Message-Id: <200212280933.gBS9XjgJ070854@aaz.links.ru>
Subject: Re: libpq and multiple selects in a single query
In-Reply-To: <E4A80FA6-1A38-11D7-96DD-000393460410@mac.com>
To: Tim Hart <tjhart@mac.com>
Date: Sat, 28 Dec 2002 12:33:45 +0300 (MSK)
From: "."@babolo.ru
Cc: pgsql-interfaces@postgresql.org
MIME-Version: 1.0

> I was musing a bit today, so don't take this to seriously...
> 
> Would it be worth the effort to add to and/or modify the libpq API so 
> that multiple selects could be sent to the server in a single request 
> and response?
Multiple selects can be sent to the server now.
But as far as I unerstand only last result can
be fetched:
0>pgoblin -s
SELECT date(now());SELECT now()
2002-12-28 12:16:49.321118+03

pgoblin is my direct interface from command line to libpq
with some scripting enhancement

>               Obviously, this is trivial from the command line...
> select * from foo; select * from bar;
You mean "from psql"?
psql is complex tool with its own parser and use
libpq to talk to server

> But - at least as far as I understand the libpq API - only one select 
> can be issued using PQexec.
> 
> In many of the apps I develop, I find that the majority of the time I 
> have to go to the database for a select, I have to select from several 
> tables. I haven't done any benchmarking, but given the rule-of-thumb 
> that inter-process communication incurs high overhead, I decided that 
Usually it is not true - compared to postmaster's
cost for every query.
...or may be... Do you issue PQsetdbLogin for every PQexec?

> being able to issue several statements in one call might be worth 
> investigating. Given the holiday season though, I haven't actually done 
> much work to see if PQexec actually does support this. I'd be surprised 
> if a client-server or n-tier app wouldn't benefit from this 
> functionality.

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