[pgpool-general: 776] Re: pgpool dropping backends too much
Luiz Pasqual
luiz at pasquall.com
Fri Jul 20 22:42:30 JST 2012
It is in postgresql.conf, you should set it in the slaves.
On Fri, Jul 20, 2012 at 11:02 AM, Lazáro Rubén García Martínez
<lgarciam at vnz.uci.cu> wrote:
> Where is the property 'hot_standby_feedback'?
>
> Regards.
> ________________________________________
> From: pgpool-general-bounces at pgpool.net [pgpool-general-bounces at pgpool.net] On Behalf Of Luiz Pasqual [luiz at pasquall.com]
> Sent: Friday, July 20, 2012 8:37 AM
> To: pgpool-general at pgpool.net
> Subject: [pgpool-general: 774] Re: pgpool dropping backends too much
>
> Karl,
>
> We had this kind of errors also in our setup:
> FATAL: terminating connection due to conflict with recovery
> DETAIL: User query might have needed to see row versions that must be removed.
> HINT: In a moment you should be able to reconnect to the database and
> repeat your command.
>
> When it happens the slave was disconnected from pgpool (as expected)
> and we have to attached manually again. Then we set
> "hot_standby_feedback = on", and it solve, because in our case this
> conflicts was related with autovacuum.
>
> Well, it may not be your case, but I think pgpool is doing the right thing.
>
> [ ]'s
>
>
> On Thu, Jul 19, 2012 at 6:09 AM, Karl von Randow
> <karl+pgpool at cactuslab.com> wrote:
>> Thanks very much Tatsuo, when you said "please give us some time to develop a patch" I didn't expect you to come back with a patch so quickly!
>>
>> I have patched, compiled and deployed it across our app server cluster (3 servers) and I'll report back tomorrow on whether I get a full night's sleep!
>>
>> On 19/07/2012, at 5:10 PM, Tatsuo Ishii <ishii at postgresql.org> wrote:
>>
>>> After thinking more, I decided not try to read error messages from
>>> backend because there's no guarantee to be able to read whole
>>> messages(in this case error packet) from the broken
>>> connection. Actually you case seems to verify my idea. Pgpool was able
>>> to read first 1 byte, which indicates the packet is an error
>>> message('E'). So it tries to read rest of the message and failed, thus
>>> triggers failover. However without reading whole error message
>>> contents, it is not possible what to do. Probably what we can do the
>>> best is:
>>>
>>> - If ssl_read() returns unknown error code, assume the connection is
>>> broken (your log shows that you are the case). Not trigger failover
>>> but terminate the session.
>>>
>>> This is essentially same as what libpq does. Attached is the patch
>>> trying to do this.
>>> --
>>> Tatsuo Ishii
>>> SRA OSS, Inc. Japan
>>> English: http://www.sraoss.co.jp/index_en.php
>>> Japanese: http://www.sraoss.co.jp
>>>
>>>> Absolutely, thank you very much. We will be ready to test the patch
>>>> whenever you are. We will work around this in the meantime by marking
>>>> the back-ends as not to failover!
>>>>
>>>> On 19/07/2012 4:31 p.m., Tatsuo Ishii wrote:
>>>>> Thanks. This helps me a lot.
>>>>>
>>>>> It seems the cause of error is this:
>>>>>> 2012-07-17 00:11:03 NZST [15696]: [366-1] FATAL: terminating
>>>>>> connection due to conflict with recovery
>>>>> SSL library is not smart enough to detect the connection shutdown
>>>>> event. Thus it returns:
>>>>>> pool_ssl: SSL_read: no SSL error reported
>>>>> Probably in this case pgpool should inspect the error event and avoid
>>>>> to call SS_read(). Then pgpool should disconnect the connection to
>>>>> client hopefully with the error messages returned from backend, rather
>>>>> than trigger failover. Please give us some time to develop a patch.
>>>>> --
>>>>> Tatsuo Ishii
>>>>> SRA OSS, Inc. Japan
>>>>> English: http://www.sraoss.co.jp/index_en.php
>>>>> Japanese: http://www.sraoss.co.jp
>>>>>
>>>>>> 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
>>>>>>>> http://www.pgpool.net/mailman/listinfo/pgpool-general
>>>>>> _______________________________________________
>>>>>> pgpool-general mailing list
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>>> diff --git a/pool_ssl.c b/pool_ssl.c
>>> index b3e2d50..194a01c 100644
>>> --- a/pool_ssl.c
>>> +++ b/pool_ssl.c
>>> @@ -167,8 +167,13 @@ int pool_ssl_read(POOL_CONNECTION *cp, void *buf, int size) {
>>> n = -1;
>>> break;
>>> default:
>>> - perror_ssl("SSL_read");
>>> - n = -1;
>>> + pool_error("pool_ssl_read: unrecognized error code: %d", err);
>>> + /*
>>> + * We assume that the connection is broken. Returns 0
>>> + * rather than -1 in this case because -1 triggers
>>> + * unwanted failover in the caller (pool_read).
>>> + */
>>> + n = 0;
>>> break;
>>> }
>>>
>>
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>
>
>
> --
> Luiz Fernando Pasqual S. Souza
> mail: luiz at pasquall.com
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>
> Fin a la injusticia, LIBERTAD AHORA A NUESTROS CINCO COMPATRIOTAS QUE SE ENCUENTRAN INJUSTAMENTE EN PRISIONES DE LOS EEUU!
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> http://justiciaparaloscinco.wordpress.com
--
Luiz Fernando Pasqual S. Souza
mail: luiz at pasquall.com
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