From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tony Cebzanov <tonyceb@andrew.cmu.edu>
Cc: Richard Huxton <dev@archonet.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Avoiding cycles in a directed graph
Date: Tue, 16 Mar 2010 17:09:12 -0400
Message-ID: <14550.1268773752@sss.pgh.pa.us> (raw)
In-Reply-To: <4B9FEEE8.1060404@andrew.cmu.edu>
References: <4B9FDFDE.5030005@andrew.cmu.edu>
<4B9FE752.4080709@archonet.com>
<14113.1268771643@sss.pgh.pa.us>
<4B9FEEE8.1060404@andrew.cmu.edu>
Tony Cebzanov <tonyceb@andrew.cmu.edu> writes:
> I'm okay with running the big, fat WITH RECURSIVE query in my insert
> trigger if I have to -- it won't be great for performance, but I don't
> expect this to be a frequent operation, so I'll accept the performance
> hit if it works.
> Unfortunately I can't even get that working. Here's the (not at all
> functional) trigger I've got right now, which only detects the cycle
> *after* it's been inserted, which is of no help at all. Any way I can
> modify this to do the right thing?
Run it in an AFTER trigger?
If you don't expect this to be common, maybe you could fix the
concurrency issue by taking a table-wide lock that locks out
other writers.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, tonyceb@andrew.cmu.edu, dev@archonet.com
Subject: Re: Avoiding cycles in a directed graph
In-Reply-To: <14550.1268773752@sss.pgh.pa.us>
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