[pgpool-general: 183] Re: Healthcheck timeout not always respected

Stevo Slavić sslavic at gmail.com
Fri Jan 20 06:53:59 JST 2012 

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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