1024 / 1024) FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "normal|5", 'check that max_slot_wal_keep_size is working');

# Advance WAL again then checkpoint, reducing remain by 2 MB.
advance_wal($node_master, 2);
$node_master->safe_psql('postgres', "CHECKPOINT;");

# The slot is still working
$result = $node_master->safe_psql('postgres', "SELECT wal_status, floor((pg_current_wal_lsn() - min_safe_lsn) / 1024 / 1024) FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "normal|2", 'check that min_safe_lsn gets close to the current LSN');

# The standby can reconnect to master
$node_standby->start;
$start_lsn = $node_master->lsn('write');
$node_master->wait_for_catchup($node_standby, 'replay', $start_lsn);
$node_standby->stop;

# wal_keep_segments overrides max_slot_wal_keep_size
$result = $node_master->safe_psql('postgres', "ALTER SYSTEM SET wal_keep_segments to 8; SELECT pg_reload_conf();");
# Advance WAL again then checkpoint, reducing remain by 6 MB.
advance_wal($node_master, 6);
$result = $node_master->safe_psql('postgres', "SELECT wal_status, floor((pg_current_wal_lsn() - min_safe_lsn) / 1024 / 1024) as remain FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "normal|8", 'check that wal_keep_segments overrides max_slot_wal_keep_size');
# restore wal_keep_segments
$result = $node_master->safe_psql('postgres', "ALTER SYSTEM SET wal_keep_segments to 0; SELECT pg_reload_conf();");

# The standby can reconnect to master
$node_standby->start;
$start_lsn = $node_master->lsn('write');
$node_master->wait_for_catchup($node_standby, 'replay', $start_lsn);
$node_standby->stop;

# Advance WAL again without checkpoint, reducing remain by 6 MB.
advance_wal($node_master, 6);

# Slot gets into 'reserved' state
$result = $node_master->safe_psql('postgres', "SELECT wal_status, floor((pg_current_wal_lsn() - min_safe_lsn) / 1024 / 1024) FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "reserved|6", 'check that the slot state changes to "reserved"');

# do checkpoint so that the next checkpoint runs too early
$node_master->safe_psql('postgres', "CHECKPOINT;");

# Advance WAL again without checkpoint; remain goes to 0.
advance_wal($node_master, 1);

# Slot gets into 'lost' state
$result = $node_master->safe_psql('postgres', "SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "lost|t", 'check that the slot state changes to "lost"');

# The standby still can connect to master before a checkpoint
$node_standby->start;

$start_lsn = $node_master->lsn('write');
$node_master->wait_for_catchup($node_standby, 'replay', $start_lsn);

$node_standby->stop;

ok(!find_in_log($node_standby,
				"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.
my $logstart = get_log_size($node_master);
advance_wal($node_master, 7);
$node_master->safe_psql('postgres', "CHECKPOINT;");

# WARNING should be issued
ok(find_in_log($node_master,
			   "invalidating slot \"rep1\" because its restart_lsn [0-9A-F/]+ exceeds max_slot_wal_keep_size",
			   $logstart),
   'check that the warning is logged');

# This slot should be broken
$result = $node_master->safe_psql('postgres', "SELECT slot_name, active, restart_lsn, wal_status, min_safe_lsn FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "rep1|f|||", 'check that the slot became inactive');

# The standby no longer can connect to the master
$logstart = get_log_size($node_standby);
$node_standby->start;

my $failed = 0;
for (my $i = 0; $i < 10000; $i++)
{
	if (find_in_log($node_standby,
					"requested WAL segment [0-9A-F]+ has already been removed",
					$logstart))
	{
		$failed = 1;
		last;
	}
	usleep(100_000);
}
ok($failed, 'check that replication has been broken');

$node_standby->stop;

#####################################
# Advance WAL of $node by $n segments
sub advance_wal
{
	my ($node, $n) = @_;

	# Advance by $n segments (= (16 * $n) MB) on master
	for (my $i = 0 ; $i < $n ; $i++)
	{
		$node->safe_psql('postgres', "CREATE TABLE t (); DROP TABLE t; SELECT pg_switch_wal();");
	}
	return;
}

# return the size of logfile of $node in bytes
sub get_log_size
{
	my ($node) = @_;

	return (stat $node->logfile)[7];
}

# find $pat in logfile of $node after $off-th byte
sub find_in_log
{
	my ($node, $pat, $off) = @_;

	$off = 0 unless defined $off;
	my $log = TestLib::slurp_file($node->logfile);
	return 0 if (length($log) <= $off);

	$log = substr($log, $off);

	return $log =~ m/$pat/;
}

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