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Re: Hash join on int takes 8..114 seconds

From: "Andrus" <kobruleht2(at)hot(dot)ee>
To: "Richard Huxton" <dev(at)archonet(dot)com>
Cc: "PFC" <lists(at)peufeu(dot)com>,<pgsql-performance(at)postgresql(dot)org>
Subject: Re: Hash join on int takes 8..114 seconds
Date: 2008-11-21 17:51:01
Message-ID: 8A78204AA6D44C04B053E6412B244E13@andrusnotebook (view raw, whole thread or download thread mbox)
Lists: pgsql-performance

Thank you.

> Try "SELECT count(*) FROM pg_shdepend".

This query returns 3625  and takes 35 seconds to run.

> If it's not a million rows, then the table is bloated. Try (as postgres
> or some other db superuser) "vacuum full pg_shdepend" and a "reindex
> pg_shdepend".

vacuum full verbose pg_shdepend
INFO:  vacuuming "pg_catalog.pg_shdepend"
INFO:  "pg_shdepend": found 16103561 removable, 3629 nonremovable row 
versions in 131425 pages
DETAIL:  0 dead row versions cannot be removed yet.
Nonremovable row versions range from 49 to 49 bytes long.
There were 0 unused item pointers.
Total free space (including removable row versions) is 1009387632 bytes.
131363 pages are or will become empty, including 0 at the end of the table.
131425 pages containing 1009387632 free bytes are potential move 
CPU 2.12s/1.69u sec elapsed 52.66 sec.
INFO:  index "pg_shdepend_depender_index" now contains 3629 row versions in 
101794 pages
DETAIL:  16103561 index row versions were removed.
101311 index pages have been deleted, 20000 are currently reusable.
CPU 20.12s/14.52u sec elapsed 220.66 sec.

After 400 seconds of run I got phone calls that server does not respond to 
other clients. So I was forced to cancel "vacuum full verbose pg_shdepend
" command.

How to run it so that other users can use database at same time ?

> If it is a million rows, you'll need to find out why. Do you have a lot
> of temporary tables that aren't being dropped or something similar?

Application creates temporary tables in many places. Every sales operation 
probably creates some temporary tables.
Should I change something in configuration or change application (Only 
single POS application which is used to access this db) or is only solution 
to manully run

vacuum full pg_shdepend
reindex pg_shdepend

periodically ?
How to vacuum full pg_shdepend automatically so that other users can work at 
same time ?

Hopefully this table size does not affect to query speed.


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