[pgpool-general: 1651] Re: inserts sent to standby

Michael Betts mbetts at softdevgroup.com
Sun Apr 21 07:45:31 JST 2013


Tatsuo,

I did find an error in the standby log:

2013-04-20 08:01:11 UTC [29975]: [171-1] user=xxxx,db=rad ERROR:  canceling statement due to conflict with recovery
2013-04-20 08:01:11 UTC [29975]: [172-1] user=xxxx,db=rad DETAIL:  User query might have needed to see row versions that must be removed.
2013-04-20 08:01:11 UTC [29975]: [173-1] user=xxxx,db=rad STATEMENT:  select distinct(ar.id), ar.name as nm, ar.name         from artist ar         join album al on ar.id=al.artist_id
2013-04-20 08:01:11 UTC [29975]: [174-1] user=xxxx,db=rad LOG:  temporary file: path "base/pgsql_tmp/pgsql_tmp29975.14", size 107708416
2013-04-20 08:01:11 UTC [29975]: [175-1] user=xxxx,db=rad FATAL:  terminating connection due to conflict with recovery
2013-04-20 08:01:11 UTC [29975]: [176-1] user=xxxx,db=rad DETAIL:  User query might have needed to see row versions that must be removed.
2013-04-20 08:01:11 UTC [29975]: [177-1] user=xxxx,db=rad HINT:  In a moment you should be able to reconnect to the database and repeat your command.
2013-04-20 08:01:11 UTC [29975]: [178-1] user=xxxx,db=rad LOG:  disconnection: session time: 0:04:21.267 user=xxxx database=rad host=10.140.76.210 port=44700

Thanks,

Mike


On Apr 20, 2013, at 6:29 PM, Tatsuo Ishii wrote:

>> Tatsuo,
>> 
>> I did this but don't have enough information as rsyslogd is dropping messages due to rate limiting.  I will try and reproduce this problem in a test environment.
>> 
>> Meanwhile, I turned delay_threshold off and debug off and restarted pgpool. I no longer see inserts being sent to the standby, however, I encountered another problem which is that pgpool becomes unresponsive and clients can't connect.  The cpu usage spikes to 100%.  Right before this happened, I see this in the log file:
>> 
>> Apr 20 08:01:07 ip-10-140-76-210 pgpool[2133]: pool_process_query: discard E packet from backend 1
> 
> This means pgpool receives certain error message from backend 1. Can
> you find an error around this time in PostgreSQL log?
> 
>> Apr 20 08:01:07 ip-10-140-76-210 pgpool[2133]: pool_read: EOF encountered with backend
>> Apr 20 08:01:07 ip-10-140-76-210 pgpool[2133]: pool_read: EOF encountered with backend
>> Apr 20 08:01:07 ip-10-140-76-210 pgpool[2133]: detect_stop_postmaster_error: detect_error error
>> Apr 20 08:01:07 ip-10-140-76-210 pgpool[2133]: detect_postmaster_down_error returns error on backend 1. Going to close this session.
>> 
>> To me it looks like there was a communication error with the standby. Is this what this means? Show pool_nodes shows both nodes with status of 2 after this. Shouldn't show pool_nodes show the standby with a status of 3 after this? And does pgpool recover from this or do I need to restart?
>> 
>> Thanks again for your great product and assistance,
>> 
>> Mike
>> 
>> 
>> On Apr 18, 2013, at 6:49 PM, Tatsuo Ishii wrote:
>> 
>>> I had hard times to reproduce your problem. Can you change pgpool.conf
>>> (debug = 1) and do pgpool reload, then send an insert to pgpool? That
>>> should produce detailed debug information.
>>> --
>>> Tatsuo Ishii
>>> SRA OSS, Inc. Japan
>>> English: http://www.sraoss.co.jp/index_en.php
>>> Japanese: http://www.sraoss.co.jp
>>> 
>>>> Tatsuo,
>>>> 
>>>> Thank you for confirming this.  I have experienced the same behavior again.  Is there something I can do to help provide information about this problem?
>>>> 
>>>> Thanks,
>>>> 
>>>> Mike
>>>> 
>>>> On Apr 16, 2013, at 7:41 PM, Tatsuo Ishii wrote:
>>>> 
>>>>>> I have been running pgpool 3.2.3 in production and everything has been working great.  However, I recently had an incident where pgpool started sending inserts to the the read-only standby and not the master.  I'm using master/slave mode with streaming replication and both the master and slave were up and running and when I checked the pgpool status, everything seemed normal.  I'm also using delay_threshold = 100000.  When this incident occurred, it was after a large data update in which the lag exceed this threshold.  I believe that once the threshold was no longer exceeded, it started sending queries back to the standby and also started sending inserts there too.
>>>>>> 
>>>>>> Am I understanding this feature correctly?  If the lag exceeds the delay_threshold, it stops sending queries to the standby and when it drops below the threshold, it resumes.  Any idea as to why it would send inserts to the standby?  I did not have debug on, so I don't have much information to go on, except I do know that the delay_threshold was exceeded and shortly after it was no longer exceeded, this started happening.  Restarting pgpool cleared it up.
>>>>> 
>>>>> Your understanding of delay_threshold behavior is correct and sounds
>>>>> like the incident you observed is a bug. I will try to reproduce the
>>>>> problem to find out what is wrong.
>>>>> --
>>>>> 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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