[pgpool-general: 8181] Re: Unable to acquire JDBC Connection

[Bo Peng]

Hello,

> Hello!
> 
> Thank you for response.
> 
> We run 3 replicas of Pgpool in k8s.
> 
> NUM_INIT_CHILDREN=400, MAX_POOL=2, LISTEN_BACKLOG_MULTIPLIER=2
> 
> On PostgreSQL max_connections=2500 . We set very big value here now to 
> test only pgpool for a lack of connection.
> 
> When load is running max number of connections to PostgreSQL is slightly 
> over 200 (i.e. 212, 220). At that time command "SHOW POOL_PROCESSES" on 
> Pgpool shows many idle processes.
> 
> And if I understand correctly, if cause of the error "Unable to acquire 
> JDBC Connection" was in lack of connections, Pgpool would issue an error 
> message about that.

By default, Pgpool-II doesn't return an error message.
By default, Pgpool-II accepts up to num_init_children connection requests and
queues up more connection requests until one of child process becomes free. 

If you set reserved_connections parameter, Pgpool-II will return an error message
"Sorry, too many clients already" if the limit is reached.

For example:
reserved_connections = 1

https://www.pgpool.net/docs/latest/en/html/runtime-config-connection.html#GUC-RESERVED-CONNECTIONS

> On 25.05.2022 09:15, Bo Peng wrote:
> > Hello,
> >
> >> Hello,
> >>
> >> Our application use Pgpool in k8s with docker image pgpool/pgpool2, and
> >> our PostgreSQL nodes are on virtual machines.
> >>
> >> When we tried to perform load test our application, we have received a
> >> lot of errors of application services that connect to database through
> >> Pgpool:
> >>
> >> "Could not open JPA EntityManager for transaction; nested exception is
> >> org.hibernate.exception.JDBCConnectionException: Unable to acquire JDBC
> >> Connection"
> >>
> >> If application connects to database directly  without Pgpool, this error
> >> does not appear.
> > The setting of num_init_children may cause this error.
> > Could you run ps command and check if there are processes in the "wait for connection request" status?
> >
> > How many Pgopol-II replicas do you configured?
> > What are the values of num_init_children, max_pool and PostgreSQL's max_connections.
> >
> >> Do you have any experience with such problem and could you tell why it
> >> occurs, i.e. why the service can't connect Pgpool and how to fix it?
> >>
> >> Thanks in advance.
> >>
> >> -- 
> >> Regards,
> >>     Nikola
> >>
> >> _______________________________________________
> >> pgpool-general mailing list
> >> pgpool-general at pgpool.net
> >> http://www.pgpool.net/mailman/listinfo/pgpool-general
> >


-- 
Bo Peng <pengbo at sraoss.co.jp>
SRA OSS, Inc. Japan
http://www.sraoss.co.jp/