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Re: 9.1 doesn't start when died mid-backup

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: depesz(at)depesz(dot)com
Cc: pgsql-bugs(at)postgresql(dot)org, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Subject: Re: 9.1 doesn't start when died mid-backup
Date: 2011-04-13 11:18:30
Message-ID: 4DA58686.1050501@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-bugs
On 13.04.2011 10:49, hubert depesz lubaczewski wrote:
> hi
> got new 9.1, straight from git.
> compiled, installed.
> did initdb, and then set config values using this script:
> perl -pi -e '
>    s/\A \s* (?: [#] \s* )? listen_addresses \s* = \s*.*/listen_addresses = \047*\047/x;
>    s/\A \s* (?: [#] \s* )? log_destination \s* = \s*.*/log_destination = \047stderr\047/x;
>    s/\A \s* (?: [#] \s* )? logging_collector \s* = \s*.*/logging_collector = on/x;
>    s/\A \s* (?: [#] \s* )? log_min_duration_statement \s* = \s*.*/log_min_duration_statement = 0/x;
>    s/\A \s* (?: [#] \s* )? log_line_prefix \s* = \s*.*/log_line_prefix = \047\%m \%u\(at)\%d \%p \%r \047/x;
>    s/\A \s* (?: [#] \s* )? log_temp_files \s* = \s*.*/log_temp_files = 0/x;
>    s/\A \s* (?: [#] \s* )? (log_checkpoints|log_connections|log_disconnections|log_lock_waits) \s* = \s*.*/$1 = on/x;
>    s/\A \s* (?: [#] \s* )? wal_level \s* = \s*.*/wal_level = hot_standby/x;
>    s/\A \s* (?: [#] \s* )? archive_mode \s* = \s*.*/archive_mode = on/x;
>    s/\A \s* (?: [#] \s* )? archive_command \s* = \s*.*/archive_command = \047\/bin\/true\047/x;
> ' data/postgresql.conf
>
> afterwards I did start pg.
>
> then, i connected with psql, and issued:
> $ select pg_start_backup('xx');
>   pg_start_backup
> -----------------
>   0/2000020
> (1 row)
>
> $ create database pgdba;
> CREATE DATABASE
>
> $ create user postgres with superuser;
> CREATE ROLE
>
> $ create user depesz with superuser;
> CREATE ROLE
>
> $ create database depesz with owner depesz;
> CREATE DATABASE
>
> Afterwards, I exited psql, and simulated power-failure, with:
>
> =$ killall -9 postgres; killall -9 postmaster
> postmaster: no process found
>
> All pg processes were killed.
>
> When I then tried to start Pg, I got:
> =$ pg_ctl start
> pg_ctl: another server might be running; trying to start server anyway
> server starting
>
> but it didn't start.
>
> log looks like this:
> =$ cat postgresql-2011-04-13_093859.log
> 2011-04-13 09:38:59.807 CEST @ 3446  LOG:  database system was interrupted; last known up at 2011-04-13 09:38:43 CEST
> 2011-04-13 09:38:59.807 CEST @ 3446  LOG:  database system was not properly shut down; automatic recovery in progress
> 2011-04-13 09:38:59.852 CEST @ 3446  LOG:  redo starts at 0/2000020
> 2011-04-13 09:39:00.304 CEST @ 3446  LOG:  record with zero length at 0/20018E8
> 2011-04-13 09:39:00.304 CEST @ 3446  LOG:  redo done at 0/2001898
> 2011-04-13 09:39:00.304 CEST @ 3446  LOG:  last completed transaction was at log time 2011-04-13 09:38:43.563356+02
> 2011-04-13 09:39:00.304 CEST @ 3446  FATAL:  WAL ends before end of online backup
> 2011-04-13 09:39:00.304 CEST @ 3446  HINT:  Online backup started with pg_start_backup() must be ended with pg_stop_backup(), and all WAL up to that point must be available at recovery.
> 2011-04-13 09:39:00.304 CEST @ 3444  LOG:  startup process (PID 3446) exited with exit code 1
> 2011-04-13 09:39:00.304 CEST @ 3444  LOG:  aborting startup due to startup process failure
>
> interestingl7y backup_label got renamed to backup_label.old, and
> contains:
> START WAL LOCATION: 0/2000020 (file 000000010000000000000002)
> CHECKPOINT LOCATION: 0/2000058
> START TIME: 2011-04-13 09:38:19 CEST
> LABEL: xx
>
> Given the file was renamed, I retried:
>
> =$ pg_ctl start
> server starting
>
> but again - it didn't work.
>
> Log looks like this:
>
> 2011-04-13 09:44:06.844 CEST @ 3783  LOG:  database system was interrupted while in recovery at 2011-04-13 09:38:59 CEST
> 2011-04-13 09:44:06.844 CEST @ 3783  HINT:  This probably means that some data is corrupted and you will have to use the last backup for recovery.
> 2011-04-13 09:44:06.845 CEST @ 3783  LOG:  database system was not properly shut down; automatic recovery in progress
> 2011-04-13 09:44:06.877 CEST @ 3783  LOG:  redo starts at 0/2000020
> 2011-04-13 09:44:07.316 CEST @ 3783  LOG:  record with zero length at 0/20018E8
> 2011-04-13 09:44:07.316 CEST @ 3783  LOG:  redo done at 0/2001898
> 2011-04-13 09:44:07.316 CEST @ 3783  LOG:  last completed transaction was at log time 2011-04-13 09:38:43.563356+02
> 2011-04-13 09:44:07.316 CEST @ 3783  FATAL:  WAL ends before end of online backup
> 2011-04-13 09:44:07.316 CEST @ 3783  HINT:  Online backup started with pg_start_backup() must be ended with pg_stop_backup(), and all WAL up to that point must be available at recovery.
> 2011-04-13 09:44:07.316 CEST @ 3776  LOG:  startup process (PID 3783) exited with exit code 1
> 2011-04-13 09:44:07.316 CEST @ 3776  LOG:  aborting startup due to startup process failure
>
>
> So, it looks to me that by killing postgres mid-backup I made it end up in some state that doesn't let it start again.
>
> I *think* it might be related to this:
> http://archives.postgresql.org/pgsql-hackers/2011-03/msg01490.php and more
> specifically, with this:
> http://archives.postgresql.org/pgsql-hackers/2011-03/msg01627.php

Yep :-(. I'm thinking we need to revert that change, now that we know 
there was a reason for only checking the end-of-WAL when doing archive 
recovery after all. We can keep it as a warning, though. With a hint 
explaining that if you're doing crash recovery from a database that 
crashed while an online backup was in progress, it's ok, but if you're 
recovering from an online backup, the backup is broken.

For backups taken with pg_basebackup in 9.1, we can add a flag to the 
backup_label, indicating that the backup was taken with pg_basebackup. 
For such backups, the above scenario really should not happen, and we 
can still make it a hard error if it does.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

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