Re: Tracking down deadlocks

So is everybody simply accepting the chance of deadlocks, thanks to
their foreign keys? Given what I know about why this problem exists, it
doesn't seem to have an easy solution.... but from my naive perspective
it seems like something that we shouldn't have to just live with,
either.

On Jun 16, 2004, at 10:50 AM, Joshua D. Drake wrote:

> Hello,
>
> Deferred checks can greatly reduce the deadlock chance because of the
> timing of the foreign key check. I won't say it can eliminate them,
> and I don't think anyone here would suggest that you don't use Foreign
> keys.
>
> Sincerely,
>
> Joshua D. Drake
>
> Ben wrote:
>> Thanks for the quick reply (and summary!).
>> According to the messages I've found on the list, basically the
>> answer seems to be, "don't do this." On the other hand, pretty much
>> every message on the subject is pre-7.4. There is some mention of
>> using deferred foreign keys to reduce the chance for a deadlock, but
>> nothing says doing that actually eliminates the chance.
>> Is this just a known limitation? In this particular instance, I
>> probably could get rid of my foreign keys and if things go bad it
>> wouldn't hurt anything.... but I make heavy use of foreign keys
>> throughout the rest of my schema, which are useful for the programs
>> that aren't doing data mining. I wouldn't want to get rid of those
>> foreign keys.
>> On Jun 16, 2004, at 8:54 AM, Csaba Nagy wrote:
>>> Hi Ben,
>>>
>>> Check this mailing list for "foreign keys" and "deadlock".
>>> Short info:
>>> Postgres exclusively locks the referenced records of a foreign key
>>> relationship when the child record is updated, so multiple runs (in
>>> different transactions) of one insert query could cause deadlock if
>>> they
>>> update rows which reference the same parent keys in reverse order.
>>> Check your foreign keys...
>>>
>>> HTH,
>>> Csaba.
>>>
>>> On Wed, 2004-06-16 at 17:33, Ben wrote:
>>>
>>>> I'm doing a bunch of data mining against a postgres database and
>>>> have
>>>> run into an interesting problem with deadlocks. The problem is,
>>>> postgres is detecting them and then wacking the offending process,
>>>> and
>>>> I can't figure out what's causing them. I have a ton of select
>>>> queries
>>>> (but none for update), and then a single query to insert into a
>>>> table.
>>>> Nothing selects from that table. So where could the deadlock be?
>>>>
>>>> pg_stat_activity has a column named current_query, which would seem
>>>> useful in tracking this down, but it's not being populated.
>>>>
>>>> Oh, I'm running 7.4.2.
>>>>
>>>>
>>>> ---------------------------(end of
>>>> broadcast)---------------------------
>>>> TIP 5: Have you checked our extensive FAQ?
>>>>
>>>>                http://www.postgresql.org/docs/faqs/FAQ.html
>>>
>>>
>> ---------------------------(end of
>> broadcast)---------------------------
>> TIP 9: the planner will ignore your desire to choose an index scan if
>> your
>>      joining column's datatypes do not match
>
>
> --
> Command Prompt, Inc., home of Mammoth PostgreSQL - S/ODBC and S/JDBC
> Postgresql support, programming shared hosting and dedicated hosting.
> +1-503-667-4564 - jd@commandprompt.com - http://www.commandprompt.com
> Mammoth PostgreSQL Replicator. Integrated Replication for PostgreSQL
> <jd.vcf>