如何找到哪个应用程序保留了Postgres连接？

Question

There are several applications running on Tomcat. They use Postgres databases and sometimes exceed the max connection limit:

org.hibernate.exception.GenericJDBCException: Error calling Driver#connect         at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:47)

Caused by: org.postgresql.util.PSQLException: FATAL: remaining connection slots are reserved for non-replication superuser connections
    at org.postgresql.core.v3.ConnectionFactoryImpl.readStartupMessages(ConnectionFactoryImpl.java:684)

I have tried to increase the limit ( How to resolve FATAL: connection limit exceeded for non-superusers ) but the problem remains. How to find out which application takes over connection slots?

Answer 1

Add ApplicationName to the connection string, like here:

jdbc:postgresql://localhost:5435/MyDB?ApplicationName=MyApp

then you will see it in:

select application_name, count(1), state 
from pg_stat_activity 
group by application_name, state;

This will work only if you have separate connection strings for different applications of course.

Also check some info on connections pooling with JDBC.