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Commit9de9294

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Stop archive recovery if WAL generated with wal_level=minimal is found.
Previously if hot standby was enabled, archive recovery exited withan error when it found WAL generated with wal_level=minimal.But if hot standby was disabled, it just reported a warning andcontinued in that case. Which could lead to data loss or errorsduring normal operation. A warning was emitted, but users couldeasily miss that and not notice this serious situation untilthey encountered the actual errors.To improve this situation, this commit changes archive recoveryso that it exits with FATAL error when it finds WAL generated withwal_level=minimal whatever the setting of hot standby. This enablesusers to notice the serious situation soon.The FATAL error is thrown if archive recovery starts from a basebackup taken before wal_level is changed to minimal. When archiverecovery exits with the error, if users have a base backup takenafter setting wal_level to higher than minimal, they can recoverthe database by starting archive recovery from that newer backup.But note that if such backup doesn't exist, there is no easy way tocomplete archive recovery, which may make the database serverunstartable and users may lose whole database. The commit addsthe note about this risk into the document.Even in the case of unstartable database server, previously by justdisabling hot standby users could avoid the error during archiverecovery, forcibly start up the server and salvage data from it.But note that this commit makes this procedure unavailable at all.Author: Takamichi OsumiReviewed-by: Laurenz Albe, Kyotaro Horiguchi, David Steele, Fujii MasaoDiscussion:https://postgr.es/m/OSBPR01MB4888CBE1DA08818FD2D90ED8EDF90@OSBPR01MB4888.jpnprd01.prod.outlook.com
1 parentc4c393b commit9de9294

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4 files changed

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4 files changed

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‎doc/src/sgml/config.sgml

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@@ -2720,6 +2720,10 @@ include_dir 'conf.d'
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data from a base backup and the WAL logs, so <literal>replica</literal> or
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higher must be used to enable WAL archiving
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(<xref linkend="guc-archive-mode"/>) and streaming replication.
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Note that changing <varname>wal_level</varname> to
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<literal>minimal</literal> makes any base backups taken before
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unavailable for archive recovery and standby server, which may
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lead to database loss.
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</para>
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<para>
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In <literal>logical</literal> level, the same information is logged as

‎doc/src/sgml/perform.sgml

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@@ -1745,7 +1745,9 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
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<xref linkend="guc-wal-level"/> to <literal>minimal</literal>,
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<xref linkend="guc-archive-mode"/> to <literal>off</literal>, and
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<xref linkend="guc-max-wal-senders"/> to zero.
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But note that changing these settings requires a server restart.
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But note that changing these settings requires a server restart,
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and makes any base backups taken before unavailable for archive
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recovery and standby server, which may lead to database loss.
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</para>
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<para>

‎src/backend/access/transam/xlog.c

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@@ -6403,9 +6403,10 @@ CheckRequiredParameterValues(void)
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*/
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if (ArchiveRecoveryRequested&&ControlFile->wal_level==WAL_LEVEL_MINIMAL)
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{
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ereport(WARNING,
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(errmsg("WAL was generated with wal_level=minimal, data may be missing"),
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errhint("This happens if you temporarily set wal_level=minimal without taking a new base backup.")));
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ereport(FATAL,
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(errmsg("WAL was generated with wal_level=minimal, cannot continue recovering"),
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errdetail("This happens if you temporarily set wal_level=minimal on the server."),
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errhint("Use a backup taken after setting wal_level to higher than minimal.")));
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}
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/*
@@ -6414,11 +6415,6 @@ CheckRequiredParameterValues(void)
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*/
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if (ArchiveRecoveryRequested&&EnableHotStandby)
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{
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if (ControlFile->wal_level<WAL_LEVEL_REPLICA)
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ereport(ERROR,
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(errmsg("hot standby is not possible because wal_level was not set to \"replica\" or higher on the primary server"),
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errhint("Either set wal_level to \"replica\" on the primary, or turn off hot_standby here.")));
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/* We ignore autovacuum_max_workers when we make this test. */
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RecoveryRequiresIntParameter("max_connections",
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MaxConnections,
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# Test for archive recovery of WAL generated with wal_level=minimal
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use strict;
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use warnings;
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use PostgresNode;
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use TestLib;
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use Test::Moretests=> 2;
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use Time::HiResqw(usleep);
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# Initialize and start node with wal_level = replica and WAL archiving
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# enabled.
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my$node = get_new_node('orig');
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$node->init(has_archiving=> 1);
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my$replica_config =q[
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wal_level = replica
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archive_mode = on
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max_wal_senders = 10
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hot_standby = off
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];
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$node->append_conf('postgresql.conf',$replica_config);
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$node->start;
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# Take backup
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my$backup_name ='my_backup';
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$node->backup($backup_name);
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# Restart node with wal_level = minimal and WAL archiving disabled
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# to generate WAL with that setting. Note that such WAL has not been
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# archived yet at this moment because WAL archiving is not enabled.
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$node->append_conf(
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'postgresql.conf',q[
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wal_level = minimal
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archive_mode = off
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max_wal_senders = 0
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]);
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$node->restart;
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# Restart node with wal_level = replica and WAL archiving enabled
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# to archive WAL previously generated with wal_level = minimal.
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# We ensure the WAL file containing the record indicating the change
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# of wal_level to minimal is archived by checking pg_stat_archiver.
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$node->append_conf('postgresql.conf',$replica_config);
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$node->restart;
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# Find next WAL segment to be archived
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my$walfile_to_be_archived =$node->safe_psql('postgres',
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"SELECT pg_walfile_name(pg_current_wal_lsn());");
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# Make WAL segment eligible for archival
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$node->safe_psql('postgres','SELECT pg_switch_wal()');
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my$archive_wait_query
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="SELECT '$walfile_to_be_archived' <= last_archived_wal FROM pg_stat_archiver;";
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# Wait until the WAL segment has been archived.
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$node->poll_query_until('postgres',$archive_wait_query)
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ordie"Timed out while waiting for WAL segment to be archived";
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$node->stop;
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# Initialize new node from backup, and start archive recovery. Check that
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# archive recovery fails with an error when it detects the WAL record
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# indicating the change of wal_level to minimal and node stops.
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subtest_recovery_wal_level_minimal
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{
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my ($node_name,$node_text,$standby_setting) =@_;
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my$recovery_node = get_new_node($node_name);
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$recovery_node->init_from_backup(
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$node,$backup_name,
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has_restoring=> 1,standby=>$standby_setting);
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# Use run_log instead of recovery_node->start because this test expects
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# that the server ends with an error during recovery.
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run_log(
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['pg_ctl','-D',$recovery_node->data_dir,'-l',
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$recovery_node->logfile,'start']);
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# Wait up to 180s for postgres to terminate
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foreachmy$i (0 .. 1800)
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{
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lastif !-f$recovery_node->data_dir .'/postmaster.pid';
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usleep(100_000);
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}
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# Confirm that the archive recovery fails with an expected error
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my$logfile = slurp_file($recovery_node->logfile());
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ok($logfile =~
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qr/FATAL: WAL was generated with wal_level=minimal, cannot continue recovering/,
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"$node_text ends with an error because it finds WAL generated with wal_level=minimal");
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}
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# Test for archive recovery
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test_recovery_wal_level_minimal('archive_recovery','archive recovery', 0);
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# Test for standby server
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test_recovery_wal_level_minimal('standby','standby', 1);

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