Re: autovacuum was not vacuuming

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On May 27, 2015, at 2:00 PM, Alvaro Herrera <alvherre@xxxxxxxxxxxxxxx> wrote:

> Charles Sprickman wrote:
>> On May 27, 2015, at 1:37 PM, Jorge Torralba <jorge.torralba@xxxxxxxxx> wrote:
>> 
>>> run this for validation
>>> 
>>> select relname, last_autovacuum from pg_stat_user_tables order by last_autovacuum;
>> 
>> Hi - thanks, I’d run some similar query before to see what wasn’t being vacuumed.
>> 
>> While some tables seem to be now, here’s an example of an active db that’s still got some blanks in the last_autovacuum column:
> 
> Does your system crash frequently?  autovacuum would not process files
> unless they appear to cross the threshold values; and the statistics are
> reset whenever there's a crash recovery.  

No frequent crashes.  Not any that I know of even since moving to
this server (up 1046 days).  So thats one thing to rule out.  I also
know that no one has manually reset any of the stats counters.

> Perhaps those tables don't
> have enough recent activity.  I see your oldest autovac dates are
> 2014-07 so perhaps you had crashes sometime before that.

This is starting to make sense.

On the same database, this data is kind of interesting:

       relname       | n_tup_ins | n_tup_upd | n_tup_del |        last_autovacuum        | autovacuum_count
---------------------+-----------+-----------+-----------+-------------------------------+------------------
 optin               |   7252274 |         0 |   1975631 | 2014-07-21 06:31:47.66319-04  |                3
 log                 |  43045279 |         0 |  31641637 | 2014-10-18 04:55:22.227628-04 |                8
 complaint           |   3002663 |      6154 |   3002973 | 2014-10-18 10:43:18.224247-04 |               31
 arch_subscriber     |   8472659 |   8184029 |     96798 | 2014-11-19 08:27:32.895688-05 |                2
 subscriber          |  13625052 |  28592779 |   8473154 | 2014-12-05 10:12:48.340305-05 |               14
 transactions        |   2514676 |      5182 |    257117 | 2015-02-18 12:47:42.406487-05 |                3
 post                |     32521 |     50722 |      1557 | 2015-05-23 01:46:47.039179-04 |                1
 post_actions        |  98395891 |     43836 |  44881522 | 2015-05-26 10:03:43.259077-04 |                3
 bounce              |    631024 |        81 |    595087 | 2015-05-26 10:29:34.888937-04 |               13
 bounce_reason       |   7961281 |     32736 |   7953428 | 2015-05-26 10:29:34.918845-04 |                6
 list_sub            |  14562995 |  69515258 |   9009496 | 2015-05-28 15:58:13.754569-04 |               30
 post_job            |      8127 |     15908 |      8070 | 2015-05-28 21:52:54.923614-04 |              263
 list_data           |      7350 |    756705 |      6063 | 2015-05-29 12:34:42.323142-04 |              425
 post_stats          |     90155 |  40750025 |       108 | 2015-05-29 13:14:43.307775-04 |              569
 limit_tracking      |     30248 |  12689580 |     30192 | 2015-05-29 13:54:42.06234-04  |            50780
 email               |         0 |         0 |         0 |                               |                0
 sending_rule_fields |         0 |         0 |         0 |                               |                0
 sending_rule_files  |         0 |         0 |         0 |                               |                0
 post_threads        |         0 |         0 |         0 |                               |                0
 forwards            |         0 |         0 |         0 |                               |                0
 list                |         9 |        28 |         7 |                               |                0
 sub_active          |    840019 |         0 |         0 |                               |                0
 subscriber_db_field |         0 |         0 |         0 |                               |                0
 slice_fields        |         0 |         0 |         0 |                               |                0
 sending_rule_esps   |         0 |         0 |         0 |                               |                0
 client              |         1 |         0 |         0 |                               |                0
 slices              |         0 |         0 |         0 |                               |                0
 fields              |        11 |         0 |         0 |                               |                0
 arch_list_sub       |   8909636 |         0 |    101140 |                               |                0
 sending_rules       |         0 |         0 |         0 |                               |                0
 subscriber_db_query |         0 |         0 |         0 |                               |                0
 engagement          |         0 |         0 |         0 |                               |                0
 reject_rule         |       608 |         0 |         0 |                               |                0
 list_criterion      |         0 |         0 |         0 |                               |                0
 repltest            |         0 |         0 |         0 |                               |                0
 post_attachment     |         1 |         0 |         0 |                               |                0
 filters             |         0 |         0 |         0 |                               |                0
 messages            |         0 |         0 |         0 |                               |                0
 post_domain         |    262398 |      1177 |       290 |                               |                0
 track_url           |       786 |      1394 |         1 |                               |                0
 subscriber_data     |         0 |         0 |         0 |                               |                0
 message_attachments |         0 |         0 |         0 |                               |                0
 migrations          |        11 |         0 |         0 |                               |                0
 subscriptions       |   8606373 |    463446 |         0 |                               |                0
 mailer              |         0 |         0 |         0 |                               |                0
 subscriber_db_file  |         0 |         0 |         0 |                               |                0
 track_hit           |  29733544 |     86038 |   6383080 |                               |                0
 engagement_rules    |         0 |         0 |         0 |                               |                0
(48 rows)

Of all the tables that have NOT been autovacuumed, only a handful
have any real write activity.  And on those I cant really get any
data as to WHEN the last activity was (unless I reset stats and
wait) although looking a bit closer I see some timestamped columns
and none of these tables have been touched in years.  Good, I think.

Should I be worried about limit_tracking which has been vacuumed
about 50,000 times in the last few days?  :) That seems a little
extreme.

Now if we assume the tables that werent vacuumed are not seeing any
new activity, my next problem is how to satisfy my nagios
check_postgres checks that look for tables that have not been
vacuumed in X days.

> How many workers are currently processing tables?  (See
> pg_stat_activity)  The more workers there are, the slower they become.

By workers, I assume you just mean pg processes?  It varies, but
anywhere between a few dozen and a hundred.

> Perhaps they are all busy processing large tables and they never finish
> because of the vacuum_delay.  On the other hand, naptime=40min means
> that from one worker start to the next one there's a 40min wait, which
> seems a bit too long.  Normally the default of 1min is appropriate; why
> did you change that?

I think because I dont fully grasp how all these variables interact.
IIRC, when I set this it had something to do with compensating for
the number of databases and the number of workers.

Im looking at pgbadger’s analysis of vacuums and I think Im mostly OK
with whats happening.

Im still stumped on why changes from defaults were necessary to get
autovacuum to kick in though

Thanks,

Charles

> 
> -- 
> Álvaro Herrera                http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
> 
> 
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