Re: pg_toast table growth out of control - Mailing list pgsql-general

From Jan Wieck
Subject Re: pg_toast table growth out of control
Date
Msg-id 200203112304.g2BN4NN28909@saturn.janwieck.net
Whole thread Raw
In response to Re: pg_toast table growth out of control  ("Jeffrey W. Baker" <jwb@saturn5.com>)
Responses Re: pg_toast table growth out of control  ("Jeffrey W. Baker" <jwb@saturn5.com>)
List pgsql-general
Jeffrey W. Baker wrote:
> On Mon, 2002-03-11 at 14:07, Jan Wieck wrote:
> >     You  actually  did a VACUUM FULL and it didn't shrink? In 7.2
> >     no table does shrink on a normal VACUUM. So if you don't  run
> >     VACUUM FULL, it cannot!
>
> You still don't understand my problem.  I insert into this database at
> the rate of 1000 rows per hour.  Every hour, I delete the rows that are
> more than 1 day old and vacuum.  Thus, the maximum size of the table
> should be 24 * 1000 = 24000 rows and the file size should be stable.
>
> HOWEVER
>
> The actual observed behavior is that the file simply grows constantly.
> Forever.  No stability.  Period.  Despite the fact that select count(*)
> from table == a constant.

    Get the name of the toast table with

        SELECT T.relname FROM pg_class T, pg_class R
            WHERE R.relname = '<your main tables name>'
            AND   R.reltoastrelid = T.oid;

    Now query that toast table with:

        SELECT sum(length(chunk_data)) FROM pg_toast_????????;

    What is the length sum and how big is the real file?

    Another question, do you frequently restart the postmaster? I
    don't know for sure, but maybe a restart  of  the  postmaster
    will  cause  you  to loose the freespace map for the relation
    and therefore all new tuples go allways at the end, not  into
    some free'd space.

    How big is the freespace map anyway, could this be an example
    for that this table needs to be vacuumed even more often than
    once per hour, Tom?


Jan

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