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Re: [PATCHES] Implemented current_query

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Neil Conway <neilc(at)samurai(dot)com>
Cc: Tomas Doran <bobtfish(at)bobtfish(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: [PATCHES] Implemented current_query
Date: 2008-03-28 17:23:09
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Lists: pgsql-hackerspgsql-patches
Neil Conway wrote:
> On Mon, 2007-07-05 at 19:48 +0100, Tomas Doran wrote:
> > As suggested in the TODO list (and as I need the functionality  
> > myself), I have implemented the current_query interface to  
> > debug_query_string.

It actually has been removed from the TODO list since you saw it last.

> Comments:
> * AFAIK debug_query_string() still does the wrong thing when the user
> submits multiple queries in a single protocol message (separated by
> semi-colons). Not sure there's a way to fix that that is both easy and
> efficient, though...

The problem with the last bullet is pretty serious.  It can be
illustrated with psql:

	$ psql -c 'set log_statement="all";select 1;select 2;' test

Server log shows:

	STATEMENT:  set log_statement=all;select 1;select 2;

Obviously this is what current_query() would return if we commit this
patch, and it probably isn't 100% accurate.  I see dblink exposes this:

    Returns the currently executing interactive command string of the
    local database session, or NULL if it can't be determined.  Note
    that this function is not really related to <filename>dblink</>'s
    other functionality.  It is provided since it is sometimes useful
    in generating queries to be forwarded to remote databases.

but making it more widely available with a possible inaccurate result is
a problem.  We can't think of anyway to fix this cleanly --- it would
require a separate parser pass to split queries by semicolons (which
psql does by default in interactive mode).  Right now the parser does
the splitting as part of its normal single-parse operation and just
creates parse trees that don't have string representations.

Perhaps we could name it received_query() to indicate it is what the
backend received and it not necessarily the _current_ query.

  Bruce Momjian  <bruce(at)momjian(dot)us>

  + If your life is a hard drive, Christ can be your backup. +

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