[pgpool-general: 184] Re: Healthcheck timeout not always respected

Stevo Slavić sslavic at gmail.com
Fri Jan 20 08:30:26 JST 2012 

Using exit_request was wrong and caused a bug. 4th patch needed -
health_check_timer_expired is global now so it can be verified if it was
set to 1 outside of main.c

Kind regards,
Stevo.

2012/1/19 Stevo Slavić <sslavic at gmail.com>

> Using exit_code was not wise. Tested and encountered a case where this
> results in a bug. Have to work on it more. Main issue is how in
> pool_connection_pool.c connect_inet_domain_socket_by_port function to know
> that health check timer has expired (set to 1). Any ideas?
>
> Kind regards,
> Stevo.
>
>
> 2012/1/19 Stevo Slavić <sslavic at gmail.com>
>
>> Tatsuo,
>>
>> Here are the patches which should be applied to current pgpool head for
>> fixing this issue:
>>
>> Fixes-health-check-timeout.patch
>> Fixes-health-check-retrying-after-failover.patch
>> Fixes-clearing-exitrequest-flag.patch
>>
>> Quirk I noticed in logs was resolved as well - after failover pgpool
>> would perform healthcheck and report it is doing (max retries + 1) th
>> health check which was confusing. Rather I've adjusted that it does and
>> reports it's doing a new health check cycle after failover.
>>
>> I've tested and it works well - when in raw mode, backends set to
>> disallow failover, failover on backend failure disabled, and health checks
>> configured with retries (30sec interval, 5sec timeout, 2 retries, 10sec
>> delay between retries).
>>
>> Please test, and if confirmed ok include in next release.
>>
>> Kind regards,
>>
>> Stevo.
>>
>>
>> 2012/1/16 Stevo Slavić <sslavic at gmail.com>
>>
>>> Here is pgpool.log, strace.out, and pgpool.conf when I tested with my
>>> latest patch for health check timeout applied. It works well, except for
>>> single quirk, after failover completed in log files it was reported that
>>> 3rd health check retry was done (even though just 2 are configured, see
>>> pgpool.conf) and that backend has returned to healthy state. That
>>> interesting part from log file follows:
>>>
>>> Jan 16 01:31:45 sslavic pgpool[1163]: 2012-01-16 01:31:45 DEBUG: pid
>>> 1163: retrying 3 th health checking
>>> Jan 16 01:31:45 sslavic pgpool[1163]: 2012-01-16 01:31:45 DEBUG: pid
>>> 1163: health_check: 0 th DB node status: 3
>>> Jan 16 01:31:45 sslavic pgpool[1163]: 2012-01-16 01:31:45 LOG:   pid
>>> 1163: after some retrying backend returned to healthy state
>>> Jan 16 01:32:15 sslavic pgpool[1163]: 2012-01-16 01:32:15 DEBUG: pid
>>> 1163: starting health checking
>>> Jan 16 01:32:15 sslavic pgpool[1163]: 2012-01-16 01:32:15 DEBUG: pid
>>> 1163: health_check: 0 th DB node status: 3
>>>
>>>
>>> As can be seen in pgpool.conf, there is only one backend configured.
>>> pgpool did failover well after health check max retries has been reached
>>> (pgpool just degraded that single backend to 3, and restarted child
>>> processes).
>>>
>>> After this quirk has been logged, next health check logs were as
>>> expected. Except those couple weird log entries, everything seems to be ok.
>>> Maybe that quirk was caused by single backend only configuration corner
>>> case. Will try tomorrow if it occurs on dual backend configuration.
>>>
>>> Regards,
>>> Stevo.
>>>
>>>
>>> 2012/1/16 Stevo Slavić <sslavic at gmail.com>
>>>
>>>> Hello Tatsuo,
>>>>
>>>> Unfortunately, with your patch when A is on
>>>> (pool_config->health_check_period > 0) and B is on, when retry count is
>>>> over, failover will be disallowed because of B being on.
>>>>
>>>> Nenad's patch allows failover to be triggered only by health check.
>>>> Here is the patch which includes Nenad's fix but also fixes issue with
>>>> health check timeout not being respected.
>>>>
>>>> Key points in fix for health check timeout being respected are:
>>>> - in pool_connection_pool.c connect_inet_domain_socket_by_port
>>>> function, before trying to connect, file descriptor is set to non-blocking
>>>> mode, and also non-blocking mode error codes are handled, EINPROGRESS and
>>>> EALREADY (please verify changes here, especially regarding closing fd)
>>>> - in main.c health_check_timer_handler has been changed to signal
>>>> exit_request to health check initiated connect_inet_domain_socket_by_port
>>>> function call (please verify this, maybe there is a better way to check
>>>> from connect_inet_domain_socket_by_port if in health_check_timer_expired
>>>> has been set to 1)
>>>>
>>>> These changes will practically make connect attempt to be non-blocking
>>>> and repeated until:
>>>> - connection is made, or
>>>> - unhandled connection error condition is reached, or
>>>> - health check timer alarm has been raised, or
>>>> - some other exit request (shutdown) has been issued.
>>>>
>>>>
>>>> Kind regards,
>>>> Stevo.
>>>>
>>>> 2012/1/15 Tatsuo Ishii <ishii at postgresql.org>
>>>>
>>>>> Ok, let me clarify use cases regarding failover.
>>>>>
>>>>> Currently there are three parameters:
>>>>> a) health_check
>>>>> b) DISALLOW_TO_FAILOVER
>>>>> c) fail_over_on_backend_error
>>>>>
>>>>> Source of errors which can trigger failover are 1)health check 2)write
>>>>> to backend socket 3)read backend from socket. I represent each 1) as
>>>>> A, 2) as B, 3) as C.
>>>>>
>>>>> 1) trigger failover if A or B or C is error
>>>>> a = on, b = off, c = on
>>>>>
>>>>> 2) trigger failover only when B or C is error
>>>>> a = off, b = off, c = on
>>>>>
>>>>> 3) trigger failover only when B is error
>>>>> Impossible. Because C error always triggers failover.
>>>>>
>>>>> 4) trigger failover only when C is error
>>>>> a = off, b = off, c = off
>>>>>
>>>>> 5) trigger failover only when A is error(Stevo wants this)
>>>>> Impossible. Because C error always triggers failover.
>>>>>
>>>>> 6) never trigger failover
>>>>> Impossible. Because C error always triggers failover.
>>>>>
>>>>> As you can see, C is the problem here (look at #3, #5 and #6)
>>>>>
>>>>> If we implemented this:
>>>>> >> However I think we should disable failover if DISALLOW_TO_FAILOVER
>>>>> set
>>>>> >> in case of reading data from backend. This should have been done
>>>>> when
>>>>> >> DISALLOW_TO_FAILOVER was introduced because this is exactly what
>>>>> >> DISALLOW_TO_FAILOVER tries to accomplish. What do you think?
>>>>>
>>>>> 1) trigger failover if A or B or C is error
>>>>> a = on, b = off, c = on
>>>>>
>>>>> 2) trigger failover only when B or C is error
>>>>> a = off, b = off, c = on
>>>>>
>>>>> 3) trigger failover only when B is error
>>>>> a = off, b = on, c = on
>>>>>
>>>>> 4) trigger failover only when C is error
>>>>> a = off, b = off, c = off
>>>>>
>>>>> 5) trigger failover only when A is error(Stevo wants this)
>>>>> a = on, b = on, c = off
>>>>>
>>>>> 6) never trigger failover
>>>>> a = off, b = on, c = off
>>>>>
>>>>> So it seems my patch will solve all the problems including yours.
>>>>> (timeout while retrying is another issue of course).
>>>>> --
>>>>> Tatsuo Ishii
>>>>> SRA OSS, Inc. Japan
>>>>> English: http://www.sraoss.co.jp/index_en.php
>>>>> Japanese: http://www.sraoss.co.jp
>>>>>
>>>>> > I agree, fail_over_on_backend_error isn't useful, just adds
>>>>> confusion by
>>>>> > overlapping with DISALLOW_TO_FAILOVER.
>>>>> >
>>>>> > With your patch or without it, it is not possible to failover only on
>>>>> > health check (max retries) failure. With Nenad's patch, that part
>>>>> works ok
>>>>> > and I think that patch is semantically ok - failover occurs even
>>>>> though
>>>>> > DISALLOW_TO_FAILOVER is set for backend but only when health check is
>>>>> > configured too. Configuring health check without failover on failed
>>>>> health
>>>>> > check has no purpose. Also health check configured with allowed
>>>>> failover on
>>>>> > any condition other than health check (max retries) failure has no
>>>>> purpose.
>>>>> >
>>>>> > Kind regards,
>>>>> > Stevo.
>>>>> >
>>>>> > 2012/1/15 Tatsuo Ishii <ishii at postgresql.org>
>>>>> >
>>>>> >> fail_over_on_backend_error has different meaning from
>>>>> >> DISALLOW_TO_FAILOVER. From the doc:
>>>>> >>
>>>>> >>  If true, and an error occurs when writing to the backend
>>>>> >>  communication, pgpool-II will trigger the fail over procedure .
>>>>> This
>>>>> >>  is the same behavior as of pgpool-II 2.2.x or earlier. If set to
>>>>> >>  false, pgpool will report an error and disconnect the session.
>>>>> >>
>>>>> >> This means that if pgpool failed to read from backend, it will
>>>>> trigger
>>>>> >> failover even if fail_over_on_backend_error to off. So
>>>>> unconditionaly
>>>>> >> disabling failover will lead backward imcompatibilty.
>>>>> >>
>>>>> >> However I think we should disable failover if DISALLOW_TO_FAILOVER
>>>>> set
>>>>> >> in case of reading data from backend. This should have been done
>>>>> when
>>>>> >> DISALLOW_TO_FAILOVER was introduced because this is exactly what
>>>>> >> DISALLOW_TO_FAILOVER tries to accomplish. What do you think?
>>>>> >> --
>>>>> >> Tatsuo Ishii
>>>>> >> SRA OSS, Inc. Japan
>>>>> >> English: http://www.sraoss.co.jp/index_en.php
>>>>> >> Japanese: http://www.sraoss.co.jp
>>>>> >>
>>>>> >> > For a moment I thought we could have set
>>>>> fail_over_on_backend_error to
>>>>> >> off,
>>>>> >> > and have backends set with ALLOW_TO_FAILOVER flag. But then I
>>>>> looked in
>>>>> >> > code.
>>>>> >> >
>>>>> >> > In child.c there is a loop child process goes through in its
>>>>> lifetime.
>>>>> >> When
>>>>> >> > fatal error condition occurs before child process exits it will
>>>>> call
>>>>> >> > notice_backend_error which will call degenerate_backend_set which
>>>>> will
>>>>> >> not
>>>>> >> > take into account fail_over_on_backend_error is set to off,
>>>>> causing
>>>>> >> backend
>>>>> >> > to be degenerated and failover to occur. That's why we have
>>>>> backends set
>>>>> >> > with DISALLOW_TO_FAILOVER but with our patch applied, health
>>>>> check could
>>>>> >> > cause failover to occur as expected.
>>>>> >> >
>>>>> >> > Maybe it would be enough just to modify degenerate_backend_set,
>>>>> to take
>>>>> >> > fail_over_on_backend_error into account just like it already takes
>>>>> >> > DISALLOW_TO_FAILOVER into account.
>>>>> >> >
>>>>> >> > Kind regards,
>>>>> >> > Stevo.
>>>>> >> >
>>>>> >> > 2012/1/15 Stevo Slavić <sslavic at gmail.com>
>>>>> >> >
>>>>> >> >> Yes and that behaviour which you describe as expected, is not
>>>>> what we
>>>>> >> >> want. We want pgpool to degrade backend0 and failover when
>>>>> configured
>>>>> >> max
>>>>> >> >> health check retries have failed, and to failover only in that
>>>>> case, so
>>>>> >> not
>>>>> >> >> sooner e.g. connection/child error condition, but as soon as max
>>>>> health
>>>>> >> >> check retries have been attempted.
>>>>> >> >>
>>>>> >> >> Maybe examples will be more clear.
>>>>> >> >>
>>>>> >> >> Imagine two nodes (node 1 and node 2). On each node a single
>>>>> pgpool and
>>>>> >> a
>>>>> >> >> single backend. Apps/clients access db through pgpool on their
>>>>> own node.
>>>>> >> >> Two backends are configured in postgres native streaming
>>>>> replication.
>>>>> >> >> pgpools are used in raw mode. Both pgpools have same backend as
>>>>> >> backend0,
>>>>> >> >> and same backend as backend1.
>>>>> >> >> initial state: both backends are up and pgpool can access them,
>>>>> clients
>>>>> >> >> connect to their pgpool and do their work on master backend,
>>>>> backend0.
>>>>> >> >>
>>>>> >> >> 1st case: unmodified/non-patched pgpool 3.1.1 is used, backends
>>>>> are
>>>>> >> >> configured with ALLOW_TO_FAILOVER flag
>>>>> >> >> - temporary network outage happens between pgpool on node 2 and
>>>>> backend0
>>>>> >> >> - error condition is reported by child process, and since
>>>>> >> >> ALLOW_TO_FAILOVER is set, pgpool performs failover without giving
>>>>> >> chance to
>>>>> >> >> pgpool health check retries to control whether backend is just
>>>>> >> temporarily
>>>>> >> >> inaccessible
>>>>> >> >> - failover command on node 2 promotes standby backend to a new
>>>>> master -
>>>>> >> >> split brain occurs, with two masters
>>>>> >> >>
>>>>> >> >>
>>>>> >> >> 2nd case: unmodified/non-patched pgpool 3.1.1 is used, backends
>>>>> are
>>>>> >> >> configured with DISALLOW_TO_FAILOVER
>>>>> >> >> - temporary network outage happens between pgpool on node 2 and
>>>>> backend0
>>>>> >> >> - error condition is reported by child process, and since
>>>>> >> >> DISALLOW_TO_FAILOVER is set, pgpool does not perform failover
>>>>> >> >> - health check gets a chance to check backend0 condition,
>>>>> determines
>>>>> >> that
>>>>> >> >> it's not accessible, there will be no health check retries
>>>>> because
>>>>> >> >> DISALLOW_TO_FAILOVER is set, no failover occurs ever
>>>>> >> >>
>>>>> >> >>
>>>>> >> >> 3rd case, pgpool 3.1.1 + patch you've sent applied, and backends
>>>>> >> >> configured with DISALLOW_TO_FAILOVER
>>>>> >> >> - temporary network outage happens between pgpool on node 2 and
>>>>> backend0
>>>>> >> >> - error condition is reported by child process, and since
>>>>> >> >> DISALLOW_TO_FAILOVER is set, pgpool does not perform failover
>>>>> >> >> - health check gets a chance to check backend0 condition,
>>>>> determines
>>>>> >> that
>>>>> >> >> it's not accessible, health check retries happen, and even after
>>>>> max
>>>>> >> >> retries, no failover happens since failover is disallowed
>>>>> >> >>
>>>>> >> >>
>>>>> >> >> 4th expected behaviour, pgpool 3.1.1 + patch we sent, and
>>>>> backends
>>>>> >> >> configured with DISALLOW_TO_FAILOVER
>>>>> >> >> - temporary network outage happens between pgpool on node 2 and
>>>>> backend0
>>>>> >> >> - error condition is reported by child process, and since
>>>>> >> >> DISALLOW_TO_FAILOVER is set, pgpool does not perform failover
>>>>> >> >> - health check gets a chance to check backend0 condition,
>>>>> determines
>>>>> >> that
>>>>> >> >> it's not accessible, health check retries happen, before a max
>>>>> retry
>>>>> >> >> network condition is cleared, retry happens, and backend0
>>>>> remains to be
>>>>> >> >> master, no failover occurs, temporary network issue did not
>>>>> cause split
>>>>> >> >> brain
>>>>> >> >> - after some time, temporary network outage happens again
>>>>> between pgpool
>>>>> >> >> on node 2 and backend0
>>>>> >> >> - error condition is reported by child process, and since
>>>>> >> >> DISALLOW_TO_FAILOVER is set, pgpool does not perform failover
>>>>> >> >> - health check gets a chance to check backend0 condition,
>>>>> determines
>>>>> >> that
>>>>> >> >> it's not accessible, health check retries happen, after max
>>>>> retries
>>>>> >> >> backend0 is still not accessible, failover happens, standby is
>>>>> new
>>>>> >> master
>>>>> >> >> and backend0 is degraded
>>>>> >> >>
>>>>> >> >> Kind regards,
>>>>> >> >> Stevo.
>>>>> >> >>
>>>>> >> >>
>>>>> >> >> 2012/1/15 Tatsuo Ishii <ishii at postgresql.org>
>>>>> >> >>
>>>>> >> >>> In my test evironment, the patch works as expected. I have two
>>>>> >> >>> backends. Health check retry conf is as follows:
>>>>> >> >>>
>>>>> >> >>> health_check_max_retries = 3
>>>>> >> >>> health_check_retry_delay = 1
>>>>> >> >>>
>>>>> >> >>> 5 09:17:20 LOG:   pid 21411: Backend status file
>>>>> /home/t-ishii/work/
>>>>> >> >>> git.postgresql.org/test/log/pgpool_status discarded
>>>>> >> >>> 2012-01-15 09:17:20 LOG:   pid 21411: pgpool-II successfully
>>>>> started.
>>>>> >> >>> version 3.2alpha1 (hatsuiboshi)
>>>>> >> >>> 2012-01-15 09:17:20 LOG:   pid 21411: find_primary_node:
>>>>> primary node
>>>>> >> id
>>>>> >> >>> is 0
>>>>> >> >>> -- backend1 was shutdown
>>>>> >> >>>
>>>>> >> >>> 2012-01-15 09:17:50 ERROR: pid 21445:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:17:50 ERROR: pid 21445:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> 2012-01-15 09:17:50 ERROR: pid 21445:
>>>>> check_replication_time_lag: could
>>>>> >> >>> not connect to DB node 1, check sr_check_user and
>>>>> sr_check_password
>>>>> >> >>> 2012-01-15 09:17:50 ERROR: pid 21411:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:17:50 ERROR: pid 21411:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> 2012-01-15 09:17:50 ERROR: pid 21411:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:17:50 ERROR: pid 21411:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> -- health check failed
>>>>> >> >>>
>>>>> >> >>> 2012-01-15 09:17:50 ERROR: pid 21411: health check failed. 1 th
>>>>> host
>>>>> >> /tmp
>>>>> >> >>> at port 11001 is down
>>>>> >> >>> -- start retrying
>>>>> >> >>> 2012-01-15 09:17:50 LOG:   pid 21411: health check retry sleep
>>>>> time: 1
>>>>> >> >>> second(s)
>>>>> >> >>> 2012-01-15 09:17:51 ERROR: pid 21411:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:17:51 ERROR: pid 21411:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> 2012-01-15 09:17:51 ERROR: pid 21411: health check failed. 1 th
>>>>> host
>>>>> >> /tmp
>>>>> >> >>> at port 11001 is down
>>>>> >> >>> 2012-01-15 09:17:51 LOG:   pid 21411: health check retry sleep
>>>>> time: 1
>>>>> >> >>> second(s)
>>>>> >> >>> 2012-01-15 09:17:52 ERROR: pid 21411:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:17:52 ERROR: pid 21411:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> 2012-01-15 09:17:52 ERROR: pid 21411: health check failed. 1 th
>>>>> host
>>>>> >> /tmp
>>>>> >> >>> at port 11001 is down
>>>>> >> >>> 2012-01-15 09:17:52 LOG:   pid 21411: health check retry sleep
>>>>> time: 1
>>>>> >> >>> second(s)
>>>>> >> >>> 2012-01-15 09:17:53 ERROR: pid 21411:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:17:53 ERROR: pid 21411:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> 2012-01-15 09:17:53 ERROR: pid 21411: health check failed. 1 th
>>>>> host
>>>>> >> /tmp
>>>>> >> >>> at port 11001 is down
>>>>> >> >>> 2012-01-15 09:17:53 LOG:   pid 21411: health_check: 1 failover
>>>>> is
>>>>> >> canceld
>>>>> >> >>> because failover is disallowed
>>>>> >> >>> -- after 3 retries, pgpool wanted to failover, but gave up
>>>>> because
>>>>> >> >>> DISALLOW_TO_FAILOVER is set for backend1
>>>>> >> >>>
>>>>> >> >>> 2012-01-15 09:18:00 ERROR: pid 21445:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:18:00 ERROR: pid 21445:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> 2012-01-15 09:18:00 ERROR: pid 21445:
>>>>> check_replication_time_lag: could
>>>>> >> >>> not connect to DB node 1, check sr_check_user and
>>>>> sr_check_password
>>>>> >> >>> 2012-01-15 09:18:03 ERROR: pid 21411:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:18:03 ERROR: pid 21411:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> 2012-01-15 09:18:03 ERROR: pid 21411: health check failed. 1 th
>>>>> host
>>>>> >> /tmp
>>>>> >> >>> at port 11001 is down
>>>>> >> >>> 2012-01-15 09:18:03 LOG:   pid 21411: health check retry sleep
>>>>> time: 1
>>>>> >> >>> second(s)
>>>>> >> >>> 2012-01-15 09:18:04 ERROR: pid 21411:
>>>>> >> connect_unix_domain_socket_by_port:
>>>>> >> >>> connect() failed to /tmp/.s.PGSQL.11001: No such file or
>>>>> directory
>>>>> >> >>> 2012-01-15 09:18:04 ERROR: pid 21411:
>>>>> make_persistent_db_connection:
>>>>> >> >>> connection to /tmp(11001) failed
>>>>> >> >>> 2012-01-15 09:18:04 ERROR: pid 21411: health check failed. 1 th
>>>>> host
>>>>> >> /tmp
>>>>> >> >>> at port 11001 is down
>>>>> >> >>> 2012-01-15 09:18:04 LOG:   pid 21411: health check retry sleep
>>>>> time: 1
>>>>> >> >>> second(s)
>>>>> >> >>> 2012-01-15 09:18:05 LOG:   pid 21411: after some retrying
>>>>> backend
>>>>> >> >>> returned to healthy state
>>>>> >> >>> -- started backend1 and pgpool succeeded in health checking.
>>>>> Resumed
>>>>> >> >>> using backend1
>>>>> >> >>> --
>>>>> >> >>> Tatsuo Ishii
>>>>> >> >>> SRA OSS, Inc. Japan
>>>>> >> >>> English: http://www.sraoss.co.jp/index_en.php
>>>>> >> >>> Japanese: http://www.sraoss.co.jp
>>>>> >> >>>
>>>>> >> >>> > Hello Tatsuo,
>>>>> >> >>> >
>>>>> >> >>> > Thank you for the patch and effort, but unfortunately this
>>>>> change
>>>>> >> won't
>>>>> >> >>> > work for us. We need to set disallow failover to prevent
>>>>> failover on
>>>>> >> >>> child
>>>>> >> >>> > reported connection errors (it's ok if few clients lose their
>>>>> >> >>> connection or
>>>>> >> >>> > can not connect), and still have pgpool perform failover but
>>>>> only on
>>>>> >> >>> failed
>>>>> >> >>> > health check (if configured, after max retries threshold has
>>>>> been
>>>>> >> >>> reached).
>>>>> >> >>> >
>>>>> >> >>> > Maybe it would be best to add an extra value for backend_flag
>>>>> -
>>>>> >> >>> > ALLOW_TO_FAILOVER_ON_HEALTH_CHECK or
>>>>> >> >>> DISALLOW_TO_FAILOVER_ON_CHILD_ERROR.
>>>>> >> >>> > It should behave same as DISALLOW_TO_FAILOVER is set, with
>>>>> only
>>>>> >> >>> difference
>>>>> >> >>> > in behaviour when health check (if set, max retries) has
>>>>> failed -
>>>>> >> unlike
>>>>> >> >>> > DISALLOW_TO_FAILOVER, this new flag should allow failover in
>>>>> this
>>>>> >> case
>>>>> >> >>> only.
>>>>> >> >>> >
>>>>> >> >>> > Without this change health check (especially health check
>>>>> retries)
>>>>> >> >>> doesn't
>>>>> >> >>> > make much sense - child error is more likely to occur on
>>>>> (temporary)
>>>>> >> >>> > backend failure then health check and will or will not cause
>>>>> >> failover to
>>>>> >> >>> > occur depending on backend flag, without giving health check
>>>>> retries
>>>>> >> a
>>>>> >> >>> > chance to determine if failure was temporary or not, risking
>>>>> split
>>>>> >> brain
>>>>> >> >>> > situation with two masters just because of temporary network
>>>>> link
>>>>> >> >>> hiccup.
>>>>> >> >>> >
>>>>> >> >>> > Our main problem remains though with the health check timeout
>>>>> not
>>>>> >> being
>>>>> >> >>> > respected in these special conditions we have. Maybe Nenad
>>>>> can help
>>>>> >> you
>>>>> >> >>> > more to reproduce the issue on your environment.
>>>>> >> >>> >
>>>>> >> >>> > Kind regards,
>>>>> >> >>> > Stevo.
>>>>> >> >>> >
>>>>> >> >>> > 2012/1/13 Tatsuo Ishii <ishii at postgresql.org>
>>>>> >> >>> >
>>>>> >> >>> >> Thanks for pointing it out.
>>>>> >> >>> >> Yes, checking DISALLOW_TO_FAILOVER before retrying is wrong.
>>>>> >> >>> >> However, after retry count over, we should check
>>>>> >> DISALLOW_TO_FAILOVER I
>>>>> >> >>> >> think.
>>>>> >> >>> >> Attached is the patch attempt to fix it. Please try.
>>>>> >> >>> >> --
>>>>> >> >>> >> Tatsuo Ishii
>>>>> >> >>> >> SRA OSS, Inc. Japan
>>>>> >> >>> >> English: http://www.sraoss.co.jp/index_en.php
>>>>> >> >>> >> Japanese: http://www.sraoss.co.jp
>>>>> >> >>> >>
>>>>> >> >>> >> > pgpool is being used in raw mode - just for (health check
>>>>> based)
>>>>> >> >>> failover
>>>>> >> >>> >> > part, so applications are not required to restart when
>>>>> standby
>>>>> >> gets
>>>>> >> >>> >> > promoted to new master. Here is pgpool.conf file and a
>>>>> very small
>>>>> >> >>> patch
>>>>> >> >>> >> > we're using applied to pgpool 3.1.1 release.
>>>>> >> >>> >> >
>>>>> >> >>> >> > We have to have DISALLOW_TO_FAILOVER set for the backend
>>>>> since any
>>>>> >> >>> child
>>>>> >> >>> >> > process that detects condition that master/backend0 is not
>>>>> >> >>> available, if
>>>>> >> >>> >> > DISALLOW_TO_FAILOVER was not set, will degenerate backend
>>>>> without
>>>>> >> >>> giving
>>>>> >> >>> >> > health check a chance to retry. We need health check with
>>>>> retries
>>>>> >> >>> because
>>>>> >> >>> >> > condition that backend0 is not available could be temporary
>>>>> >> (network
>>>>> >> >>> >> > glitches to the remote site where master is, or deliberate
>>>>> >> failover
>>>>> >> >>> of
>>>>> >> >>> >> > master postgres service from one node to the other on
>>>>> remote site
>>>>> >> -
>>>>> >> >>> in
>>>>> >> >>> >> both
>>>>> >> >>> >> > cases remote means remote to the pgpool that is going to
>>>>> perform
>>>>> >> >>> health
>>>>> >> >>> >> > checks and ultimately the failover) and we don't want
>>>>> standby to
>>>>> >> be
>>>>> >> >>> >> > promoted as easily to a new master, to prevent temporary
>>>>> network
>>>>> >> >>> >> conditions
>>>>> >> >>> >> > which could occur frequently to frequently cause split
>>>>> brain with
>>>>> >> two
>>>>> >> >>> >> > masters.
>>>>> >> >>> >> >
>>>>> >> >>> >> > But then, with DISALLOW_TO_FAILOVER set, without the patch
>>>>> health
>>>>> >> >>> check
>>>>> >> >>> >> > will not retry and will thus give only one chance to
>>>>> backend (if
>>>>> >> >>> health
>>>>> >> >>> >> > check ever occurs before child process failure to connect
>>>>> to the
>>>>> >> >>> >> backend),
>>>>> >> >>> >> > rendering retry settings effectively to be ignored. That's
>>>>> where
>>>>> >> this
>>>>> >> >>> >> patch
>>>>> >> >>> >> > comes into action - enables health check retries while
>>>>> child
>>>>> >> >>> processes
>>>>> >> >>> >> are
>>>>> >> >>> >> > prevented to degenerate backend.
>>>>> >> >>> >> >
>>>>> >> >>> >> > I don't think, but I could be wrong, that this patch
>>>>> influences
>>>>> >> the
>>>>> >> >>> >> > behavior we're seeing with unwanted health check attempt
>>>>> delays.
>>>>> >> >>> Also,
>>>>> >> >>> >> > knowing this, maybe pgpool could be patched or some other
>>>>> support
>>>>> >> be
>>>>> >> >>> >> built
>>>>> >> >>> >> > into it to cover this use case.
>>>>> >> >>> >> >
>>>>> >> >>> >> > Regards,
>>>>> >> >>> >> > Stevo.
>>>>> >> >>> >> >
>>>>> >> >>> >> >
>>>>> >> >>> >> > 2012/1/12 Tatsuo Ishii <ishii at postgresql.org>
>>>>> >> >>> >> >
>>>>> >> >>> >> >> I have accepted the moderation request. Your post should
>>>>> be sent
>>>>> >> >>> >> shortly.
>>>>> >> >>> >> >> Also I have raised the post size limit to 1MB.
>>>>> >> >>> >> >> I will look into this...
>>>>> >> >>> >> >> --
>>>>> >> >>> >> >> Tatsuo Ishii
>>>>> >> >>> >> >> SRA OSS, Inc. Japan
>>>>> >> >>> >> >> English: http://www.sraoss.co.jp/index_en.php
>>>>> >> >>> >> >> Japanese: http://www.sraoss.co.jp
>>>>> >> >>> >> >>
>>>>> >> >>> >> >> > Here is the log file and strace output file (this time
>>>>> in an
>>>>> >> >>> archive,
>>>>> >> >>> >> >> > didn't know about 200KB constraint on post size which
>>>>> requires
>>>>> >> >>> >> moderator
>>>>> >> >>> >> >> > approval). Timings configured are 30sec health check
>>>>> interval,
>>>>> >> >>> 5sec
>>>>> >> >>> >> >> > timeout, and 2 retries with 10sec retry delay.
>>>>> >> >>> >> >> >
>>>>> >> >>> >> >> > It takes a lot more than 5sec from started health check
>>>>> to
>>>>> >> >>> sleeping
>>>>> >> >>> >> 10sec
>>>>> >> >>> >> >> > for first retry.
>>>>> >> >>> >> >> >
>>>>> >> >>> >> >> > Seen in code (main.x, health_check() function), within
>>>>> (retry)
>>>>> >> >>> attempt
>>>>> >> >>> >> >> > there is inner retry (first with postgres database then
>>>>> with
>>>>> >> >>> >> template1)
>>>>> >> >>> >> >> and
>>>>> >> >>> >> >> > that part doesn't seem to be interrupted by alarm.
>>>>> >> >>> >> >> >
>>>>> >> >>> >> >> > Regards,
>>>>> >> >>> >> >> > Stevo.
>>>>> >> >>> >> >> >
>>>>> >> >>> >> >> > 2012/1/12 Stevo Slavić <sslavic at gmail.com>
>>>>> >> >>> >> >> >
>>>>> >> >>> >> >> >> Here is the log file and strace output file. Timings
>>>>> >> configured
>>>>> >> >>> are
>>>>> >> >>> >> >> 30sec
>>>>> >> >>> >> >> >> health check interval, 5sec timeout, and 2 retries
>>>>> with 10sec
>>>>> >> >>> retry
>>>>> >> >>> >> >> delay.
>>>>> >> >>> >> >> >>
>>>>> >> >>> >> >> >> It takes a lot more than 5sec from started health
>>>>> check to
>>>>> >> >>> sleeping
>>>>> >> >>> >> >> 10sec
>>>>> >> >>> >> >> >> for first retry.
>>>>> >> >>> >> >> >>
>>>>> >> >>> >> >> >> Seen in code (main.x, health_check() function), within
>>>>> (retry)
>>>>> >> >>> >> attempt
>>>>> >> >>> >> >> >> there is inner retry (first with postgres database
>>>>> then with
>>>>> >> >>> >> template1)
>>>>> >> >>> >> >> and
>>>>> >> >>> >> >> >> that part doesn't seem to be interrupted by alarm.
>>>>> >> >>> >> >> >>
>>>>> >> >>> >> >> >> Regards,
>>>>> >> >>> >> >> >> Stevo.
>>>>> >> >>> >> >> >>
>>>>> >> >>> >> >> >>
>>>>> >> >>> >> >> >> 2012/1/11 Tatsuo Ishii <ishii at postgresql.org>
>>>>> >> >>> >> >> >>
>>>>> >> >>> >> >> >>> Ok, I will do it. In the mean time you could use
>>>>> "strace -tt
>>>>> >> -p
>>>>> >> >>> PID"
>>>>> >> >>> >> >> >>> to see which system call is blocked.
>>>>> >> >>> >> >> >>> --
>>>>> >> >>> >> >> >>> Tatsuo Ishii
>>>>> >> >>> >> >> >>> SRA OSS, Inc. Japan
>>>>> >> >>> >> >> >>> English: http://www.sraoss.co.jp/index_en.php
>>>>> >> >>> >> >> >>> Japanese: http://www.sraoss.co.jp
>>>>> >> >>> >> >> >>>
>>>>> >> >>> >> >> >>> > OK, got the info - key point is that ip forwarding
>>>>> is
>>>>> >> >>> disabled for
>>>>> >> >>> >> >> >>> security
>>>>> >> >>> >> >> >>> > reasons. Rules in iptables are not important,
>>>>> iptables can
>>>>> >> be
>>>>> >> >>> >> >> stopped,
>>>>> >> >>> >> >> >>> or
>>>>> >> >>> >> >> >>> > previously added rules removed.
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> > Here are the steps to reproduce (kudos to my
>>>>> colleague
>>>>> >> Nenad
>>>>> >> >>> >> >> Bulatovic
>>>>> >> >>> >> >> >>> for
>>>>> >> >>> >> >> >>> > providing this):
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> > 1.) make sure that ip forwarding is off:
>>>>> >> >>> >> >> >>> >     echo 0 > /proc/sys/net/ipv4/ip_forward
>>>>> >> >>> >> >> >>> > 2.) create IP alias on some interface (and have
>>>>> postgres
>>>>> >> >>> listen on
>>>>> >> >>> >> >> it):
>>>>> >> >>> >> >> >>> >     ip addr add x.x.x.x/yy dev ethz
>>>>> >> >>> >> >> >>> > 3.) set backend_hostname0 to aforementioned IP
>>>>> >> >>> >> >> >>> > 4.) start pgpool and monitor health checks
>>>>> >> >>> >> >> >>> > 5.) remove IP alias:
>>>>> >> >>> >> >> >>> >     ip addr del x.x.x.x/yy dev ethz
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> > Here is the interesting part in pgpool log after
>>>>> this:
>>>>> >> >>> >> >> >>> > 2012-01-11 17:38:04 DEBUG: pid 24358: starting
>>>>> health
>>>>> >> checking
>>>>> >> >>> >> >> >>> > 2012-01-11 17:38:04 DEBUG: pid 24358: health_check:
>>>>> 0 th DB
>>>>> >> >>> node
>>>>> >> >>> >> >> >>> status: 2
>>>>> >> >>> >> >> >>> > 2012-01-11 17:38:04 DEBUG: pid 24358: health_check:
>>>>> 1 th DB
>>>>> >> >>> node
>>>>> >> >>> >> >> >>> status: 1
>>>>> >> >>> >> >> >>> > 2012-01-11 17:38:34 DEBUG: pid 24358: starting
>>>>> health
>>>>> >> checking
>>>>> >> >>> >> >> >>> > 2012-01-11 17:38:34 DEBUG: pid 24358: health_check:
>>>>> 0 th DB
>>>>> >> >>> node
>>>>> >> >>> >> >> >>> status: 2
>>>>> >> >>> >> >> >>> > 2012-01-11 17:41:43 DEBUG: pid 24358: health_check:
>>>>> 0 th DB
>>>>> >> >>> node
>>>>> >> >>> >> >> >>> status: 2
>>>>> >> >>> >> >> >>> > 2012-01-11 17:41:46 ERROR: pid 24358: health check
>>>>> failed.
>>>>> >> 0
>>>>> >> >>> th
>>>>> >> >>> >> host
>>>>> >> >>> >> >> >>> > 192.168.2.27 at port 5432 is down
>>>>> >> >>> >> >> >>> > 2012-01-11 17:41:46 LOG:   pid 24358: health check
>>>>> retry
>>>>> >> sleep
>>>>> >> >>> >> time:
>>>>> >> >>> >> >> 10
>>>>> >> >>> >> >> >>> > second(s)
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> > That pgpool was configured with health check
>>>>> interval of
>>>>> >> >>> 30sec,
>>>>> >> >>> >> 5sec
>>>>> >> >>> >> >> >>> > timeout, and 10sec retry delay with 2 max retries.
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> > Making use of libpq instead for connecting to db in
>>>>> health
>>>>> >> >>> checks
>>>>> >> >>> >> IMO
>>>>> >> >>> >> >> >>> > should resolve it, but you'll best determine which
>>>>> call
>>>>> >> >>> exactly
>>>>> >> >>> >> gets
>>>>> >> >>> >> >> >>> > blocked waiting. Btw, psql with PGCONNECT_TIMEOUT
>>>>> env var
>>>>> >> >>> >> configured
>>>>> >> >>> >> >> >>> > respects that env var timeout.
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> > Regards,
>>>>> >> >>> >> >> >>> > Stevo.
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> > On Wed, Jan 11, 2012 at 11:15 AM, Stevo Slavić <
>>>>> >> >>> sslavic at gmail.com
>>>>> >> >>> >> >
>>>>> >> >>> >> >> >>> wrote:
>>>>> >> >>> >> >> >>> >
>>>>> >> >>> >> >> >>> >> Tatsuo,
>>>>> >> >>> >> >> >>> >>
>>>>> >> >>> >> >> >>> >> Did you restart iptables after adding rule?
>>>>> >> >>> >> >> >>> >>
>>>>> >> >>> >> >> >>> >> Regards,
>>>>> >> >>> >> >> >>> >> Stevo.
>>>>> >> >>> >> >> >>> >>
>>>>> >> >>> >> >> >>> >>
>>>>> >> >>> >> >> >>> >> On Wed, Jan 11, 2012 at 11:12 AM, Stevo Slavić <
>>>>> >> >>> >> sslavic at gmail.com>
>>>>> >> >>> >> >> >>> wrote:
>>>>> >> >>> >> >> >>> >>
>>>>> >> >>> >> >> >>> >>> Looking into this to verify if these are all
>>>>> necessary
>>>>> >> >>> changes
>>>>> >> >>> >> to
>>>>> >> >>> >> >> have
>>>>> >> >>> >> >> >>> >>> port unreachable message silently rejected
>>>>> (suspecting
>>>>> >> some
>>>>> >> >>> >> kernel
>>>>> >> >>> >> >> >>> >>> parameter tuning is needed).
>>>>> >> >>> >> >> >>> >>>
>>>>> >> >>> >> >> >>> >>> Just to clarify it's not a problem that host is
>>>>> being
>>>>> >> >>> detected
>>>>> >> >>> >> by
>>>>> >> >>> >> >> >>> pgpool
>>>>> >> >>> >> >> >>> >>> to be down, but the timing when that happens. On
>>>>> >> environment
>>>>> >> >>> >> where
>>>>> >> >>> >> >> >>> issue is
>>>>> >> >>> >> >> >>> >>> reproduced pgpool as part of health check attempt
>>>>> tries
>>>>> >> to
>>>>> >> >>> >> connect
>>>>> >> >>> >> >> to
>>>>> >> >>> >> >> >>> >>> backend and hangs for tcp timeout instead of being
>>>>> >> >>> interrupted
>>>>> >> >>> >> by
>>>>> >> >>> >> >> >>> timeout
>>>>> >> >>> >> >> >>> >>> alarm. Can you verify/confirm please the health
>>>>> check
>>>>> >> retry
>>>>> >> >>> >> timings
>>>>> >> >>> >> >> >>> are not
>>>>> >> >>> >> >> >>> >>> delayed?
>>>>> >> >>> >> >> >>> >>>
>>>>> >> >>> >> >> >>> >>> Regards,
>>>>> >> >>> >> >> >>> >>> Stevo.
>>>>> >> >>> >> >> >>> >>>
>>>>> >> >>> >> >> >>> >>>
>>>>> >> >>> >> >> >>> >>> On Wed, Jan 11, 2012 at 10:50 AM, Tatsuo Ishii <
>>>>> >> >>> >> >> ishii at postgresql.org
>>>>> >> >>> >> >> >>> >wrote:
>>>>> >> >>> >> >> >>> >>>
>>>>> >> >>> >> >> >>> >>>> Ok, I did:
>>>>> >> >>> >> >> >>> >>>>
>>>>> >> >>> >> >> >>> >>>> # iptables -A FORWARD -j REJECT --reject-with
>>>>> >> >>> >> >> icmp-port-unreachable
>>>>> >> >>> >> >> >>> >>>>
>>>>> >> >>> >> >> >>> >>>> on the host where pgpoo is running. And pull
>>>>> network
>>>>> >> cable
>>>>> >> >>> from
>>>>> >> >>> >> >> >>> >>>> backend0 host network interface. Pgpool detected
>>>>> the
>>>>> >> host
>>>>> >> >>> being
>>>>> >> >>> >> >> down
>>>>> >> >>> >> >> >>> >>>> as expected...
>>>>> >> >>> >> >> >>> >>>> --
>>>>> >> >>> >> >> >>> >>>> Tatsuo Ishii
>>>>> >> >>> >> >> >>> >>>> SRA OSS, Inc. Japan
>>>>> >> >>> >> >> >>> >>>> English: http://www.sraoss.co.jp/index_en.php
>>>>> >> >>> >> >> >>> >>>> Japanese: http://www.sraoss.co.jp
>>>>> >> >>> >> >> >>> >>>>
>>>>> >> >>> >> >> >>> >>>> > Backend is not destination of this message,
>>>>> pgpool
>>>>> >> host
>>>>> >> >>> is,
>>>>> >> >>> >> and
>>>>> >> >>> >> >> we
>>>>> >> >>> >> >> >>> >>>> don't
>>>>> >> >>> >> >> >>> >>>> > want it to ever get it. With command I've sent
>>>>> you
>>>>> >> rule
>>>>> >> >>> will
>>>>> >> >>> >> be
>>>>> >> >>> >> >> >>> >>>> created for
>>>>> >> >>> >> >> >>> >>>> > any source and destination.
>>>>> >> >>> >> >> >>> >>>> >
>>>>> >> >>> >> >> >>> >>>> > Regards,
>>>>> >> >>> >> >> >>> >>>> > Stevo.
>>>>> >> >>> >> >> >>> >>>> >
>>>>> >> >>> >> >> >>> >>>> > On Wed, Jan 11, 2012 at 10:38 AM, Tatsuo Ishii
>>>>> <
>>>>> >> >>> >> >> >>> ishii at postgresql.org>
>>>>> >> >>> >> >> >>> >>>> wrote:
>>>>> >> >>> >> >> >>> >>>> >
>>>>> >> >>> >> >> >>> >>>> >> I did following:
>>>>> >> >>> >> >> >>> >>>> >>
>>>>> >> >>> >> >> >>> >>>> >> Do following on the host where pgpool is
>>>>> running on:
>>>>> >> >>> >> >> >>> >>>> >>
>>>>> >> >>> >> >> >>> >>>> >> # iptables -A FORWARD -j REJECT --reject-with
>>>>> >> >>> >> >> >>> icmp-port-unreachable -d
>>>>> >> >>> >> >> >>> >>>> >> 133.137.177.124
>>>>> >> >>> >> >> >>> >>>> >> (133.137.177.124 is the host where backend is
>>>>> running
>>>>> >> >>> on)
>>>>> >> >>> >> >> >>> >>>> >>
>>>>> >> >>> >> >> >>> >>>> >> Pull network cable from backend0 host network
>>>>> >> interface.
>>>>> >> >>> >> Pgpool
>>>>> >> >>> >> >> >>> >>>> >> detected the host being down as expected. Am I
>>>>> >> missing
>>>>> >> >>> >> >> something?
>>>>> >> >>> >> >> >>> >>>> >> --
>>>>> >> >>> >> >> >>> >>>> >> Tatsuo Ishii
>>>>> >> >>> >> >> >>> >>>> >> SRA OSS, Inc. Japan
>>>>> >> >>> >> >> >>> >>>> >> English: http://www.sraoss.co.jp/index_en.php
>>>>> >> >>> >> >> >>> >>>> >> Japanese: http://www.sraoss.co.jp
>>>>> >> >>> >> >> >>> >>>> >>
>>>>> >> >>> >> >> >>> >>>> >> > Hello Tatsuo,
>>>>> >> >>> >> >> >>> >>>> >> >
>>>>> >> >>> >> >> >>> >>>> >> > With backend0 on one host just configure
>>>>> following
>>>>> >> >>> rule on
>>>>> >> >>> >> >> other
>>>>> >> >>> >> >> >>> >>>> host
>>>>> >> >>> >> >> >>> >>>> >> where
>>>>> >> >>> >> >> >>> >>>> >> > pgpool is:
>>>>> >> >>> >> >> >>> >>>> >> >
>>>>> >> >>> >> >> >>> >>>> >> > iptables -A FORWARD -j REJECT --reject-with
>>>>> >> >>> >> >> >>> icmp-port-unreachable
>>>>> >> >>> >> >> >>> >>>> >> >
>>>>> >> >>> >> >> >>> >>>> >> > and then have pgpool startup with health
>>>>> checking
>>>>> >> and
>>>>> >> >>> >> >> retrying
>>>>> >> >>> >> >> >>> >>>> >> configured,
>>>>> >> >>> >> >> >>> >>>> >> > and then pull network cable from backend0
>>>>> host
>>>>> >> network
>>>>> >> >>> >> >> >>> interface.
>>>>> >> >>> >> >> >>> >>>> >> >
>>>>> >> >>> >> >> >>> >>>> >> > Regards,
>>>>> >> >>> >> >> >>> >>>> >> > Stevo.
>>>>> >> >>> >> >> >>> >>>> >> >
>>>>> >> >>> >> >> >>> >>>> >> > On Wed, Jan 11, 2012 at 6:27 AM, Tatsuo
>>>>> Ishii <
>>>>> >> >>> >> >> >>> ishii at postgresql.org
>>>>> >> >>> >> >> >>> >>>> >
>>>>> >> >>> >> >> >>> >>>> >> wrote:
>>>>> >> >>> >> >> >>> >>>> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> I want to try to test the situation you
>>>>> descrived:
>>>>> >> >>> >> >> >>> >>>> >> >>
>>>>> >> >>> >> >> >>> >>>> >> >> >> > When system is configured for security
>>>>> >> reasons
>>>>> >> >>> not
>>>>> >> >>> >> to
>>>>> >> >>> >> >> >>> return
>>>>> >> >>> >> >> >>> >>>> >> >> destination
>>>>> >> >>> >> >> >>> >>>> >> >> >> > host unreachable messages, even though
>>>>> >> >>> >> >> >>> health_check_timeout is
>>>>> >> >>> >> >> >>> >>>> >> >>
>>>>> >> >>> >> >> >>> >>>> >> >> But I don't know how to do it. I pulled
>>>>> out the
>>>>> >> >>> network
>>>>> >> >>> >> >> cable
>>>>> >> >>> >> >> >>> and
>>>>> >> >>> >> >> >>> >>>> >> >> pgpool detected it as expected. Also I
>>>>> configured
>>>>> >> the
>>>>> >> >>> >> server
>>>>> >> >>> >> >> >>> which
>>>>> >> >>> >> >> >>> >>>> >> >> PostgreSQL is running on to disable the
>>>>> 5432
>>>>> >> port. In
>>>>> >> >>> >> this
>>>>> >> >>> >> >> case
>>>>> >> >>> >> >> >>> >>>> >> >> connect(2) returned EHOSTUNREACH (No route
>>>>> to
>>>>> >> host)
>>>>> >> >>> so
>>>>> >> >>> >> >> pgpool
>>>>> >> >>> >> >> >>> >>>> detected
>>>>> >> >>> >> >> >>> >>>> >> >> the error as expected.
>>>>> >> >>> >> >> >>> >>>> >> >>
>>>>> >> >>> >> >> >>> >>>> >> >> Could you please instruct me?
>>>>> >> >>> >> >> >>> >>>> >> >> --
>>>>> >> >>> >> >> >>> >>>> >> >> Tatsuo Ishii
>>>>> >> >>> >> >> >>> >>>> >> >> SRA OSS, Inc. Japan
>>>>> >> >>> >> >> >>> >>>> >> >> English:
>>>>> http://www.sraoss.co.jp/index_en.php
>>>>> >> >>> >> >> >>> >>>> >> >> Japanese: http://www.sraoss.co.jp
>>>>> >> >>> >> >> >>> >>>> >> >>
>>>>> >> >>> >> >> >>> >>>> >> >> > Hello Tatsuo,
>>>>> >> >>> >> >> >>> >>>> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> > Thank you for replying!
>>>>> >> >>> >> >> >>> >>>> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> > I'm not sure what exactly is blocking,
>>>>> just by
>>>>> >> >>> pgpool
>>>>> >> >>> >> code
>>>>> >> >>> >> >> >>> >>>> analysis I
>>>>> >> >>> >> >> >>> >>>> >> >> > suspect it is the part where a
>>>>> connection is
>>>>> >> made
>>>>> >> >>> to
>>>>> >> >>> >> the
>>>>> >> >>> >> >> db
>>>>> >> >>> >> >> >>> and
>>>>> >> >>> >> >> >>> >>>> it
>>>>> >> >>> >> >> >>> >>>> >> >> doesn't
>>>>> >> >>> >> >> >>> >>>> >> >> > seem to get interrupted by alarm. Tested
>>>>> >> thoroughly
>>>>> >> >>> >> health
>>>>> >> >>> >> >> >>> check
>>>>> >> >>> >> >> >>> >>>> >> >> behaviour,
>>>>> >> >>> >> >> >>> >>>> >> >> > it works really well when host/ip is
>>>>> there and
>>>>> >> just
>>>>> >> >>> >> >> >>> >>>> backend/postgres
>>>>> >> >>> >> >> >>> >>>> >> is
>>>>> >> >>> >> >> >>> >>>> >> >> > down, but not when backend host/ip is
>>>>> down. I
>>>>> >> could
>>>>> >> >>> >> see in
>>>>> >> >>> >> >> >>> log
>>>>> >> >>> >> >> >>> >>>> that
>>>>> >> >>> >> >> >>> >>>> >> >> initial
>>>>> >> >>> >> >> >>> >>>> >> >> > health check and each retry got delayed
>>>>> when
>>>>> >> >>> host/ip is
>>>>> >> >>> >> >> not
>>>>> >> >>> >> >> >>> >>>> reachable,
>>>>> >> >>> >> >> >>> >>>> >> >> > while when just backend is not listening
>>>>> (is
>>>>> >> down)
>>>>> >> >>> on
>>>>> >> >>> >> the
>>>>> >> >>> >> >> >>> >>>> reachable
>>>>> >> >>> >> >> >>> >>>> >> >> host/ip
>>>>> >> >>> >> >> >>> >>>> >> >> > then initial health check and all
>>>>> retries are
>>>>> >> >>> exact to
>>>>> >> >>> >> the
>>>>> >> >>> >> >> >>> >>>> settings in
>>>>> >> >>> >> >> >>> >>>> >> >> > pgpool.conf.
>>>>> >> >>> >> >> >>> >>>> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> > PGCONNECT_TIMEOUT is listed as one of
>>>>> the libpq
>>>>> >> >>> >> >> environment
>>>>> >> >>> >> >> >>> >>>> variables
>>>>> >> >>> >> >> >>> >>>> >> in
>>>>> >> >>> >> >> >>> >>>> >> >> > the docs (see
>>>>> >> >>> >> >> >>> >>>> >> >>
>>>>> >> >>> >> http://www.postgresql.org/docs/9.1/static/libpq-envars.html)
>>>>> >> >>> >> >> >>> >>>> >> >> > There is equivalent parameter in libpq
>>>>> >> >>> >> PGconnectdbParams (
>>>>> >> >>> >> >> >>> see
>>>>> >> >>> >> >> >>> >>>> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >>
>>>>> >> >>> >> >> >>> >>>> >>
>>>>> >> >>> >> >> >>> >>>>
>>>>> >> >>> >> >> >>>
>>>>> >> >>> >> >>
>>>>> >> >>> >>
>>>>> >> >>>
>>>>> >>
>>>>> http://www.postgresql.org/docs/9.1/static/libpq-connect.html#LIBPQ-CONNECT-CONNECT-TIMEOUT
>>>>> >> >>> >> >> >>> >>>> >> >> )
>>>>> >> >>> >> >> >>> >>>> >> >> > At the beginning of that same page there
>>>>> are
>>>>> >> some
>>>>> >> >>> >> >> important
>>>>> >> >>> >> >> >>> >>>> infos on
>>>>> >> >>> >> >> >>> >>>> >> >> using
>>>>> >> >>> >> >> >>> >>>> >> >> > these functions.
>>>>> >> >>> >> >> >>> >>>> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> > psql respects PGCONNECT_TIMEOUT.
>>>>> >> >>> >> >> >>> >>>> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> > Regards,
>>>>> >> >>> >> >> >>> >>>> >> >> > Stevo.
>>>>> >> >>> >> >> >>> >>>> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> > On Wed, Jan 11, 2012 at 12:13 AM, Tatsuo
>>>>> Ishii <
>>>>> >> >>> >> >> >>> >>>> ishii at postgresql.org>
>>>>> >> >>> >> >> >>> >>>> >> >> wrote:
>>>>> >> >>> >> >> >>> >>>> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> >> > Hello pgpool community,
>>>>> >> >>> >> >> >>> >>>> >> >> >> >
>>>>> >> >>> >> >> >>> >>>> >> >> >> > When system is configured for security
>>>>> >> reasons
>>>>> >> >>> not
>>>>> >> >>> >> to
>>>>> >> >>> >> >> >>> return
>>>>> >> >>> >> >> >>> >>>> >> >> destination
>>>>> >> >>> >> >> >>> >>>> >> >> >> > host unreachable messages, even though
>>>>> >> >>> >> >> >>> health_check_timeout is
>>>>> >> >>> >> >> >>> >>>> >> >> >> configured,
>>>>> >> >>> >> >> >>> >>>> >> >> >> > socket call will block and alarm will
>>>>> not get
>>>>> >> >>> raised
>>>>> >> >>> >> >> >>> until TCP
>>>>> >> >>> >> >> >>> >>>> >> timeout
>>>>> >> >>> >> >> >>> >>>> >> >> >> > occurs.
>>>>> >> >>> >> >> >>> >>>> >> >> >>
>>>>> >> >>> >> >> >>> >>>> >> >> >> Interesting. So are you saying that
>>>>> read(2)
>>>>> >> >>> cannot be
>>>>> >> >>> >> >> >>> >>>> interrupted by
>>>>> >> >>> >> >> >>> >>>> >> >> >> alarm signal if the system is
>>>>> configured not to
>>>>> >> >>> return
>>>>> >> >>> >> >> >>> >>>> destination
>>>>> >> >>> >> >> >>> >>>> >> >> >> host unreachable message? Could you
>>>>> please
>>>>> >> guide
>>>>> >> >>> me
>>>>> >> >>> >> >> where I
>>>>> >> >>> >> >> >>> can
>>>>> >> >>> >> >> >>> >>>> get
>>>>> >> >>> >> >> >>> >>>> >> >> >> such that info? (I'm not a network
>>>>> expert).
>>>>> >> >>> >> >> >>> >>>> >> >> >>
>>>>> >> >>> >> >> >>> >>>> >> >> >> > Not a C programmer, found some info
>>>>> that
>>>>> >> select
>>>>> >> >>> call
>>>>> >> >>> >> >> >>> could be
>>>>> >> >>> >> >> >>> >>>> >> replace
>>>>> >> >>> >> >> >>> >>>> >> >> >> with
>>>>> >> >>> >> >> >>> >>>> >> >> >> > select/pselect calls. Maybe it would
>>>>> be best
>>>>> >> if
>>>>> >> >>> >> >> >>> >>>> PGCONNECT_TIMEOUT
>>>>> >> >>> >> >> >>> >>>> >> >> value
>>>>> >> >>> >> >> >>> >>>> >> >> >> > could be used here for connection
>>>>> timeout.
>>>>> >> >>> pgpool
>>>>> >> >>> >> has
>>>>> >> >>> >> >> >>> libpq as
>>>>> >> >>> >> >> >>> >>>> >> >> >> dependency,
>>>>> >> >>> >> >> >>> >>>> >> >> >> > why isn't it using libpq for the
>>>>> healthcheck
>>>>> >> db
>>>>> >> >>> >> connect
>>>>> >> >>> >> >> >>> >>>> calls, then
>>>>> >> >>> >> >> >>> >>>> >> >> >> > PGCONNECT_TIMEOUT would be applied?
>>>>> >> >>> >> >> >>> >>>> >> >> >>
>>>>> >> >>> >> >> >>> >>>> >> >> >> I don't think libpq uses select/pselect
>>>>> for
>>>>> >> >>> >> establishing
>>>>> >> >>> >> >> >>> >>>> connection,
>>>>> >> >>> >> >> >>> >>>> >> >> >> but using libpq instead of homebrew
>>>>> code seems
>>>>> >> to
>>>>> >> >>> be
>>>>> >> >>> >> an
>>>>> >> >>> >> >> >>> idea.
>>>>> >> >>> >> >> >>> >>>> Let me
>>>>> >> >>> >> >> >>> >>>> >> >> >> think about it.
>>>>> >> >>> >> >> >>> >>>> >> >> >>
>>>>> >> >>> >> >> >>> >>>> >> >> >> One question. Are you sure that libpq
>>>>> can deal
>>>>> >> >>> with
>>>>> >> >>> >> the
>>>>> >> >>> >> >> case
>>>>> >> >>> >> >> >>> >>>> (not to
>>>>> >> >>> >> >> >>> >>>> >> >> >> return destination host unreachable
>>>>> messages)
>>>>> >> by
>>>>> >> >>> using
>>>>> >> >>> >> >> >>> >>>> >> >> >> PGCONNECT_TIMEOUT?
>>>>> >> >>> >> >> >>> >>>> >> >> >> --
>>>>> >> >>> >> >> >>> >>>> >> >> >> 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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