Solving the famous "java.sql.SQLException: Total number of available connections are less than the total number of closed connections" issue

While starting up your WSO2 product after configuring a registry mount, you may have come across the below issue.

Caused by: java.sql.SQLException: Total number of available connections are less than the total number of closed connections
    at org.wso2.carbon.registry.core.jdbc.dataaccess.JDBCDatabaseTransaction$ManagedRegistryConnection.close(JDBCDatabaseTransaction.java:1349)
    at org.wso2.carbon.registry.core.jdbc.dataaccess.JDBCTransactionManager.endTransaction(JDBCTransactionManager.java:178)
    ... 46 more


When you see the above exception, the first thing you have to do is verify the mount configuration of the registry.xml.

See below. In this config, if you accidentally refer to the dbConfig name of the local DB in the mount, you will get the exception mentioned in the $subject.The correct dbConfig name you should refer to is, wso2Mount where wso2Mount is pointed to an external DB.

E.g. :-

     <currentDBConfig>wso2registry</currentDBConfig>
    <readOnly>false</readOnly>
    <enableCache>true</enableCache>
    <registryRoot>/</registryRoot>

    <dbConfig name="wso2registry">
        <dataSource>jdbc/WSO2CarbonDB</dataSource>
    </dbConfig>

    <dbConfig name="wso2Mount">
        <dataSource>jdbc/WSO2RegDB</dataSource>
    </dbConfig>

    <remoteInstance url="https://localhost:9443/registry">
        <id>instanceid</id>
        <dbConfig>wso2Mount</dbConfig>
        <readOnly>false</readOnly>
        <enableCache>true</enableCache>
        <registryRoot>/</registryRoot>
    </remoteInstance>

    <mount path="/_system/config" overwrite="true">
        <instanceId>instanceid</instanceId>
        <targetPath>/_system/nodes</targetPath>
    </mount>