Re: improve select performance... - Mailing list pgsql-admin

Can you post the actual queries and the full EXPLAIN ANALYZE for the
queries?

Are you running 64bit Debian and PostgreSQL?

Cheers,
~p

-----Original Message-----
From: pgsql-admin-owner@postgresql.org
[mailto:pgsql-admin-owner@postgresql.org] On Behalf Of Steve Holdoway
Sent: Wednesday, 16 May 2007 09:08
To: pgsql-admin@postgresql.org
Subject: [ADMIN] improve select performance...

Can anyone out there help me, I'm having a bit of a problem trying to
improve the performance of a php script that does a data load?

At the moment, the script checks a database to see if the entry is present,
and, if not, it adds it. The table has about 400,000 rows, and I'm checking
a bulk load of about 50,000 entries. The table is defined as follows (not my
design!):

Welcome to psql 8.2.4, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help with psql commands
       \g or terminate with semicolon to execute query
       \q to quit

db=> \d badurls
                     Table "public.badurls"
   Column    |            Type             |     Modifiers
-------------+-----------------------------+--------------------
 url         | character varying           | not null
 ip          | character(20)               |
 dateadded   | timestamp without time zone | not null
 type        | character(1)                |
 publishdate | timestamp without time zone |
 status      | integer                     | not null default 1
 version     | integer                     | default 0
 edited      | integer                     | default 0
 category    | character(4)[]              |
Indexes:
    "idxbadurls_url" hash (url)
    "idxbadurls_version" btree (version)


and I'm accessing the url column. (I've tried a btree index as well... not
much difference)

In an attempt to improve the performance, I'm getting a list of data that's
already there in a single hit, and not attempting to insert them ( I'm still
checking the rest first, just in case... ).

So, I'm trying to run a select url from badurls where url in ( .... ) to get
this list. However, this is also desperately slow...

1000 in the list: 14 sec
5000 in the list: 2:40
10000 in the list: 5:50

( run from a client machine over a 100mbit lan ).

Anyway, that's enough to prove to me that I need to rejig stuff to get this
to work!!!

Server's a dual xeon machine, with hardware raid, and running debian. It's
got 4GB of memory, 1GB is currently not even used for io buffers.

The postgres instance is configured as standard, except for increasing the
shared_buffers to 200MB.

Explain plan for about 50 entries in the 'in' clause returns

Bitmap Heap Scan on badurls  (cost=4531.22..15748.67 rows=60462 width=32)
   Recheck Cond: ((url)::text = ANY (('{.....}'::character
varying[])::text[]))
   ->  Bitmap Index Scan on idxbadurls_url  (cost=0.00..4516.10 rows=60462
width=0)
         Index Cond: ((url)::text = ANY (('{.....}'::character
varying[])::text[]))
(4 rows)


Can anyone suggest what I should be reconfiguring???

Cheers,


Steve

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