Thread: [GENERAL] autovacuum holds exclusive lock on table preventing it from to beupdated
[GENERAL] autovacuum holds exclusive lock on table preventing it from to beupdated
From
Dmitry O Litvintsev
Date:
Hi,
I run postgresql 9.3.17. I am preparing for a major database schema upgrade.
I copied production database to test system using pg_basebackup.
Having started the database and waited for all WALs to be applied I proceeded to run
schema modifications.
Immediately I run into issue - updates on a table get stuck because I see that autovacuum is running
on that table and it holds exclusive lock:
datname | relname | transactionid | mode | granted | usename |
substr | query_start | age | pid
---------+----------------------------+---------------+--------------------------+---------+---------+---------------------------------------------------------------------------+-------------------------------+-----------------+-------
chimera | t_inodes_itype_idx | | RowExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:25:22.285415 | 40672
chimera | t_inodes_imtime_idx | | RowExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:25:22.285415 | 40672
chimera | t_inodes_iio_idx | | RowExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:25:22.285415 | 40672
chimera | t_inodes_pkey | | RowExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:25:22.285415 | 40672
chimera | | | ExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:25:22.285415 | 40672
chimera | t_inodes | | ShareUpdateExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound)
If I killed autovacuum (by running SELECT pg_cancel_backend(PID) , I get at an update going, but then another update
wouldget stuck by autovacuum launching again).
I tried to set autovacuum to off (together w/ track_counts) and conf file. After restart , autovacuum still runs !
chimera=# show autovacuum;
autovacuum
------------
off
(1 row)
checking activity :
chimera=# select pg_stat_activity.datname,pg_class.relname,pg_locks.transactionid,
pg_locks.mode, pg_locks.granted,pg_stat_activity.usename,
substr(pg_stat_activity.query,1,256),
pg_stat_activity.query_start, age(now(),pg_stat_activity.query_start) as "age",
pg_stat_activity.pid from pg_stat_activity,pg_locks
left outer join pg_class on (pg_locks.relation = pg_class.oid)
where pg_locks.pid=pg_stat_activity.pid order by query_start;
shows autovacuum. Seems like setting it to off does not take any effect.
datname | relname | transactionid | mode | granted | usename |
substr | query_start | age | pid
---------+----------------------------+---------------+--------------------------+---------+---------+---------------------------------------------------------------------------+-------------------------------+-----------------+-------
chimera | t_inodes_itype_idx | | RowExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:28:50.276437 | 40672
chimera | t_inodes_imtime_idx | | RowExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:28:50.276437 | 40672
chimera | t_inodes_iio_idx | | RowExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:28:50.276437 | 40672
chimera | t_inodes_pkey | | RowExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:28:50.276437 | 40672
chimera | | | ExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:28:50.276437 | 40672
chimera | t_inodes | | ShareUpdateExclusiveLock | t | enstore | autovacuum:
VACUUMpublic.t_inodes (to prevent wraparound) | 2017-06-13 12:31:04.870064-05 | 00:28:50.276437 | 40672
Anything I am doing wrong or is this a bug (or feature). The issue - autovacuum blocks table updates and I cannot turn
theautovacuum off.
Dmitry
Re: [GENERAL] autovacuum holds exclusive lock on table preventing it from to be updated
From
Andreas Kretschmer
Date:
Am 13. Juni 2017 20:04:04 MESZ schrieb Dmitry O Litvintsev <litvinse@fnal.gov>: > >I >wraparound) | 2017- >| t | enstore | autovacuum: VACUUM public.t_inodes (to prevent >wraparound) | 2017-06-13 12:31:04.870064-05 | >00:28:50.276437 | 40672 >chimera | t_inodes | | >ShareUpdateExclusiveLock | t | enstore | autovacuum: VACUUM >public.t_inodes (to prevent wraparound) | 2017-06-13 >12:31:04.870064-05 | 00:28:50.276437 | 40672 > It is a autocacuum to prevent wraparound, you can't stop or avoid that. Regards, Andreas -- Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail gesendet.
Re: [GENERAL] autovacuum holds exclusive lock on table preventing itfrom to be updated
From
Dmitry O Litvintsev
Date:
Hi
Since I have posted this nothing really changed. I am starting to panic (mildly).
The source (production) runs :
relname | mode | granted | substr
| query_start | age
----------------------------+--------------------------+---------+----------------------------------------------------------------------+-------------------------------+------------------------
t_inodes_iio_idx | RowExclusiveLock | t | autovacuum: VACUUM ANALYZE public.t_inodes (to
preventwraparound) | 2017-06-15 10:26:18.643209-05 | 4 days 01:58:56.697559
t_inodes_pkey | RowExclusiveLock | t | autovacuum: VACUUM ANALYZE public.t_inodes (to
preventwraparound) | 2017-06-15 10:26:18.643209-05 | 4 days 01:58:56.697559
| ExclusiveLock | t | autovacuum: VACUUM ANALYZE public.t_inodes (to
preventwraparound) | 2017-06-15 10:26:18.643209-05 | 4 days 01:58:56.697559
t_inodes | ShareUpdateExclusiveLock | t | autovacuum: VACUUM ANALYZE public.t_inodes (to
preventwraparound) | 2017-06-15 10:26:18.643209-05 | 4 days 01:58:56.697559
t_inodes_itype_idx | RowExclusiveLock | t | autovacuum: VACUUM ANALYZE public.t_inodes (to
preventwraparound) | 2017-06-15 10:26:18.643209-05 | 4 days 01:58:56.697559
t_inodes_imtime_idx | RowExclusiveLock | t | autovacuum: VACUUM ANALYZE public.t_inodes (to
preventwraparound) | 2017-06-15 10:26:18.643209-05 | 4 days 01:58:56.697559
Above does not impact production activity a lot.
On the test stand (where I pg_basebackupped from production and also upgraded to 9.6) I see:
relname | mode | granted | substr
| query_start | age
-----------------------------------+--------------------------+---------+------------------------------------------------------------+-------------------------------+------------------------
t_inodes | ShareUpdateExclusiveLock | t | autovacuum: VACUUM public.t_inodes (to
preventwraparound) | 2017-06-13 15:27:54.872154-05 | 5 days 20:59:22.769404
t_inodes_itype_idx | RowExclusiveLock | t | autovacuum: VACUUM public.t_inodes (to
preventwraparound) | 2017-06-13 15:27:54.872154-05 | 5 days 20:59:22.769404
t_inodes_imtime_idx | RowExclusiveLock | t | autovacuum: VACUUM public.t_inodes (to
preventwraparound) | 2017-06-13 15:27:54.872154-05 | 5 days 20:59:22.769404
t_inodes_iio_idx | RowExclusiveLock | t | autovacuum: VACUUM public.t_inodes (to
preventwraparound) | 2017-06-13 15:27:54.872154-05 | 5 days 20:59:22.769404
t_inodes_pkey | RowExclusiveLock | t | autovacuum: VACUUM public.t_inodes (to
preventwraparound) | 2017-06-13 15:27:54.872154-05 | 5 days 20:59:22.769404
| ExclusiveLock | t | autovacuum: VACUUM public.t_inodes (to
preventwraparound) | 2017-06-13 15:27:54.872154-05 | 5 days 20:59:22.769404
t_inodes | ShareUpdateExclusiveLock | f | ANALYZE;
| 2017-06-13 15:27:59.781285-05 | 5 days 20:59:17.860273
| ExclusiveLock | t | ANALYZE;
| 2017-06-13 15:27:59.781285-05 | 5 days 20:59:17.860273
The test stand where I was to test schema upgrade is stuck cuz vacuum is blocking.
Production settings follow:
version 9.3.9
max_connections = 512
shared_buffers = 8192MB
temp_buffers = 1024MB
work_mem = 512MB
#maintenance_work_mem = 2048MB
maintenance_work_mem = 4096MB #increased after 3 days of vacuum analyze running
max_stack_depth = 2MB
vacuum_cost_delay = 50ms
synchronous_commit = off
wal_buffers = 245MB
wal_writer_delay = 10s
checkpoint_segments = 64
checkpoint_completion_target = 0.9
random_page_cost = 2.0
effective_cache_size = 94GB
wal_level = hot_standby
hot_standby = on
archive_mode = on
archive_command = '/usr/loca/bin/wal_backup.sh %p %f'
max_wal_senders = 4
wal_keep_segments = 1024
max_standby_streaming_delay = 7200s
So, the problem : I cannot do schema change until vacuum has finished, and there
seems to be no end in sight for vacuum to finish throwing off our software upgrade plans.
Anything can be done here?
Thanks,
Dmitry
________________________________________
From: Andreas Kretschmer <andreas@a-kretschmer.de>
Sent: Tuesday, June 13, 2017 1:54 PM
To: pgsql-general@postgresql.org; Dmitry O Litvintsev; pgsql-general@postgresql.org
Subject: Re: [GENERAL] autovacuum holds exclusive lock on table preventing it from to be updated
Am 13. Juni 2017 20:04:04 MESZ schrieb Dmitry O Litvintsev <litvinse@fnal.gov>:
>
>I
>wraparound) | 2017-
>| t | enstore | autovacuum: VACUUM public.t_inodes (to prevent
>wraparound) | 2017-06-13 12:31:04.870064-05 |
>00:28:50.276437 | 40672
>chimera | t_inodes | |
>ShareUpdateExclusiveLock | t | enstore | autovacuum: VACUUM
>public.t_inodes (to prevent wraparound) | 2017-06-13
>12:31:04.870064-05 | 00:28:50.276437 | 40672
>
It is a autocacuum to prevent wraparound, you can't stop or avoid that.
Regards, Andreas
--
Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail gesendet.
Re: [GENERAL] autovacuum holds exclusive lock on table preventing itfrom to be updated
From
Alvaro Herrera
Date:
Dmitry O Litvintsev wrote: > Hi > > Since I have posted this nothing really changed. I am starting to panic (mildly). ... > vacuum_cost_delay = 50ms Most likely, this value is far too high. You're causing autovacuum to sleep for a very long time with this setting. Hard to say for certain without seeing the cost_limit value and the other related parameters, but it's most certainly what's causing you pain. The default of 20ms is already too high for most users. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Re: [GENERAL] autovacuum holds exclusive lock on table preventing itfrom to be updated
From
Jeff Janes
Date:
On Mon, Jun 19, 2017 at 10:33 AM, Dmitry O Litvintsev <litvinse@fnal.gov> wrote:
Hi
Since I have posted this nothing really changed. I am starting to panic (mildly).
The source (production) runs :
relname | mode | granted | substr | query_start | age
----------------------------+--------------------------+---- -----+------------------------ ------------------------------ ----------------+------------- ------------------+----------- -------------
t_inodes_iio_idx | RowExclusiveLock | t | autovacuum: VACUUM ANALYZE public.t_inodes (to prevent wraparound) | 2017-06-15 10:26:18.643209-05 | 4 days 01:58:56.697559
This is close to unreadable. You can use use \x to get output from psql which survives email more readably.
Your first report was 6 days ago. Why is the job only 4 days old? Are you frequently restarting your production server, so that the vacuum job never gets a chance to finish? If so, that would explain your predicament.
And how big is this table, that it takes at least 4 days to VACUUM?
vacuum_cost_delay = 50ms
That is a lot. The default value for this is 0. The default value for autovacuum_vacuum_cost_delay is 20, which is usually too high for giant databases.
I think you are changing this in the wrong direction. Rather than increase vacuum_cost_delay, you need to decrease autovacuum_vacuum_cost_delay, so that you won't keep having problems in the future.
On your test server, change vacuum_cost_delay to zero and then initiate a manual vacuum of the table. It will block on the autovacuum's lock, so then kill the autovacuum (best to have the manual vacuum queued up first, otherwise it will be race between when you start the manual vacuum, and when the autovacuum automatically restarts, to see who gets the lock). See how long it takes this unthrottled vacuum to run, and how much effect the IO it causes has on the performance of other tasks. If acceptable, repeat this on production (although really, I don't that you have much of a choice on whether the effect it is acceptable or not--it needs to be done.)
Cheers,
Jeff
Re: [GENERAL] autovacuum holds exclusive lock on table preventingit from to be updated
From
Bill Moran
Date:
On Mon, 19 Jun 2017 17:33:23 +0000 Dmitry O Litvintsev <litvinse@fnal.gov> wrote: > > The test stand where I was to test schema upgrade is stuck cuz vacuum is blocking. If you're in "panic mode" I would recommend cancelling the existing vacuum, running your upgrades, then immeditely running VACUUM FREEZE ANALYZE on that table to make up for cancelling the autovacuum. Note that the manual VACUUM may take quite a while, so run it in a screen session or something. Additionally, autovacuum is going to try to relaunch that vacuum pretty aggressively, so you might have to cancel it a few times (using pg_terminate_backend()) before your other processes are able to sneak in ahead of it. Once you're out of panic mode you can take some time to breathe and consider your options for reducing the issue in the future. I have to 2nd Alvaro's comments about the cost delay. Personally, I'd recommend setting vacuum_cost_delay to zero, unless your hardware is crap. In my recent experience, allowing vacuum to run full-bore is less intrustive on a busy database with good hardware than forcing it to take it's time. Unfortunately, changing it now isn't going to speed the current vacuum up any. Another comment: schema changes almost always need exclusive locks on tables that they're modifying. As a result, you really need to plan them out a bit. Anything could block a schema update, even a simple SELECT statement; so it's important to check the health of things before starting. While it's not _generally_ a good practice to interrupt autovacuum, it _can_ be done if the schema upgrade is necessary. Keep in mind that it's just going to start back up again, but hopefully your schema update will be done by then and it can do it's work without interfering with things. Another thing you can do is to monitor the transaction ID values (the Nagios check_postgres has a nice mode for monitoring this) and manually launch a VACUUM FREEZE ahead of autovacuum, so that _you_ can pick the time for it to run and not have it happen to crop up at the worst possible time ;) You might also find that things are easier to deal with if you tweak the autovacuum settings on this table to cause it to be vacuumed more frequently. In my experience, more frequent vacuums that do less work each time often lead to happier databases. See ALTER TABLE and the available settings to tweak autovacuum behavior. -- Bill Moran <wmoran@potentialtech.com>
Re: [GENERAL] autovacuum holds exclusive lock on table preventing itfrom to be updated
From
Dmitry O Litvintsev
Date:
yes, we had to restart database 4 days ago (and vacuum has resumed on start).
I checked the log files and discovered that autovacuum on this table takes
pages: 0 removed, 14072307 remain
tuples: 43524292 removed, 395006545 remain
buffer usage: -1493114028 hits, 107664973 misses, 30263658 dirtied
avg read rate: 1.604 MB/s, avg write rate: 0.451 MB/s
system usage: CPU 2055.81s/17710.94u sec elapsed 524356.57 sec
6 days. So it is perpetually being autovacuumed (which I assumed to be a good thing)
Table has 400M entries, 115 GB.
I will try your suggestions in the test environment.
Thank you,
Dmitry
________________________________________
From: Jeff Janes <jeff.janes@gmail.com>
Sent: Monday, June 19, 2017 1:16 PM
To: Dmitry O Litvintsev
Cc: Andreas Kretschmer; pgsql-general@postgresql.org
Subject: Re: [GENERAL] autovacuum holds exclusive lock on table preventing it from to be updated
On Mon, Jun 19, 2017 at 10:33 AM, Dmitry O Litvintsev <litvinse@fnal.gov<mailto:litvinse@fnal.gov>> wrote:
Hi
Since I have posted this nothing really changed. I am starting to panic (mildly).
The source (production) runs :
relname | mode | granted | substr
| query_start | age
----------------------------+--------------------------+---------+----------------------------------------------------------------------+-------------------------------+------------------------
t_inodes_iio_idx | RowExclusiveLock | t | autovacuum: VACUUM ANALYZE public.t_inodes (to
preventwraparound) | 2017-06-15 10:26:18.643209-05 | 4 days 01:58:56.697559
This is close to unreadable. You can use use \x to get output from psql which survives email more readably.
Your first report was 6 days ago. Why is the job only 4 days old? Are you frequently restarting your production
server,so that the vacuum job never gets a chance to finish? If so, that would explain your predicament.
And how big is this table, that it takes at least 4 days to VACUUM?
vacuum_cost_delay = 50ms
That is a lot. The default value for this is 0. The default value for autovacuum_vacuum_cost_delay is 20, which is
usuallytoo high for giant databases.
I think you are changing this in the wrong direction. Rather than increase vacuum_cost_delay, you need to decrease
autovacuum_vacuum_cost_delay,so that you won't keep having problems in the future.
On your test server, change vacuum_cost_delay to zero and then initiate a manual vacuum of the table. It will block on
theautovacuum's lock, so then kill the autovacuum (best to have the manual vacuum queued up first, otherwise it will be
racebetween when you start the manual vacuum, and when the autovacuum automatically restarts, to see who gets the
lock).See how long it takes this unthrottled vacuum to run, and how much effect the IO it causes has on the performance
ofother tasks. If acceptable, repeat this on production (although really, I don't that you have much of a choice on
whetherthe effect it is acceptable or not--it needs to be done.)
Cheers,
Jeff
Re: [GENERAL] autovacuum holds exclusive lock on table preventing itfrom to be updated
From
Scott Marlowe
Date:
On Mon, Jun 19, 2017 at 1:53 PM, Dmitry O Litvintsev <litvinse@fnal.gov> wrote: > yes, we had to restart database 4 days ago (and vacuum has resumed on start). > I checked the log files and discovered that autovacuum on this table takes > > pages: 0 removed, 14072307 remain > tuples: 43524292 removed, 395006545 remain > buffer usage: -1493114028 hits, 107664973 misses, 30263658 dirtied > avg read rate: 1.604 MB/s, avg write rate: 0.451 MB/s > system usage: CPU 2055.81s/17710.94u sec elapsed 524356.57 sec > > 6 days. So it is perpetually being autovacuumed (which I assumed to be a good thing) > > Table has 400M entries, 115 GB. > > I will try your suggestions in the test environment. > > Thank you, > Dmitry Once you get this sorted, look into using the checkpostgresql.pl script and a monitoring solution like zabbix or nagios to monitor things like transactions until wraparound etc so you don't wind up back here again. Best of luck in. Note that if you drop the vacuum delay to 0ms the vacuum will probably complete in a few hours tops.