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Date: Thu, 15 May 2003 14:06:36 -0500
From: Matt Mello <alien@spaceship.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-sql@postgresql.org
Subject: Re: "deadlock detected" documentation
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Okay, so one last question on this...

If I do the following, assuming I haven't applied the patch, will it 
still result in a deadlock (in other words, does this only happen with 
multi-record updates, or can it happen with independent single-record 
updates inside transactions)?

THREAD1:                                                THREAD2:

BEGIN;
update txn set ... where txn.terminalid = 1;

                                                           BEGIN;
                     update txn set ... where txn.terminalid = 2;

(I anticipate the next statement will give me a deadlock.)

update txn set ... where txn.terminalid = 2;

                     update txn set ... where txn.terminalid = 1;
COMMIT;

                                                          COMMIT;

Thanks, again!


Tom Lane wrote:
> Matt Mello <alien@spaceship.com> writes:
> 
>>I see.  One item I forgot to mention ...  Both update statements have a 
>>where clause containing txn.terminalid=38.  Txn.terminalid is a foreign 
>>key column in that table (txn.terminalid->terminal.terminalid).  Could 
>>this be the source of the trouble?
> 
> 
> Not per se.  The problem depends on which rows get updated and in what
> sequence --- the contents of the WHERE clause aren't the issue, except
> insofar as they determine the set of rows to be updated.
> 
> 			regards, tom lane
> 
> 

-- 
Matt Mello
512-350-6900