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List:       postgresql-general
Subject:    Re: postgres stats on the new primary
From:       Ian Barwick <ian.barwick () 2ndquadrant ! com>
Date:       2020-07-28 1:53:49
Message-ID: 94734afa-1110-900e-a8a9-51a1219e14a8 () 2ndquadrant ! com
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On 2020/07/28 9:08, Ayub M wrote:
 > I have a RDS PostgreSQL v11.6 with primary and standby. On the primary, vacuum/analyze
 > were running and  pg_stat_all_tables's last_vacuum/analyze/autovacuum/autoanalyze
 > were having values when vacuum/analyze were run.
 >
 > 1. Switchover to Standby happened, now when I see pg_stat_all_tables (on the active
 > primary which was standby earlier), the last vacuum/analyze columns are all nulls.
 > Would primary-standby replication not replicate system tables? Is this how it behaves?

The information shown by the various pg_stat_* views is specific to the local
server, and is *not* replicated. In most cases that wouldn't even make
sense. The information is collated by the statistics collector [1] and is stored
in memory and/or files in the data directory, not as a system table.

[1] https://www.postgresql.org/docs/current/monitoring-stats.html

 > 2. On the new primary, would the table have stats on them? (I do see pg_stats
 > entries for the tables on new standby), are they reliable or do I need to gather
 > stats and run vacuum after failover/switchover to standby?

The statistics about the *contents* of the database, as shown by pg_stats, are of
course replicated and will be reliable. More precisely they'll be as up-to-date
as the last vacuum/analyze on the former primary, just you won't see the
information about when that was.


Regards

Ian Barwick

-- 
Ian Barwick                   https://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services


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