Re: Weird problem that enormous locks

On Fri, 15 Jul 2011 18:36:19 +0800, Tony Wang wrote:

Weird that I receive your each message twice.

On Fri, Jul 15, 2011 at 15:33, Radoslaw Smogura  wrote:

Simple and obvious question right now do You call commit after
transaction? If yes do you use any query or connection pooler?

Yes. connection pool is used as application level, not db level.

no commit after transaction is possible (Im trying to check the

logic), I just cannot imagine it happened for so many users at the
same time, and then calmed down for long time, and came again.

I found the query I used to log locks would miss locks that relname is

null. will add that, though no idea why its null
 

------------------------
Regards,
Radoslaw Smogura
(mobile)
-------------------------
From: Tony Wang
Sent: 15 lipca 2011 03:51
To: Scott Marlowe
Cc: PostgreSQL

Subject: Re: [GENERAL] Weird problem that enormous locks

On Fri, Jul 15, 2011 at 08:22, Scott Marlowe wrote:

On Thu, Jul 14, 2011 at 6:01 PM, Tony Wang wrote:

On Fri, Jul 15, 2011 at 01:13, Scott Marlowe

> wrote:

On Wed, Jul 13, 2011 at 9:47 PM, Tony Wang wrote:

> On Thu, Jul 14, 2011 at 10:35, John R Pierce

>> > wrote:

> Its a game server, and the queries are updating users money,

as

> normal.
> The sql is like "UPDATE player SET money = money + 100 where

id =
>> > 12345".

> The locks were RowExclusiveLock for the table "player" and

the indexes.

> The
> weird thing is there was another ExclusiveLock for the table

"player",
>> > i.e.

> "player" got two locks, one RowExclusiveLock and one

ExclusiveLock.

> In the postgresql documentation
>

(http://www.postgresql.org/docs/8.4/static/explicit-locking.html

[5]), its

>> > said

> about the  Exclusive "This lock mode is not automatically

acquired on

> user
> tables by any PostgreSQL command."

You need to figure out what part of your app, or maybe a rogue

>> developer etc is throwing an exclusive lock.

Yeah, thats what Im trying to do

Cool.  In your first post you said:

select pg_class.relname, pg_locks.mode, pg_locks.granted,

pg_stat_activity.current_query, pg_stat_activity.query_start,

pg_stat_activity.xact_start as transaction_start,

age(now(),pg_stat_activity.query_start) as query_age,
> age(now(),pg_stat_activity.xact_start) as transaction_age,
pg_stat_activity.procpid from pg_stat_activity,pg_locks left

outer join pg_class on (pg_locks.relation = pg_class.oid) where

pg_locks.pid=pg_stat_activity.procpid and
> substr(pg_class.relname,1,3) != pg_ order by query_start;

The only special thing I can find is that there were a lot

ExclusiveLock, while its normal the locks are

only AccessShareLock and RowExclusiveLock.

So what did / does current_query say when its happening?  If it
says
you dont have access permission then run that query as root when
it
happens again.

As I said, its normal update like "UPDATE player SET money = money +

100 WHERE id=12345", but there are quite many

Links:
------
[1] mailto:wwwjfy@gmail.com
[2] mailto:scott.marlowe@gmail.com
[3] mailto:wwwjfy@gmail.com
[4] mailto:pierce@hogranch.com
[5] http://www.postgresql.org/docs/8.4/static/explicit-locking.html
[6] mailto:scott.marlowe@gmail.com
[7] mailto:rsmogura@softperience.eu

Actually I don't know what pool You use (I think PHP - I don't know much about this), but I imagine following, If You don't use auto commit or commit:
1. User A updates moneys, gets connections C1, locks his row, no commit
2. User A updates moneys again, gets connection C2, but C1 still holds lock.
Regards,
Radosław Smogura