DBCP returns closed connections

Question

We are seeing situations where our database connection from org.apache.commons.dbcp.BasicDataSource is dying with socket write errors:

com.micro         


        

Answer 1

The pooled connection has been closed by the DB. That can mean 2 things:

1. The connection pool holds connections open for too long.
2. The DB closes connections after a too short time.

In theory, increasing/decreasing the timeout on either sides to align it should fix the problem.

On DBCP, your best bet is to validate connections before returning by a testOnBorrow=true and a validationQuery setting, e.g. SELECT 1. You can find configuration options in the Tomcat JDBC data sources documentation.

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Update as per your update:

Here's a more succint version of what I'd like to know:

Connection c1, c2;
c1 = DatabaseManager.getConnection();
// c1.close() not called
c2 = DatabaseManager.getConnection(); 

Is "c1 == c2" a true statement? Or have two connections been allocated?

It are two distinct connections. Only if you call c1.close() then there's a reasonable chance that c2 returns the same connection.

And if it's the latter, would code like this represent a "connection pool leak":

Connection c1;
c1 = DatabaseManager.getConnection();
// c1.close() not called
c1 = DatabaseManager.getConnection();

Yes, definitely it will leak the first connection as it's never been returned to the pool. You should always close all DB resources in the shortest possible scope in a try-finally block. A bit decent connection pool is however configureable to reap abandoned connections, but this should definitely not be used as "workaround".

Answer 2

I was also facing the same issues. then i realized that i was making multiple asynchronous ajax calls that was causing the issue.

I serialized the calls and it fixed the issue.