[pgpool-hackers: 4250] Re: Issue with failover_require_consensus

[Tatsuo Ishii]

Hi Usama,

Thank you! Looks perfect (and my test passed).

Best reagards,
--
Tatsuo Ishii
SRA OSS LLC
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp


> Hi
> Sorry for the inconvenience. I guess I attached the wrong patch file
> previously.
> Please find the latest one that also changes the DEBUG to LOG, as suggested.
> 
> Thanks
> best Regards
> Muhammad Usama
> 
> 
> On Mon, Dec 19, 2022 at 9:07 AM Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
> 
>> > Hi Ishii San
>> >
>> > Thanks for the feedback. Please find the updated patch that takes care of
>> > transferring the per node health check params through WD_POOL_CONFIG_DATA
>> > and use those in calculations.
>> > Could you verify if the attached fixes the issue?
>>
>> Sure.
>>
>> The patch adds trailing spaces.
>>
>> /home/t-ishii/fix_failover_command_timout_v2.diff:68: trailing whitespace.
>>                         int pn_failover_command_timeout =
>> pool_config->health_check_params[i].health_check_period +
>> /home/t-ishii/fix_failover_command_timout_v2.diff:69: trailing whitespace.
>>
>> (pool_config->health_check_params[i].health_check_retry_delay *
>> /home/t-ishii/fix_failover_command_timout_v2.diff:118: trailing whitespace.
>>                         health_check_params_count =
>> config->backend_desc->num_backends;
>> warning: 3 lines add whitespace errors.
>>
>> There is a compile error:
>> watchdog.c:8203:10: error: ‘DEBUG’ undeclared (first use in this
>> function); did you mean ‘DEBUG1’?
>>  8203 |  ereport(DEBUG,(errmsg("Setting failover command timeout to
>> %d",failover_command_timeout)));
>>       |          ^~~~~
>>
>> We'd better to use "LOG", instead DEBUG* here? Because:
>> - the log message is not frequent
>> - the timeout value is an important information
>>
>> What do you think?
>>
>> > As for standard_packet_processor() is concerned, it Is intended to handle
>> > messages
>> > that do not require to be handled differently for each watchdog state.
>>
>> Ok. Thank you for the explanation.
>>
>> Best reagards,
>> --
>> Tatsuo Ishii
>> SRA OSS LLC
>> English: http://www.sraoss.co.jp/index_en/
>> Japanese:http://www.sraoss.co.jp
>>
>> > Thanks
>> > Best Regards
>> > Muhammad Usama
>> >
>> >
>> > On Sat, Dec 17, 2022 at 5:01 PM Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
>> >
>> >> >>> On Tue, Nov 29, 2022 at 3:27 AM Tatsuo Ishii <ishii at sraoss.co.jp>
>> >> wrote:
>> >> >>>
>> >> >>>> >> Hi Ishii-San
>> >> >>>> >>
>> >> >>>> >> Sorry for the delayed response.
>> >> >>>> >
>> >> >>>> > No problem.
>> >> >>>> >
>> >> >>>> >> With the attached fix I guess the failover objects will linger
>> on
>> >> >>>> forever
>> >> >>>> >> in case of a false alarm by a health check or small glitch.
>> >> >>>> >
>> >> >>>> > That's not good.
>> >> >>>> >
>> >> >>>> >> One way to get around the issue could be to compute
>> >> >>>> >> FAILOVER_COMMAND_FINISH_TIMEOUT based on the maximum value
>> >> >>>> >> of health_check_peroid across the cluster.
>> >> >>>> >> something like: failover_command_finish_timouut =
>> >> >>>> max(health_check_period)
>> >> >>>> >> * 2 = 60
>> >> >>>>
>> >> >>>> After thinking more, I think we need to take account
>> >> >>>> health_check_max_retries and health_check_retry_delay as
>> >> >>>> well. i.e. instead of max(health_check_period), something like:
>> >> >>>> max(health_check_period + (health_check_retry_delay *
>> >> >>>> health_check_max_retries)).
>> >> >>>>
>> >> >>>> What do you think?
>> >> >>>>
>> >> >>>
>> >> >>> Thanks for the valuable suggestions.
>> >> >>> Can you try out the attached patch to see if it solves the issue?
>> >> >>
>> >> >> Unfortunately the patch did not pass my test case.
>> >> >>
>> >> >> - 3 watchdog nodes and 2 PostgreSQL servers, streaming replication
>> >> >>   cluster (created by watchdog_setup). pgpool0 is the watchdog
>> leader.
>> >> >>
>> >> >> - health_check_period = 300, health_check_max_retries = 0
>> >> >>
>> >> >> - pgpool1 starts 120 seconds after pgpool0 starts
>> >> >>
>> >> >> - pgpool2 does not start
>> >> >>
>> >> >> - after watchdog cluster becomes ready, shutdown PostgreSQL node 1
>> >> (standby).
>> >> >>
>> >> >> - wait for 600 seconds to expect a failover.
>> >> >>
>> >> >> Unfortunately failover did not happen.
>> >> >>
>> >> >> Attached is the test script and pgpool0 log.
>> >> >>
>> >> >> To run the test:
>> >> >>
>> >> >> - unpack test.tar.gz
>> >> >>
>> >> >> - run prepare.sh
>> >> >>   $ sh prepare.sh
>> >> >>   This should create "testdir" directory with 3 watchdog node +
>> >> PostgreSQL 2 node cluster.
>> >> >>
>> >> >> - cd testdir and run the test
>> >> >>   $ sh ../start.sg -o 120
>> >> >>   This will start the test, "-o" specifies how long wait before
>> >> strating pgpool1.
>> >> >
>> >> > After the test failure, I examined the pgpool log on the pgpool leader
>> >> > node (node 0). It seems timeout was not updated as expected.
>> >> >
>> >> > 2022-12-17 08:07:11.419: watchdog pid 707483: LOG:  failover request
>> >> from 1 nodes with ID:42 is expired
>> >> > 2022-12-17 08:07:11.419: watchdog pid 707483: DETAIL:  marking the
>> >> failover object for removal. timeout: 15
>> >> >
>> >> > After looking into the code, I found update_failover_timeout() only
>> >> > examines "health_check_period".  I think you need to examine
>> >> > "health_check_period0" etc. as well and find the larget one for the
>> >> > timeout caliculation.
>> >> >
>> >> > By the way,
>> >> >
>> >> >> failover_command_timout
>> >> >> g_cluster.failover_command_timout
>> >> >
>> >> > I think "timout" should be "timeout".
>> >>
>> >> I was trying to create a proof of concept patch for this:
>> >>
>> >> > After looking into the code, I found update_failover_timeout() only
>> >> > examines "health_check_period".  I think you need to examine
>> >> > "health_check_period0" etc. as well and find the larget one for the
>> >> > timeout caliculation.
>> >>
>> >> and noticed that update_failover_timeout() is called by
>> >> standard_packet_processor() when WD_POOL_CONFIG_DATA packet is
>> >> received like: update_failover_timeout(wdNode, standby_config); But
>> >> standby_config was created by get_pool_config_from_json() which does
>> >> not seem to create health_check_params in pool_config data. Also I
>> >> wonder why standard_packet_processor() needs to be called when
>> >> WD_POOL_CONFIG_DATA is recieved. Can't we simply omit the call to
>> >> update_failover_timeout() in this case?
>> >>
>> >> Best reagards,
>> >> --
>> >> Tatsuo Ishii
>> >> SRA OSS LLC
>> >> English: http://www.sraoss.co.jp/index_en/
>> >> Japanese:http://www.sraoss.co.jp
>> >>
>>