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

Tue Nov 10 04:08:05 UTC 2009

I think this is normal. We can easyly reproduce your problem.

1) set num_init_children = 1

2) connect pgpool via psql

3) fire up more psql

4) psql(3) will be "freezed" until psql(2) disconnect session.

This behavior is perfectly expected one.

Is this what you meant?
--
Tatsuo Ishii
SRA OSS, Inc. Japan

> I've done extensive testing since my last message.
> The problem appears to be that I am getting more connections to pgpool than
> I have num_init_children.
> Per my tests, as soon as pgpool gets connection num_init_children + 1, it
> locks up and takes at least one of the backend nodes with it.
> 
> Can anyone else confirm this?
> I'd like to make sure it is not just my particular configuration causing the
> issue.
> 
> In the mean time I have simply increased the num_init_children parameter
> significantly in an effort to stay well ahead of the number of incoming
> connections and this appears to be working.
> 
> -s
> 
> On Sun, Nov 8, 2009 at 3:23 AM, Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
> 
> > I would like to know how  the condition of pgpool is. What does ps
> > show for pgpool processes? Even better, can you attach debugger to one
> > of pgpool process and get back trace?
> > --
> > Tatsuo Ishii
> > SRA OSS, Inc. Japan
> >
> > > I've tried setting the local backend_hostname = ''
> > > Same problems are occurring.
> > > Pgpool has actually failed something like 4 separate times today, all but
> > > one of them using this local socket configuration.
> > >
> > > Any other thoughts?
> > >
> > > thx
> > > -s
> > >
> > > On Thu, Nov 5, 2009 at 10:52 PM, Tatsuo Ishii <ishii at sraoss.co.jp>
> > wrote:
> > >
> > > > > 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
> > > > > >
> > > >
> >