On a development system that I have been working on lately, the MySql database connections have been dropping out due to a lack of activity overnight (> 8 hours - a default timeout).
There doesn't seem to be a suitable corresponding timeout setting for the default connection pooling system for the corresponding Grails datasource (DBCP), so I've gone looking at what the alternative pooling systems have to offer, and how they could be configured to replace the default Grails DataSource.
On the surface of things development for dbcp and c3p0 seem quite inactive. Although dbcp shows a bunch of updates coming in their next release, it has now been over a year since their last release.
The Hibernate guys appear to have stopped supporting use for Hibernate with DBCP
C3P0 seems to use SourceForge to allow downloads, but keeps the documentation elsewhere.
Proxool looks like it could have potential - pity the user mailing lists are full of spam, so the likelihood of getting community involvement is remote.
C3P0 will do for today.
Update: I just attended a SpringSource talk on tcServer in London, during which Mark Thomas mentioned that the Tomcat developers have been working on their own connection pooling implementation, and that he is in the process of contributing some fixes to DBCP. (No mention of c3p0).