From: Chirag Dave <cdave@ca.afilias.info>
To: pgsql-admin@postgresql.org
Subject: Postgres Stats after Crash Recovery
Date: Wed, 24 Sep 2008 15:29:59 -0400
Message-ID: <f1d4f3170809241229t50465cddx2f8f44c2507df935@mail.gmail.com> (raw)
Testing AutoVac on 8.3 , i came across the problem of loosing stats data,
which was discussed in my last post
http://archives.postgresql.org/pgsql-general/2008-08/msg00198.php
that problem was recognized that doing hard stop, server will throw away the
stats while going through crash recovery.
Problem i see is after crash recovery , we have to manually analyze database
in order for autovac to work but it not working as expected.
Here is test case:
foo=# SELECT version();
version
------------------------------------------------------------------------------------------------
PostgreSQL 8.3.3 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 4.1.2
(Ubuntu 4.1.2-0ubuntu4)
(1 row)
foo=# SELECT * from pg_stat_user_tables where relname='accounts';
-[ RECORD 1 ]----+------------------------------
relid | 57350
schemaname | public
relname | accounts
seq_scan | 1
seq_tup_read | 1000000
idx_scan | 0
idx_tup_fetch | 0
n_tup_ins | 1000000
n_tup_upd | 0
n_tup_del | 0
n_tup_hot_upd | 0
n_live_tup | 1000000
n_dead_tup | 0
last_vacuum | 2008-09-24 15:04:35.384012-04
last_autovacuum |
last_analyze | 2008-09-24 15:04:35.384012-04
last_autoanalyze |
Next i will stop DB immediate and expect to loose stats as normal behavior.
pg_ctl -m immediate -D /opt/rg/foo/pgsql83 stop
waiting for server to shut down...LOG: received immediate shutdown request
done
server stopped
After stating the DB, as expected:
foo=# SELECT * from pg_stat_user_tables where relname='accounts';
-[ RECORD 1 ]----+---------
relid | 57350
schemaname | public
relname | accounts
seq_scan | 0
seq_tup_read | 0
idx_scan | 0
idx_tup_fetch | 0
n_tup_ins | 0
n_tup_upd | 0
n_tup_del | 0
n_tup_hot_upd | 0
n_live_tup | 0
n_dead_tup | 0
last_vacuum |
last_autovacuum |
last_analyze |
last_autoanalyze |
Next step is to manually analyse to collects the stats again:
foo=# ANALYZE ;
ANALYZE
foo=# SELECT * from pg_stat_user_tables where relname='accounts';
-[ RECORD 1 ]----+---------
relid | 57350
schemaname | public
relname | accounts
seq_scan | 0
seq_tup_read | 0
idx_scan | 0
idx_tup_fetch | 0
n_tup_ins | 0
n_tup_upd | 0
n_tup_del | 0
n_tup_hot_upd | 0
n_live_tup | 0
n_dead_tup | 0
last_vacuum |
last_autovacuum |
last_analyze |
last_autoanalyze |
note: After ANALYSE, ststs were not updated.
Running ANALYSE, second time seems to does the trick.
foo=# ANALYZE ;
ANALYZE
foo=# SELECT * from pg_stat_user_tables where relname='accounts';
-[ RECORD 1 ]----+------------------------------
relid | 57350
schemaname | public
relname | accounts
seq_scan | 0
seq_tup_read | 0
idx_scan | 0
idx_tup_fetch | 0
n_tup_ins | 0
n_tup_upd | 0
n_tup_del | 0
n_tup_hot_upd | 0
n_live_tup | 1000062
n_dead_tup | 0
last_vacuum |
last_autovacuum |
last_analyze | 2008-09-24 15:13:13.423424-04
last_autoanalyze |
So question i have is, is this normal operation,why we need to analyze twice
to updates the stats ? if table/tables are candidate for vacuuming after
crash recovery will never get auto-vac unless you do 'ANALYZE' twice.
Thanks in advance,
Chirag Dave
DBA
Afilias
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To: pgsql-admin@postgresql.org
Cc: cdave@ca.afilias.info
Subject: Re: Postgres Stats after Crash Recovery
In-Reply-To: <f1d4f3170809241229t50465cddx2f8f44c2507df935@mail.gmail.com>
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