Caused by: org.postgresql.util.PSQLException: FATAL: remaining connection slots are reserved for non-replication superuser connections

Question

I use c3p0-0.9.5.2.jar and mchange-commons-java-0.2.11.jar to manage the pool connection, And I use postgreSql 9.3.

I get these messages at least once a day in my Prod environment :

Caused by: java.sql.SQLException: Connections could not be acquired from the underlying database!
    at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:118)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:692)
    at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:140)
    at org.springframework.orm.hibernate3.LocalDataSourceConnectionProvider.getConnection(LocalDataSourceConnectionProvider.java:81)
    at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
    ... 212 more
Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.
    at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1469)
    at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:644)
    at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:554)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutAndMarkConnectionInUse(C3P0PooledConnectionPool.java:758)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:685)
    ... 215 more
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:712)

I have this config in my aplication :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
"http://www.springframework.org/dtd/spring-beans.dtd">

<beans>
         <bean id="dataSource" class = "com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
       <property name="driverClass" value="org.postgresql.Driver"/>

        <property name="jdbcUrl" value="jdbc:postgresql://localhost:5432/Test"/> 

        <property name="user" value="postgres"/>
        <property name="password" value="postgres"/>
           <!-- pool sizing -->
     <!-- pool sizing -->
        <property name="initialPoolSize" value="32" />
        <property name="minPoolSize" value="30" />
        <property name="maxPoolSize" value="300" />
        <property name="acquireIncrement" value="10" />
        <property name="maxStatements" value="0" />

        <!-- retries -->
        <property name="acquireRetryAttempts" value="30" />
        <property name="acquireRetryDelay" value="1000" /> <!-- 1s -->
        <property name="breakAfterAcquireFailure" value="false" />

        <!-- refreshing connections -->
        <property name="maxIdleTime" value="180" /> <!-- 3min -->
        <property name="maxConnectionAge" value="10" /> <!-- 1h -->

        <!-- timeouts and testing -->
        <property name="checkoutTimeout" value="0" /> <!-- 60s -->
        <property name="idleConnectionTestPeriod" value="60" /> <!-- 60 -->
        <property name="testConnectionOnCheckout" value="true" />
        <property name="preferredTestQuery" value="SELECT 1" />
        <property name="testConnectionOnCheckin" value="true" /> 

    </bean>
</beans>

in postgresql.conf I have this config :

max_connections = 300
shared_buffers = 32GB

my server has this performance: 24 cpu, 256 GB memory

the number of users using the application is around 1300

is there anyone who can help me to solve this problem

thank you in advance

Answer 1

There are superuser_reserved_connections connections slots (3 by default) that are reserved for superusers so that they can connect even in a situation where all connection slots are taken.

So you effectively only have 297 slots available.

Either reduce the maximum number of connections of your connection pool or increase max_connections in PostgreSQL.

By the way, 300 is much too high. You should use a much lower setting with a connection pool (unless you have hundreds of cores in your database machine).