[pgpool-general: 766] Re: pgpool dropping backends too much

Karl von Randow karl+pgpool at cactuslab.com
Thu Jul 19 13:07:41 JST 2012


Right, sorry I should have investigated that! Here is a snip from the 
logs for that moment in time that shows the ERROR due to conflict with 
recovery that I mentioned, also there's a FATAL in there. We see a lot 
of the conflict with recovery... however they don't always have the 
FATAL, more below.

2012-07-17 00:11:03 NZST [15692]: [257-1] ERROR:  canceling statement 
due to conflict with recovery
2012-07-17 00:11:03 NZST [15692]: [258-1] DETAIL:  User query might have 
needed to see row versions that must be removed.
2012-07-17 00:11:03 NZST [15692]: [259-1] STATEMENT: <SNIP>
2012-07-17 00:11:03 NZST [15696]: [366-1] FATAL:  terminating connection 
due to conflict with recovery
2012-07-17 00:11:03 NZST [15696]: [367-1] DETAIL:  User query might have 
needed to see row versions that must be removed.
2012-07-17 00:11:03 NZST [15696]: [368-1] HINT:  In a moment you should 
be able to reconnect to the database and repeat your command.
2012-07-17 00:11:03 NZST [15682]: [99-1] ERROR:  canceling statement due 
to conflict with recovery
2012-07-17 00:11:03 NZST [15682]: [100-1] DETAIL:  User query might have 
needed to see row versions that must be removed.
2012-07-17 00:11:03 NZST [15682]: [101-1] STATEMENT:  <SNIP>
2012-07-17 00:11:04 NZST [16731]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:06 NZST [16734]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:07 NZST [16737]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:09 NZST [16789]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:16 NZST [16806]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:17 NZST [16822]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:17 NZST [16826]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:18 NZST [16829]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:21 NZST [16835]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:22 NZST [16837]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:22 NZST [16852]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer
2012-07-17 00:11:23 NZST [16855]: [1-1] LOG:  could not receive data 
from client: Connection reset by peer

I presume that all of the connection reset by peer is pgpool dropping 
all of its connections to this instance.

Here is another time there was a conflict with recovery. This time it 
did not coincide with the backend being degraded:

2012-07-19 07:16:58 NZST [22343]: [18-1] ERROR:  canceling statement due 
to conflict with recovery
2012-07-19 07:16:58 NZST [22343]: [19-1] DETAIL:  User query might have 
needed to see row versions that must be removed.
2012-07-19 07:16:58 NZST [22343]: [20-1] STATEMENT:  <SNIP>
2012-07-19 07:16:58 NZST [22343]: [21-1] LOG:  duration: 64.141 ms  
execute <unnamed>: <SNIP>
2012-07-19 07:16:58 NZST [22343]: [22-1] DETAIL:  parameters: <SNIP>

However looking through the logs for instances of the FATAL, it happens 
more often than we degenerate back-ends as well. I'm not sure if this helps!

k

On 19/07/2012 3:44 p.m., Tatsuo Ishii wrote:
> When you see this;
>> pool_process_query: discard E packet from backend 1
> Is there any error reported in backend 1's log?
> I'm asking because E corresponds to "ERROR" of PostgreSQL.
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese: http://www.sraoss.co.jp
>
>> We are running pgpool with 3 backend servers (9.0, streaming
>> replication). We are running non-SSL client-pgpool and SSL
>> pgpool-server (my previous email was in error, we do not appear to be
>> using SSL client-pgpool).
>>
>> I have set the primary server to not support fail-over, and that
>> works, it doesn't failover. However our slaves failover once or twice
>> a day, when the slave has not in fact failed. I have to reattach the
>> node, and it continues happily.
>>
>> The syslog always contains this note about E packets:
>>
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 31871:
>> pool_process_query: discard E packet from backend 1
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 ERROR: pid 31871:
>> pool_ssl: SSL_read: no SSL error reported
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 ERROR: pid 31871:
>> pool_read: read failed (Success)
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 31871:
>> degenerate_backend_set: 1 fail over request from pid 31871
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 30346:
>> starting degeneration. shutdown host db2(5432)
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 30346:
>> Restart all children
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 30346:
>> find_primary_node_repeatedly: waiting for finding a primary node
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 30346:
>> find_primary_node: primary node id is 0
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 30346:
>> failover: set new primary node: 0
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 30346:
>> failover: set new master node: 0
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 923: worker
>> process received restart request
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 30346:
>> failover done. shutdown host db2(5432)
>> Jul 17 00:11:04 app2 pgpool: 2012-07-17 00:11:04 LOG: pid 30346:
>> worker child 923 exits with status 256
>> Jul 17 00:11:04 app2 pgpool: 2012-07-17 00:11:04 LOG: pid 924: pcp
>> child process received restart request
>> Jul 17 00:11:04 app2 pgpool: 2012-07-17 00:11:04 LOG: pid 30346: fork
>> a new worker child pid 9434
>> Jul 17 00:11:04 app2 pgpool: 2012-07-17 00:11:04 LOG: pid 30346: PCP
>> child 924 exits with status 256
>> Jul 17 00:11:04 app2 pgpool: 2012-07-17 00:11:04 LOG: pid 30346: fork
>> a new PCP child pid 9435
>>
>> Sometimes the proceeding syslog entry is a LOG notice about a
>> statement that failed, eg:
>> Jul 17 00:11:03 app2 pgpool: 2012-07-17 00:11:03 LOG: pid 26664:
>> pool_send_and_wait: Error or notice message from backend: : DB node
>> id: 1 backend pid: 15682 statement: <SNIP> message: canceling
>> statement due to conflict with recovery
>>
>> I don't want to mark our slaves as no-failover but it seems that
>> pgpool is either experiencing a fault and interpreting it as a
>> failover, or is a bit sensitive? I'm happy to test patches!
>>
>> Best regards,
>> Karl
>> _______________________________________________
>> pgpool-general mailing list
>> pgpool-general at pgpool.net
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