Reconnecting to a postgres database after postgres restart from Java

Question

I'm using postgres 9.1, org.apache.commons.dbcp.BasicDataSource (for my connection pool) and Java 1.7. When I restart my postgres server, I get exceptions like org.postgresql.util.PSQLException: FATAL: terminating connection due to administrator command .

How can I make it so the connections automatically re-connect to the restarted database?

Answer 1

DBCP has a connection validation query option - validationQuery , according to the docs . You can set it to something like SELECT 1; and DBCP will run that before returning a connection to test it.

That said, your app really should handle this case. SQL queries can fail for all sorts of reasons and you should always do your queries in a retry loop with a time back-off and retry limit, plus some logic to decide what exceptions are recoverable on retry and which aren't (use the SQLState for that).

In particular, validation is subject to a race condition where you can have event orderings like:

1. Validate
2. Pass connection to app
3. Server shutdown
4. App runs first statement

or

1. Validate
2. Pass connection to app
3. App runs first statement, opening a transaction
4. Server shutdown
5. App runs second statement

... so it remains important for your app to have a proper retry loop and good transaction handling.

You can get the SQLState from the SQLException: SQLException.getSQLState . The codes for PostgreSQL are in the PostgreSQL manual .

Answer 2

In this particular case the PostgreSQL connection is telling you that the server was shut down after the connection was created. DBCP connection pool does not handle this condition with it's default configuration.

Even if you set validationQuery parameter to something like SELECT 1 , it will not be used, unless you also set at least one of the testOnXXXX parameters.

I usually set both testOnCreate and testOnBorrow to true .

Also check other defaults of DBCP (in the org.apache.commons.pool2.impl.BaseObjectPoolConfig), because in my opinion they are not well suited for production environments.