[pgpool-general: 1275] Re: database detach and I don't understand why

Tatsuo Ishii ishii at postgresql.org
Wed Jan 2 08:20:04 JST 2013

Well there some possibilities:

1) JBoss uses functions which has side effect(updating tables).

2) JBoss uses triggers which updates the table in question.

3) the transaction updating the table in question committed on node 1
   but not committed on node 0 for some reason. Maybe the connection
   between JBoss and pgpool between those two commit commands were

Anyway, if you carefully look into the PostgreSQL log (I assume
log_statement is on), you may be able find the cause.
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

> the different is that node 1 the message in jbm_msg still exist, but
> on node 0 it's deleted. the jbm_msg_ref on both servers are empty.
> but I don't understand how that's possible when the jms process
> communicate through the pgpool? and if I read the postgresql logs
> correct for both nodes all SQL statement are executed in the same
> order until it detach.
> /Flemming
> 2012/12/31 Tatsuo Ishii <ishii at postgresql.org>:
>>> Hello,
>>> We have been using pgpool2 for sometime now and been happy with it,
>>> but lately it suddenly start to detach the database on one of the
>>> nodes on 2 node cluster. I have been investigated this for a while and
>>> I can't understand why pgpool2 thinks is should detach.
>>> We are using pgpool version 3.0.4-1 with postgresql version
>>> 8.4.8-0squeeze2 our application server is JBossAS 5 including (jboss
>>> messaging 1.4.8-SP2). The application server only communicate through
>>> pgpool so we are sure that no other processes are working around
>>> pgpool
>>> We are pretty sure the databases are not different from the beginning
>>> and it's new records that are created. We post 3 messages on 2
>>> different jms queues and 3 clients that consumes the messages. When
>>> jboss messaging component want to remove the messages because it
>>> delivered to all the clients, pgpool detach the database because it
>>> get a different response from node 1 when it want to delete the
>>> message.... which I don't understand how that's possible
>>> I really will appreciate some help to understand what is going on and
>>> why it detach the database
>>> Thanks!
>>> br,
>>> Flemming
>>> the log_line_prefix = '%t %p %v %x' for the postgresql
>>> You can find the log files by following the links below for pgpool2
>>> debug log and postgresql log from both servers
>>> jboss-detach-190.sql(postgresql log) >
>>> http://ubuntuone.com/6Ku56EoHI7FAXAyC1p1prQ
>>> jboss-detach-191.sql(postgresql log) >
>>> http://ubuntuone.com/0ICbQCiowqDgKe7LglMxSV
>>> pgpool.conf > http://ubuntuone.com/3BhoRnr3ACifYhi2QqSbat
>>> pgppool-191-log  > http://ubuntuone.com/1g8ExrevBeRUj92XS5WjyZ7
>> From the log, the cause of the detach was this:
>> Dec 27 19:54:18 SWDEV035 pgpool: 2012-12-27 19:54:18 ERROR: pid 18412: pgpool detected difference of the number of inserted, updated or deleted tuples. Possible last query was: "DELETE FROM JBM_MSG WHERE MESSAGE_ID = $1 AND NOT EXISTS (SELECT JBM_MSG_REF.MESSAGE_ID FROM JBM_MSG_REF WHERE JBM_MSG_REF.MESSAGE_ID = $2)"
>> Dec 27 19:54:18 SWDEV035 pgpool: 2012-12-27 19:54:18 LOG:   pid 18412: CommandComplete: Number of affected tuples are: 0 1
>> As you said, it seems your node 0 DB did not have a raw satisfied the
>> WHERE clause, while your node 1 had one row which satisfied it at that
>> time. I suggest to check tables used by JBoss right after failover to
>> see there's difference in table's data.
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese: http://www.sraoss.co.jp
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