From: Gnanakumar <gnanam@zoniac.com>
To: 'Alvaro Herrera' <alvherre@commandprompt.com>
Cc: pgsql-admin@postgresql.org
Subject: Re: Autovacuum daemon functionality questions
Date: Fri, 9 Apr 2010 13:07:20 +0530
Message-ID: <001701cad7b7$7f1e2730$7d5a7590$@com> (raw)
In-Reply-To: <20100408145328.GB4126@alvh.no-ip.org>
References: <00c001cad728$22f92f20$68eb8d60$@com>
<20100408145328.GB4126@alvh.no-ip.org>
>> 1. Why need to have 2 parameters (base threshold and scale factor) to
define
>> the threshold value, when either one of the parameter is more than enough
to
>> define the threshold value. Can you explain the significance of having
both
>> parameters. What is the real-time advantage of this?
>real-time advantage? They are just the two factors in a linear
>equation.
>> 2. Documentation says ".... If the number of obsolete tuples since the
last
>> VACUUM exceeds the "vacuum threshold", the table is vacuumed ...".
>> I also know about this table "pg_stat_user_tables" which has columns
>> n_tup_ins, n_tup_upd, n_tup_del, last_autovaccum and last_autoanalyze.
>> Since INSERT, UPDATE and DELETE count gets incremented everytime and do
not
>> reset after running autovacuum/autoanalyze, how does autovacuum
identifies
>> obsolete tuples since last VACUUM from this entries.
>There are two separate counters for live and dead tuples, IIRC (though
>they may not be exposed in the pg_stat views)
I've a stop/start of PostgreSQL service on a daily basis. Since these 2
counters are not stored/saved in tables and not available in pg_stat views
also, will these values be persisted/retained even after stop/start/restart?
>There are two separate counters for live and dead tuples
As per documentation, live tuples can always be obtained from
pg_class.reltuples. So, the question/answer here again would be to have
only counter on dead tuples since last VACUUM. Is my understanding right?
Is there some other/alternative way where I can check obsolete tuples at any
time since last VACUUM?
>> 3. Is there a way to see autovacuum daemon log entries?
>Not in 8.2.
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-admin@postgresql.org
Cc: gnanam@zoniac.com, alvherre@commandprompt.com
Subject: Re: Autovacuum daemon functionality questions
In-Reply-To: <001701cad7b7$7f1e2730$7d5a7590$@com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox