RE: Are my autovacuum settings too aggressive for this table? - Mailing list pgsql-general

Michael Lewis <mlewis@entrata.com> writes:
>My thinking is opposite from what you have. I consider it important to very aggressive on autovacuum because it only
everdoes the required amount of >work. If a tiny amount of work is needed, it does only that and is done. Assuming it
doesn'tcause I/O concerns, do it as often as possible to minimize the> growth of bloat and maximize the reuse of the
spacealready allocated to that relation. 

Excellent, I am not seeing any I/O concerns, and it seems to be keeping up now, so I will keep this setting unless
someoneelse points out another suggestion. 

>On the subject of analyze, the statistics are unlikely to be impacted significantly by inserting about 24k rows to a
tablewith almost 20 million already. >With default_statistics_target at 100, what are the chances those new rows will
evenbe included in the sample? I don't know the math, but given each >run of analyze does the same ALL the work each
andevery time it runs, it seems prudent to do them a little less often than autovacuum anyway. >Regardless though,
autoanalyzeis a small amount of work that it does each time. 

I agree, this is excellent advice, I overlooked the fact that this is a sample and the new rows may not even be
includedin this sample.  I will adjust accordingly. 


-----Original Message-----
From: Jason Ralph <jralph@affinitysolutions.com>
Sent: Friday, November 1, 2019 2:59 PM
To: pgsql-general@lists.postgresql.org
Cc: Jason Ralph <jralph@affinitysolutions.com>
Subject: Are my autovacuum settings too aggressive for this table?

Hello list,

DB1=# select version();
-[ RECORD 1 ]----------------------------------------------------------------------------------------------------
version | PostgreSQL 11.5 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-23), 64-bit


I am sure this question has come up before, I have scoured the documentation and I think I have a good grasp on the
autovacuum. I wanted to ask the team if my settings for this particular table are too aggressive, I have the following
setwhich is producing a vacuum analyze multiple times a day. 

I think the defaults out of the box were not aggressive enough, so I went with the following on the global level, I
willpossibly move to table level if needed.  I tried to show the stats below of a 10 minute interval during peak time.
Anypush in the right direction is appreciated, I want my tables analyzed and vacuumed but do not want to over do it.
Therest of the autovacuum settings are default. 

I know the stats are estimates so here is my calculations.

Live tuples = 19,766,480
Analyze scale factor = 0.001
Analyze thresh = 5000
Thresh + live_tuples * factor = 24,766

So an autovacuum analyze should trigger around 24K tuples modified, is this to little or too much? Same goes for
autvacuumvacuum, is it too aggressive? 

#------------------------------------------------------------------------------
# AUTOVACUUM
#------------------------------------------------------------------------------
autovacuum_naptime = 1h
autovacuum_vacuum_threshold = 10000
autovacuum_analyze_threshold = 5000
autovacuum_vacuum_scale_factor = 0.002
autovacuum_analyze_scale_factor = 0.001




DB1=# \x
Expanded display is on.
DB1=# select now();
-[ RECORD 1 ]----------------------
now | 2019-11-01 14:35:51.893328-04

DB1=# select * from pg_stat_user_tables where relname = 'members'; -[ RECORD 1 ]-------+------------------------------
relid               | 18583
schemaname          | public
relname             | members
seq_scan            | 129
seq_tup_read        | 2036932707
idx_scan            | 546161742
idx_tup_fetch       | 1670607103
n_tup_ins           | 46742
n_tup_upd           | 35704112
n_tup_del           | 0
n_tup_hot_upd       | 31106485
n_live_tup          | 19766480
n_dead_tup          | 1844251
n_mod_since_analyze | 15191
last_vacuum         | 2019-10-13 15:42:06.043385-04
last_autovacuum     | 2019-11-01 12:24:45.575283-04
last_analyze        | 2019-10-13 15:42:17.370086-04
last_autoanalyze    | 2019-11-01 12:25:17.181133-04
vacuum_count        | 2
autovacuum_count    | 15
analyze_count       | 2
autoanalyze_count   | 17

DB1=# select now();
-[ RECORD 1 ]----------------------
now | 2019-11-01 14:45:10.845269-04

DB1=# select * from pg_stat_user_tables where relname = 'members'; -[ RECORD 1 ]-------+------------------------------
relid               | 18583
schemaname          | public
relname             | members
seq_scan            | 129
seq_tup_read        | 2036932707
idx_scan            | 546171120
idx_tup_fetch       | 1670615505
n_tup_ins           | 46742
n_tup_upd           | 35705068
n_tup_del           | 0
n_tup_hot_upd       | 31107303
n_live_tup          | 19766480
n_dead_tup          | 1844881
n_mod_since_analyze | 16147
last_vacuum         | 2019-10-13 15:42:06.043385-04
last_autovacuum     | 2019-11-01 12:24:45.575283-04
last_analyze        | 2019-10-13 15:42:17.370086-04
last_autoanalyze    | 2019-11-01 12:25:17.181133-04
vacuum_count        | 2
autovacuum_count    | 15
analyze_count       | 2
autoanalyze_count   | 17

Thanks for your time,
Jason Ralph

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