
# Copyright (c) 2021, PostgreSQL Global Development Group

#
# Test situation where a target data directory contains
# WAL records beyond both the last checkpoint and the divergence
# point:
#
# Target WAL (TLI 2):
#
# backup ... Checkpoint A ... INSERT 'rewind this'
#            (TLI 1 -> 2)
#
#            ^ last common                        ^ minRecoveryPoint
#              checkpoint
#
# Source WAL (TLI 3):
#
# backup ... Checkpoint A ... Checkpoint B ... INSERT 'keep this'
#            (TLI 1 -> 2)     (TLI 2 -> 3)
#
#
# The last common checkpoint is Checkpoint A. But there is WAL on TLI 2
# after the last common checkpoint that needs to be rewound. We used to
# have a bug where minRecoveryPoint was ignored, and pg_rewind concluded
# that the target doesn't need rewinding in this scenario, because the
# last checkpoint on the target TLI was an ancestor of the source TLI.
#
#
# This test does not make use of RewindTest as it requires three
# nodes.

use strict;
use warnings;
use PostgresNode;
use TestLib;
use Test::More tests => 3;

use File::Copy;

my $tmp_folder = TestLib::tempdir;

my $node_1 = get_new_node('node_1');
$node_1->init(allows_streaming => 1);
$node_1->append_conf(
	'postgresql.conf', qq(
wal_keep_size='100 MB'
));

$node_1->start;

# Create a couple of test tables
$node_1->safe_psql('postgres', 'CREATE TABLE public.foo (t TEXT)');
$node_1->safe_psql('postgres', 'CREATE TABLE public.bar (t TEXT)');
$node_1->safe_psql('postgres', "INSERT INTO public.bar VALUES ('in both')");

#
# Create node_2 and node_3 as standbys following node_1
#
my $backup_name = 'my_backup';
$node_1->backup($backup_name);

my $node_2 = get_new_node('node_2');
$node_2->init_from_backup($node_1, $backup_name, has_streaming => 1);
$node_2->start;

my $node_3 = get_new_node('node_3');
$node_3->init_from_backup($node_1, $backup_name, has_streaming => 1);
$node_3->start;

# Wait until node 3 has connected and caught up
my $lsn = $node_1->lsn('insert');
$node_1->wait_for_catchup('node_3', 'replay', $lsn);

#
# Swap the roles of node_1 and node_3, so that node_1 follows node_3.
#
$node_1->stop('fast');
$node_3->promote;
# Force a checkpoint after the promotion. pg_rewind looks at the control
# file to determine what timeline the server is on, and that isn't updated
# immediately at promotion, but only at the next checkpoint. When running
# pg_rewind in remote mode, it's possible that we complete the test steps
# after promotion so quickly that when pg_rewind runs, the standby has not
# performed a checkpoint after promotion yet.
$node_3->safe_psql('postgres', "checkpoint");

# reconfigure node_1 as a standby following node_3
my $node_3_connstr = $node_3->connstr;
$node_1->append_conf(
	'postgresql.conf', qq(
primary_conninfo='$node_3_connstr'
));
$node_1->set_standby_mode();
$node_1->start();

# also reconfigure node_2 to follow node_3
$node_2->append_conf(
	'postgresql.conf', qq(
primary_conninfo='$node_3_connstr'
));
$node_2->restart();

#
# Promote node_1, to create a split-brain scenario.
#

# make sure node_1 is full caught up with node_3 first
$lsn = $node_3->lsn('insert');
$node_3->wait_for_catchup('node_1', 'replay', $lsn);

$node_1->promote;
# Force a checkpoint after promotion, like earlier.
$node_1->safe_psql('postgres', "checkpoint");

#
# We now have a split-brain with two primaries. Insert a row on both to
# demonstratively create a split brain. After the rewind, we should only
# see the insert on 1, as the insert on node 3 is rewound away.
#
$node_1->safe_psql('postgres',
	"INSERT INTO public.foo (t) VALUES ('keep this')");
# 'bar' is unmodified in node 1, so it won't be overwritten by replaying the
# WAL from node 1.
$node_3->safe_psql('postgres',
	"INSERT INTO public.bar (t) VALUES ('rewind this')");

# Insert more rows in node 1, to bump up the XID counter. Otherwise, if
# rewind doesn't correctly rewind the changes made on the other node,
# we might fail to notice if the inserts are invisible because the XIDs
# are not marked as committed.
$node_1->safe_psql('postgres',
	"INSERT INTO public.foo (t) VALUES ('and this')");
$node_1->safe_psql('postgres',
	"INSERT INTO public.foo (t) VALUES ('and this too')");

# Wait for node 2 to catch up
$node_2->poll_query_until('postgres',
	q|SELECT COUNT(*) > 1 FROM public.bar|, 't');

# At this point node_2 will shut down without a shutdown checkpoint,
# but with WAL entries beyond the preceding shutdown checkpoint.
$node_2->stop('fast');
$node_3->stop('fast');

my $node_2_pgdata  = $node_2->data_dir;
my $node_1_connstr = $node_1->connstr;

# Keep a temporary postgresql.conf or it would be overwritten during the rewind.
copy(
	"$node_2_pgdata/postgresql.conf",
	"$tmp_folder/node_2-postgresql.conf.tmp");

command_ok(
	[
		'pg_rewind',                      "--source-server=$node_1_connstr",
		"--target-pgdata=$node_2_pgdata", "--debug"
	],
	'run pg_rewind');

# Now move back postgresql.conf with old settings
move(
	"$tmp_folder/node_2-postgresql.conf.tmp",
	"$node_2_pgdata/postgresql.conf");

$node_2->start;

# Check contents of the test tables after rewind. The rows inserted in node 3
# before rewind should've been overwritten with the data from node 1.
my $result;
$result = $node_2->safe_psql('postgres', 'SELECT * FROM public.foo');
is( $result, qq(keep this
and this
and this too), 'table foo after rewind');

$result = $node_2->safe_psql('postgres', 'SELECT * FROM public.bar');
is($result, qq(in both), 'table bar after rewind');
