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.
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