[pgpool-general: 313] Re: Transaction replicated to streaming slave

[Bill W]

Hello Tatuso,

Thanks explaining the situation.

I understand the need for the change because of the JDBC drivers.

Is there any way to add a configuration option to enable/disable the old
behavior?

master_slave_replicate_transactions = on/off

Thanks,
Bill


On 3/27/12 10:48 AM, Tatsuo Ishii wrote:
>> Hello Tatsuo,
>>
>> Thanks for the reply!
>>
>> Actually the the client is an ODBC driver, which explains the age.
>> application -> odbc -> pgpool -> postgres.
>>
>> I don't quite understand why a 'begin' would ever be sent to the
>> secondary server. Should't pgpool see the 'begin' and assume that
>> anything important enough to be in a transaction should go to the primary?
> 
> Actually "begin" used to be sent to the primary only before
> 3.1.x. After following commit, "begin" is sent to standby as well. I
> didn't know the change breaks your applications. Sorry.
> 
> authorToshihiro Kitagawa <kitagawa at sraoss.co.jp>
>  Fri, 12 Aug 2011 06:46:04 +0000 (06:46 +0000)
> committerToshihiro Kitagawa <kitagawa at sraoss.co.jp>
>  Fri, 12 Aug 2011 06:46:04 +0000 (06:46 +0000)
> commit876aa5433aceff40ad0f136cbd95d8c48f17e546
> tree1f138faa5cd62c8e66c49dba3a4e31577f29d1d5tree | snapshot
> parent0f99cff342692c820e9b1787c39928878c3906fbcommit | diff
> 
> Fix bug which cannot use the cursors of JDBC driver on standby node.
> In master/slave mode, the transaction commands come to be sent to
> all nodes by this fix because the cursors of JDBC driver cannot use
> without transactions.
> 
> But if the transaction command is "BEGIN READ WRITE" or "START TRANSACTION
> READ WRITE", pgpool-II sends "BEGIN" instead of it to standby node.
> The reason is because standby nodes disallow "READ WRITE" option.
> 
>> Anyway, is there anything I can do at all with pgpool to force this to
>> go to the primary server?
>>
>> I tried
>> backend_weight0 = 1000
>> backend_weight1 = 0
>> But that doesn't work.
> 
> Because the parameter only applied to SELECTs.
> 
>> I don't know how much luck I'll have in being able to change the sql in
>> the application.  I can try to ask them to patch it but that patch may
>> or may not be applied.
> 
> Are you using JDBC driver? If not, downgrading to 3.0.x. might help you.
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese: http://www.sraoss.co.jp
> 
>> Thanks,
>> Bill
>>
>>
>>
>> On 3/27/12 1:07 AM, Tatsuo Ishii wrote:
>>> Pgpool-II does not support multi statement query.
>>>
>>> begin;delete from channels where hostname='';delete from channels where hostname='';commit;
>>>
>>> So pgpool only analyzes the first component of the multi statement
>>> query. i.e. "begin". This is a known limitation and clearly stated in
>>> pgpool's document.
>>>
>>> Also it seems you use very old client. I notice this from the log:
>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: pool_read_string: read all from
>>>
>>> pool_read_string is only called if client use old version 2 protocol,
>>> which was used by PostgreSQL 7.3 or older. I recommend to use more
>>> modern client software.
>>> --
>>> Tatsuo Ishii
>>> SRA OSS, Inc. Japan
>>> English: http://www.sraoss.co.jp/index_en.php
>>> Japanese: http://www.sraoss.co.jp
>>>
>>>> Hello everyone,
>>>>
>>>>
>>>> I'm finding that pgpool is replicating transactions to the streaming
>>>> slave, even though I believe I've configured pgpool to only communicate
>>>> with the master.
>>>>
>>>> I've verified the log on the slave, and it is indeed receiving that
>>>> transaction;
>>>>
>>>> If I shut down the slave and re-run the query, everything proceeds normally.
>>>>
>>>> Does anyone have any advice?
>>>>
>>>> Thanks,
>>>> Bill
>>>>
>>>> pgpool-II-3.1.2
>>>> postgresql-server-9.1.1
>>>>
>>>> Log:
>>>> --------------
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: statement2: begin;delete from
>>>> channels where hostname='';delete from channels where hostname='';commit;
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: pool_set_query_in_progress: done
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: send_to_where: 3 query:
>>>> begin;delete from channels where hostname='';delete from channels where
>>>> hostname='';commit;
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: wait_for_query_response: waiting
>>>> for backend 0 completing the query
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: wait_for_query_response: waiting
>>>> for backend 1 completing the query
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: read_kind_from_backend: read kind
>>>> from 0 th backend C NUM_BACKENDS: 2
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: read_kind_from_backend: read kind
>>>> from 1 th backend C NUM_BACKENDS: 2
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: ProcessBackendResponse: kind from
>>>> backend: C
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: pool_read_string: read all from
>>>> pending data. po:7 len:29
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: pool_read_string: read all from
>>>> pending data. po:7 len:60
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: CompletedResponse: string: "BEGIN"
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: read_kind_from_backend: read kind
>>>> from 0 th backend C NUM_BACKENDS: 2
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: read_kind_from_backend: read kind
>>>> from 1 th backend E NUM_BACKENDS: 2
>>>>
>>>> 2012-03-26 20:07:08 ERROR: pid 19119: read_kind_from_backend: 1 th kind
>>>> E does not match with master or majority connection kind C
>>>>
>>>> 2012-03-26 20:07:08 DEBUG: pid 19119: pool_read_string: read all from
>>>> pending data. po:66 len:1
>>>>
>>>> 2012-03-26 20:07:08 ERROR: pid 19119: kind mismatch among backends.
>>>> Possible last query was: "begin;delete from channels where
>>>> hostname='';delete from channels where hostname='';commit;" kind details
>>>> are: 0[C] 1[E: ERROR:  cannot execute DELETE in a read-only transaction
>>>> ]
>>>>
>>>> 2012-03-26 20:07:08 LOG:   pid 19119: do_child: exits with status 1 due
>>>> to error
>>>> --------------
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