Contention for DriverManager when initializing multiple datasources
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Key: DBCP-272
URL: https://issues.apache.org/jira/browse/DBCP-272
Project: Commons Dbcp
Issue Type: Bug
Affects Versions: 1.2.2
Environment: Java HotSpot(TM) 64-Bit Server VM (1.6.0-b105 mixed mode)
on Linux
Reporter: Adrian Woodhead
This issue has been discussed in the commons user's mailing list between
myself, Simon Kitching and Phil Steitz.
In summary:
I have a webapp deployed in tomcat containing 3 pooled datasources which are
managed by Spring. The webapp starts up OK and is immediately hit by a load of
a few hundred requests a second. It seems to handle a few hundred request and
then just locks up entirely and stops responding entirely. Attached is a stack
trace obtained by doing kill -3 when in this state. After discussion on the
mailing list I changed the datasources to be non-lazy initialised in spring but
the issue still occurs.
Simon Kitching said:
"The first thread is trying to initialise a postgresql driver and register it
with DriverManager. The driver registration is being triggered from a static
initialiser block on the postgresql driver class, so is executing from within
the Class.forName method (and therefore the postgresql driver Class object is
locked by this thread).
The second thread is trying to initialise a mysql driver and register it with
DriverManager. Again, the driver registration is being triggered from a static
initialiser block on the mysql driver class, so the mysql driver Class object
is locked by this thread).
But in both cases, the DriverManager needs to be initialised before anything
can be registered. The first thread appears to have run first, triggering the
initialisation process, and the second thread is blocked waiting for
initialisation of DriverManager to complete before it registers the mysql
driver.
<snip/>
Possibly dbcp should call DriverManager.getDrivers() internally on startup to
avoid this race... "
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