Message-ID: <489192E0.9010309@postnewspapers.com.au>
Date: Thu, 31 Jul 2008 18:24:32 +0800
From: Craig Ringer <craig@postnewspapers.com.au>
User-Agent: Icedove 1.5.0.14eol (X11/20080509)
MIME-Version: 1.0
To: Miernik <public@public.miernik.name>
Cc: pgsql-performance@postgresql.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
References: <20080723152112.30A4.0.NOFFLE@turbacz.local>
	<dcc563d10807231025s617c6b16neb93c6348a658cdb@mail.gmail.com>
	<20080723203203.31C4.0.NOFFLE@turbacz.local>
	<488840D3.2090808@archonet.com>
	<20080731061522.54FE.0.NOFFLE@turbacz.local>
	<48916B6A.4070203@archonet.com>
	<20080731082930.553C.0.NOFFLE@turbacz.local>
In-Reply-To: <20080731082930.553C.0.NOFFLE@turbacz.local>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

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