[pgpool-general: 3867] Re: pgpool configuration

[Yugo Nagata]

Hi,

pgpool-II generates 200 processes and connections to PostgreSQL,
and 200 clients can connect to pgpool-II simultaneously, since num_init_children=200. Other clients are to wait for connection
in the listen queue of OS.

The length of listen queue can be controlled by listen_backlog_multiplier
parameter. The default is 2, so the queue length is 400 (= 200 * 2).
(In acutual, the length is decided by OS kernel.)
If the queue is overflowing, OS retries connection several times
(tcp_syn_retries) before it fails. This causes performance degression
or connection error. So, specifying listen_backlog_multiplier to
larger value might be resolve your situation.

You can check if the overflow occurs by `netstat -s`. If so,
a message like the following is in TcpExt part.

 535 times the listen queue of a socket overflowed


I don't know why only 60 connection are used with Tomcat JDBC
connection pool. However, I think this can be affected by Tomcat configuration like maxThreads, maxActive and so on.


On Tue, 7 Jul 2015 12:48:03 +0000 (UTC)
Ioana Danes <ioanasoftware at yahoo.ca> wrote:

> Hi Everyone,
> 
> I am doing a performance test on pgpool only for pooling, no replication, no failover and no load balancing. 
> 
> Here is a snapshot of the pgpool parameters I thought are relevant:
> 
> num_init_children = 200
> max_pool = 1
> child_life_time = 300
> child_max_connections = 0
> connection_life_time = 0
> client_idle_limit = 0
> 
> connection_cache = on
> reset_query_list = 'ABORT; DISCARD ALL'
> 
> replication_mode = off
> load_balance_mode = off
> master_slave_mode = off
> use_watchdog = off
> 
> 
> Postgres database has max_connections = 250 and there is no other application using it.
> 
> 
> I am using 1300 clients and with tomcat jdbc connection pool it typically needs around 60 database connections. When I am using pgpool instead of tomcat jdbc connection pool I run out of the 200 connections when not even half of the clients are running.
> 
> Error from the web application:
> 
> persistence.StorageException: The connection attempt failed.
> 
> pgpool-II-3.4.2-1.3
> postgresql94-9.4.1-7.2
> 
> SUSE Linux Enterprise Server 11 (x86_64)
> VERSION = 11
> PATCHLEVEL = 3
> 
> 
> 
> Is this the expected behaviour, is Tomcat connection pooling better that pgpool at reusing connections or I am doing something wrong?
> 
> Thank you,
> ioana
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-- 
Yugo Nagata <nagata at sraoss.co.jp>