[pgpool-general: 157] Re: Healthcheck timeout not always respected

Sun Jan 15 11:49:38 JST 2012

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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