[Pgpool-general] pcp_child: pcp_read() failed. reason: Success

Fri Nov 6 05:52:26 UTC 2009

> Actually I'm was running pgpool on db2 (backend_hostname1) and am now
> running it on db3 (backend_hostname2).
> I have actually suspected that pgpool might be opting for some sort of
> socket connection to the local instance of postgres instead of using the
> TCP/IP connection parameters in an effort to speed things up.
> 
> I have done my best to ensure that pgpool has completely separate socket
> directories but it wouldn't be hard for pgpool to find a local postgres
> socket if it wanted.  If I end up with another outage and this time db3 is
> the postgres instance that locks up, I'll be fairly certain that this is the
> problem but for the moment I can only speculate.
> 
> I'm assuming you're suggesting I set backend_hostname0 = '' because it is
> already weighted to 0.0 anyway?

No. Because I thought you are running pgpool on db1. '' means force
pgpool to use UNIX domain socket. So if you running pgpool on db3, you
could set:

backend_hostname2 = ''

> I have db1 (backend_hostname0) weighted to 0.0 in an effort to direct all
> selects to the two slave hosts (db2 and db3) but still benefit from pgpool
> intelligently sending writes to db1.
> db1 is the mammoth master host and needs all available i/o to deal with
> writes.
> My understanding is that this is how "master_slave_mode = true" works.
> Writes are always directed to backend_hostname0.
> 
> If I need to reevaluate that thinking, please advise but that has been
> working for me for months now.
> 
> thx
> -s
> 
> On Thu, Nov 5, 2009 at 9:26 PM, Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
> 
> > Besides the useless error message from pgp_child(it seems someone
> > believed that EOF will set some error number to the global errono
> > variable. I will fix this anyway.), for me it seems socket files are
> > going dead. I suspect some network stack bugs could cause this but I'm
> > not sure. One thing you might want to try is, changing this:
> >
> > backend_hostname0 = 'db1.xxx.xxx'
> >
> > to:
> >
> > backend_hostname0 = ''
> >
> > This will make pgpool to use UNIX domain socket for the communication
> > channel to PostgreSQL, rather than TCP/IP. It may or may not affect
> > the problem you have, since the network code in the kernel will be
> > different.
> >
> > (I assume you are running pgpool on db1.xxx.xxx)
> > --
> > Tatsuo Ishii
> > SRA OSS, Inc. Japan
> >
> > > Has anyone else run into this:
> > >
> > > My pgpool instance runs without problems for days on end and then
> > suddenly
> > > stops responding to all requests.
> > > At the same moment, one of my three backend db hosts becomes completely
> > > inaccessible.
> > > Pgpool will not respond to shutdown, or even kill and must be kill -9'd
> > > Once all pgpool processes are out of the way, the inaccessible postgres
> > > server once again becomes responsive.
> > > I restart pgpool and everything works properly for a few more days.
> > >
> > > At the moment the problem occurs, pgpool's log output, which typically
> > > consists of just connection logging, turns into a steady stream of this:
> > > Nov  5 11:33:18 src at obfuscated pgpool: 2009-11-05 11:33:18 ERROR: pid
> > 12811:
> > > pcp_child: pcp_read() failed. reason: Success
> > > These errors show up sporaticlly in my pgpool logs all the time but don't
> > > appear to have any adverse effects until the whole thing takes a dive.
> > > I would desperately like to know what this error message is trying to
> > tell
> > > me.
> > >
> > > I have not been able to correlate any given query/connection/process to
> > the
> > > timing of the outages.
> > > Sometimes they happens at peak usage periods, sometimes they happen in
> > the
> > > middle of the night.
> > >
> > > I experienced this problem using pgpool-II v1.3 and have recently
> > upgraded
> > > to pgpool-II v2.2.5 but am still seeing the same issue.
> > >
> > > It may be relevant to point out that I am running pgpool on one of the
> > > machines that is also acting as a postgres backend and it is always the
> > > postgres instance on the pgpool host that locks up.
> > > This morning I moved the pgpool instance onto another one of the postgres
> > > backend hosts in an effort to see if the cohabitation of pgpool and
> > postgres
> > > is causing problems or if there is simply an issue with that postres on
> > that
> > > host of if this is just a coincidence.
> > > I likely won't gain anything from this test for a day or more.
> > >
> > > Also relevant is that I am running mammoth replicator and am only using
> > > pgpool for connection load balancing and high availability.
> > >
> > > Below is my pgpool.conf.
> > >
> > > Any thoughts appreciated.
> > >
> > > -steve crandell
> > >
> > >
> > >
> > > f
> > >
> > > #
> > > # pgpool-II configuration file sample
> > > # $Header: /cvsroot/pgpool/pgpool-II/pgpool.conf.sample,v 1.4.2.3
> > > 2007/10/12 09:15:02 y-asaba Exp $
> > >
> > > # Host name or IP address to listen on: '*' for all, '' for no TCP/IP
> > > # connections
> > > #listen_addresses = 'localhost'
> > > listen_addresses = '10.xxx.xxx.xxx'
> > >
> > > # Port number for pgpool
> > > port = 5432
> > >
> > > # Port number for pgpool communication manager
> > > pcp_port = 9898
> > >
> > > # Unix domain socket path.  (The Debian package defaults to
> > > # /var/run/postgresql.)
> > > socket_dir = '/usr/local/pgpool'
> > >
> > > # Unix domain socket path for pgpool communication manager.
> > > pcp_socket_dir = '/usr/local/pgpool'
> > >
> > > # Unix domain socket path for the backend. Debian package defaults to
> > > /var/run/postgresql!
> > > backend_socket_dir = '/usr/local/pgpool'
> > >
> > > # pgpool communication manager timeout. 0 means no timeout, but
> > > strongly not recommended!
> > > pcp_timeout = 10
> > >
> > > # number of pre-forked child process
> > > num_init_children = 32
> > >
> > >
> > > # Number of connection pools allowed for a child process
> > > max_pool = 4
> > >
> > >
> > > # If idle for this many seconds, child exits.  0 means no timeout.
> > > child_life_time = 30
> > >
> > > # If idle for this many seconds, connection to PostgreSQL closes.
> > > # 0 means no timeout.
> > > #connection_life_time = 0
> > > connection_life_time = 30
> > >
> > > # If child_max_connections connections were received, child exits.
> > > # 0 means no exit.
> > > # change
> > > child_max_connections = 0
> > >
> > > # Maximum time in seconds to complete client authentication.
> > > # 0 means no timeout.
> > > authentication_timeout = 60
> > >
> > > # Logging directory (more accurately, the directory for the PID file)
> > > logdir = '/usr/local/pgpool'
> > >
> > > # Replication mode
> > > replication_mode = false
> > >
> > > # Set this to true if you want to avoid deadlock situations when
> > > # replication is enabled.  There will, however, be a noticable
> > performance
> > > # degradation.  A workaround is to set this to false and insert a
> > /*STRICT*/
> > > # comment at the beginning of the SQL command.
> > > replication_strict = false
> > >
> > > # When replication_strict is set to false, there will be a chance for
> > > # deadlocks.  Set this to nonzero (in milliseconds) to detect this
> > > # situation and resolve the deadlock by aborting current session.
> > > replication_timeout = 5000
> > >
> > > # Load balancing mode, i.e., all SELECTs except in a transaction block
> > > # are load balanced.  This is ignored if replication_mode is false.
> > > # change
> > > load_balance_mode = true
> > >
> > > # if there's a data mismatch between master and secondary
> > > # start degeneration to stop replication mode
> > > replication_stop_on_mismatch = false
> > >
> > > # If true, replicate SELECT statement when load balancing is disabled.
> > > # If false, it is only sent to the master node.
> > > # change
> > > replicate_select = true
> > >
> > > # Semicolon separated list of queries to be issued at the end of a
> > session
> > > reset_query_list = 'ABORT; RESET ALL; SET SESSION AUTHORIZATION DEFAULT'
> > >
> > > # If true print timestamp on each log line.
> > > print_timestamp = true
> > >
> > > # If true, operate in master/slave mode.
> > > # change
> > > master_slave_mode = true
> > >
> > > # If true, cache connection pool.
> > > connection_cache = false
> > >
> > > # Health check timeout.  0 means no timeout.
> > > health_check_timeout = 20
> > >
> > > # Health check period.  0 means no health check.
> > > health_check_period = 0
> > >
> > > # Health check user
> > > health_check_user = 'nobody'
> > >
> > > # If true, automatically lock table with INSERT statements to keep SERIAL
> > > # data consistency.  An /*INSERT LOCK*/ comment has the same effect.  A
> > > # /NO INSERT LOCK*/ comment disables the effect.
> > > insert_lock = false
> > >
> > > # If true, ignore leading white spaces of each query while pgpool judges
> > > # whether the query is a SELECT so that it can be load balanced.  This
> > > # is useful for certain APIs such as DBI/DBD which is known to adding an
> > > # extra leading white space.
> > > ignore_leading_white_space = false
> > >
> > > # If true, print all statements to the log.  Like the log_statement
> > option
> > > # to PostgreSQL, this allows for observing queries without engaging in
> > full
> > > # debugging.
> > > log_statement = false
> > >
> > > # If true, incoming connections will be printed to the log.
> > > # change
> > > log_connections = true
> > >
> > > # If true, hostname will be shown in ps status. Also shown in
> > > # connection log if log_connections = true.
> > > # Be warned that this feature will add overhead to look up hostname.
> > > log_hostname = false
> > >
> > > # if non 0, run in parallel query mode
> > > parallel_mode = false
> > >
> > > # if non 0, use query cache
> > > enable_query_cache = 0
> > >
> > > #set pgpool2 hostname
> > > pgpool2_hostname = ''
> > >
> > > # system DB info
> > > #system_db_hostname = 'localhost'
> > > #system_db_port = 5432
> > > #system_db_dbname = 'pgpool'
> > > #system_db_schema = 'pgpool_catalog'
> > > #system_db_user = 'pgpool'
> > > #system_db_password = ''
> > >
> > > # backend_hostname, backend_port, backend_weight
> > > # here are examples
> > > backend_hostname0 = 'db1.xxx.xxx'
> > > backend_port0 = 5433
> > > backend_weight0 = 0.0
> > >
> > > backend_hostname1 = 'db2.xxx.xxx'
> > > backend_port1 = 5433
> > > backend_weight1 = 0.4
> > >
> > > backend_hostname2 = 'db3.xxx.xxx'
> > > backend_port2 = 5433
> > > backend_weight2 = 0.6
> > >
> > >
> > >
> > > # - HBA -
> > >
> > > # If true, use pool_hba.conf for client authentication. In pgpool-II
> > > # 1.1, the default value is false. The default value will be true in
> > > # 1.2.
> > > enable_pool_hba = false
> >