Skip site navigation (1) Skip section navigation (2)

Re: how to fix problem then when two queries run at the same time, it takes longer to complete then if run in sequence

From: Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>
To: Miernik <public(at)public(dot)miernik(dot)name>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: how to fix problem then when two queries run at the same time, it takes longer to complete then if run in sequence
Date: 2008-07-31 10:24:32
Message-ID: 489192E0.9010309@postnewspapers.com.au (view raw or flat)
Thread:
Lists: pgsql-performance
Miernik wrote:

> BTW, doesn't there exist any tool does what "psql -c" does, but is
> written in plain C, not perl? I was looking for such psql replacement,
> but couldn't find any.

As others have noted, psql is written in C, and you're using a wrapper.

Assuming your're on Debian or similar you should be able to invoke the
real psql with:

/usr/lib/postgresql/8.3/bin/psql

psql is a C executable that uses libpq directly, and is really rather
low-overhead and fast.

As for how to issue multiple commands in one statement in a shell
script: one way is to use a here document instead of "-c". Eg:


psql <<__END__
UPDATE blah SET thingy = 7 WHERE otherthingy = 4;
DELETE FROM sometable WHERE criterion = -1;
__END__

You can of course wrap statements in explicit transaction BEGIN/COMMIT,
etc, as appropriate.

As you start doing more complex things, and especially once you start
wanting to have both good performance *and* good error handling, you'll
want to move away from sql scripts with psql and toward using perl,
python, or similar so you can use their native interfaces to libpq.

--
Craig Ringer

In response to

pgsql-performance by date

Next:From: Steve CrawfordDate: 2008-07-31 15:30:35
Subject: Re: how to fix problem then when two queries run at the same time, it takes longer to complete then if run in sequence
Previous:From: Theo KramerDate: 2008-07-31 09:52:12
Subject: Re: how to fix problem then when two queries run at the same time, it takes longer to complete then if run in sequence

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group