Question

I recently switched to Spring Framework instead of manually handling JDBC, and it is mostly a good transition. One program started having strange problems, though: if the database is slow, when calling getJdbcTemplate().update( ... ) it sometimes never returns.

After researching a little bit, I switched from Apache DBCP to C3PO, but the problem still came back.

Here’s the code I’m using:

public class MyDao extends SimpleJdbcDaoSupport {
    private static Logger logger = Logger.getLogger(MyDao.class);

    public MyDao(Config config) {
        super();

        ComboPooledDataSource cpds = new ComboPooledDataSource();
        try {
            cpds.setDriverClass("com.mysql.jdbc.Driver");
        } catch (PropertyVetoException e) {
            throw new RuntimeException(e);
        }
        cpds.setUser("username");
        cpds.setPassword("password");
        cpds.setJdbcUrl("jdbc:mysql://localhost/schema" + 
                        "?useUnicode=true&characterEncoding=UTF-8");
        cpds.setMaxStatements( 180 );
        cpds.setPreferredTestQuery("SELECT 1");
        cpds.setTestConnectionOnCheckout(true);

        this.setDataSource(cpds);
    }

    public void addToWorkQueue(String item) {
        long[] ids = Utils.getItemIds(item);

        try {
            logger.debug("About to insert to work table");
            getJdbcTemplate().update(
                    "INSERT IGNORE INTO work " +
                    "SELECT * FROM queue WHERE id_1 = ? AND id_2 = ?",
                    new Object[] { ids[0], ids[1] }
            );
        } finally {
            logger.debug("Updated work table");
        }
    }
}

Here’s what it looks like in the log file:

2009-07-29 17:37:13.570 com.mycomp.MyDao About to insert into work table
2009-07-29 17:37:13.570 com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool Testing PooledConnection [com.mchange.v2.c3p0.impl.NewPooledConnection@170984c] on CHECKOUT.
2009-07-29 17:37:13.571 com.mchange.v2.c3p0.stmt.GooGooStatementCache checkinAll(): com.mchange.v2.c3p0.stmt.GlobalMaxOnlyStatementCache stats -- total size: 1; checked out: 0; num connections: 1; num keys: 1
2009-07-29 17:37:13.571 com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool Test of PooledConnection [com.mchange.v2.c3p0.impl.NewPooledConnection@170984c] on CHECKOUT has SUCCEEDED.
2009-07-29 17:37:13.571 com.mchange.v2.resourcepool.BasicResourcePool trace com.mchange.v2.resourcepool.BasicResourcePool@d402dd [managed: 3, unused: 2, excluded: 0] (e.g. com.mchange.v2.c3p0.impl.NewPooledConnection@170984c)
2009-07-29 17:37:13.571 com.mchange.v2.c3p0.stmt.GooGooStatementCache com.mchange.v2.c3p0.stmt.GlobalMaxOnlyStatementCache ----> CACHE HIT
2009-07-29 17:37:13.571 com.mchange.v2.c3p0.stmt.GooGooStatementCache checkoutStatement: com.mchange.v2.c3p0.stmt.GlobalMaxOnlyStatementCache stats -- total size: 1; checked out: 1; num connections: 1; num keys: 1

This is where the code hangs. Usually it just goes on like this:

2009-07-29 17:37:13.762 com.mchange.v2.c3p0.stmt.GooGooStatementCache checkinStatement(): com.mchange.v2.c3p0.stmt.GlobalMaxOnlyStatementCache stats -- total size: 1; checked out: 0; num connections: 1; num keys: 1
2009-07-29 17:37:13.763 com.mchange.v2.c3p0.stmt.GooGooStatementCache checkinAll(): com.mchange.v2.c3p0.stmt.GlobalMaxOnlyStatementCache stats -- total size: 1; checked out: 0; num connections: 1; num keys: 1
2009-07-29 17:37:13.763 com.mchange.v2.resourcepool.BasicResourcePool trace com.mchange.v2.resourcepool.BasicResourcePool@d402dd [managed: 3, unused: 2, excluded: 0] (e.g. com.mchange.v2.c3p0.impl.NewPooledConnection@170984c)
2009-07-29 17:37:13.763 com.mycomp.MyDao Updated work table

I don’t know why I’m not getting any log message from Spring Framework itself. I added these lines in my main code:

Logger springLogger = Logger.getLogger("org.springframework");
springLogger.setLevel(Level.TRACE);
springLogger.debug("testing spring logger");

The test message shows, but nothing else. Sorry for diverging.

I did notice a slowdown before the hang. The last time the query ran successfully it took a minute and a half to finish, instead of the usual 200ms. The next time, I let it run for 25 minutes before killing the process.

I know I have some problems with my database (InnoDB), which I’m working on, but this seems like after a timeout, Spring Framework just “gives up” and hangs.

Any advice would be appreciated.

Answer 1

Eventually, the problem was avoided by fixing the underlying DB issue.

I was using an InnoDB table as a work queue, which meant I added and removed a whole lot of items to it. The table never had too many rows at a given time, but apparently InnoDB can’t handle this sort of work, or as my DBA friend put it, “deleting rows from a table doesn’t do anything for performance”.

After switching to a much crazier db strategy, which involved creating and dropping tables all the time, the performance was much improved and the hangs went away.

So I guess what I’m saying is, skaffman’s comment was probably right. This didn’t have anything to do with Spring.