[Pgpool-general] Question about client connections

Wed Dec 19 22:29:37 UTC 2007

Hello,

What is the behavior of pgpool when all of its available connections are
used?  Today I walked through the replication tutorial and was able to
successfully replicate the pgbench data to all of the backends.  Then I
tried running the pgbench benchmark through pgpool and ran into a
problem.  I ran the test several times, each time increasing the number
of clients.  This was working without any problems until the number of
clients exceeded the num_init_children value in the pgpool.conf file.
At this point pgbench seems to hang, and a listing of the pgpool and
postgres processes show them all as IDLE.  The behvior is the same even
if I run pgbench in select-only mode.  I read in another post to the
list that postgres should be configured so that the number of
connections it accepts is larger than (num_init_children * max_pool).
However, even after making this change to each of the backends and
restarting them (as well as pgpool) the pgbench test still hangs.

Is this a bug in some portion of my setup (either pgpool or pgbench), or
is this the expected behavior?  I am new to pgpool so it's quite
possible that something is configured incorrectly. 

The pgbench command I am running is:

pgbench -c 33 -p 9797 bench_replication

Here is the pgpool.conf file I am using:

#
# pgpool-II configuration file sample
# $Header: /cvsroot/pgpool/pgpool-II/pgpool.conf.sample,v 1.15
2007/10/31 10:45:52 y-asaba Exp $

# Host name or IP address to listen on: '*' for all, '' for no TCP/IP
# connections
listen_addresses = 'localhost'

# Port number for pgpool
port = 9797

# Port number for pgpool communication manager
pcp_port = 9898

# Unix domain socket path.  (The Debian package defaults to
# /var/run/postgresql.)
socket_dir = '/tmp'

# Unix domain socket path for pgpool communication manager.
# (Debian package defaults to /var/run/postgresql)
pcp_socket_dir = '/tmp'

# Unix domain socket path for the backend. Debian package defaults to
/var/run/postgresql!
backend_socket_dir = '/tmp'

# pgpool communication manager timeout. 0 means no timeout, but strongly
not rec
ommended!
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 = 300

# If idle for this many seconds, connection to PostgreSQL closes.
# 0 means no timeout.
connection_life_time = 0

# If child_max_connections connections were received, child exits.
# 0 means no exit.
child_max_connections = 0

# If client_idle_limit is n (n > 0), the client is forced to be
# disconnected whenever after n seconds idle (even inside an explicit
# transactions!)
# 0 means no disconnect.
client_idle_limit = 0

# Maximum time in seconds to complete client authentication.
# 0 means no timeout.
authentication_timeout = 60

# Logging directory
logdir = '/tmp'

# Replication mode
replication_mode = true

# 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.
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.
replicate_select = false

# 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.
master_slave_mode = false

# If true, cache connection pool.
connection_cache = true

# Health check timeout.  0 means no timeout.
health_check_timeout = 20

# Health check period.  0 means no health check.
health_check_period = 60

# Health check user
health_check_user = 'postgres'

# Execute command by failover.
# special values:  %d = node id
#                  %h = host name
#                  %p = port number
#                  %D = database cluster path
#                  %% = '%' character
#
failover_command = ''

# Execute command by failback.
# special values:  %d = node id
#                  %h = host name
#                  %p = port number
#                  %D = database cluster path
#                  %% = '%' character
#
failback_command = ''

# 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 = true

# 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.
log_connections = false

# 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 = false

#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 = 'host1'
#backend_port0 = 5432
#backend_weight0 = 1
#backend_data_directory0 = '/data'
#backend_hostname1 = 'host2'
#backend_port1 = 5433
#backend_weight1 = 1
#backend_data_directory1 = '/data1'

backend_hostname0=localhost
backend_port0=5433
backend_weight0=1
backend_data_directory0='/var/lib/pgsql/testdb1'

backend_hostname1=localhost
backend_port1=5434
backend_weight1=1
backend_data_directory1='/var/lib/pgsql/testdb2'

backend_hostname2=localhost
backend_port2=5435
backend_weight2=1
backend_data_directory2='/var/lib/pgsql/testdb3'

backend_hostname3=localhost
backend_port3=5436
backend_weight3=1
backend_data_directory3='/var/lib/pgsql/testdb4'

# - 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

# - online recovery -
# online recovery user
recovery_user = 'nobody'

# online recovery password
recovery_password = ''

# execute a command in first stage.
recovery_1st_stage_command = ''

# execute a command in second stage.
recovery_2nd_stage_command = ''

Thanks!