Our scalability tests against our web application (350 concurrent users in a
web application using Tomcat 4.1.24 with JDK 1.4.2) is failing due to a
continual leak of database connections. The test failed in that the number
of database connections (reported by the DB server: MS SQL Server) grew to
over a thousand during an hour plus test (using the microsoft sql jdbc
driver though we have tried the i-net driver with similar results). We know
that it is not a problem in the application because we have performed
identical tests except to configure Torque to use the JndiDatasourceFactory.
This in passes the connection pooling chores to the appserver. Both SunOne
appserver and Weblogic appserver maintained a valid number of connections (<
75). We are using Torque 3.1 with DBCP 1.1 (using the
org.apache.commons.dbcp.datasources.SharedPoolDataSource) and Pool 1.1.
Our settings in our torque.properties (which can passed down to the
SHaredPoolDataSource) are:
torque.dsfactory.default.pool.maxActive=100
torque.dsfactory.default.pool.testOnBorrow=0
torque.dsfactory.default.pool.testOnReturn=0
#no setting for maxIdle. It defaults to 8. Not optimal but code should
still work:
torque.dsfactory.default.pool.timeBetweenEvictionRunsMillis=60000
torque.dsfactory.default.pool.numTestsPerEvictionRun=-1
torque.dsfactory.default.pool.minEvictableIdleTimeMillis=1000
torque.dsfactory.default.pool.testWhileIdle=false
I have begun some debugging of this problem. I have added some debug output
in the torqueInstance.getConnection to track size of the pool.
iCountConnections++;
if ((iCountConnections % 100)==0)
{
SharedPoolDataSource spds =
(SharedPoolDataSource)dsf.getDataSource();
log.warn("Current Num Active Connections=" +
String.valueOf(spds.getNumActive()));
log.warn("Current Num Idle Connections=" +
String.valueOf(spds.getNumIdle()));
log.warn("Max Active =" +
String.valueOf(spds.getMaxActive()));
log.warn("Max Idle =" + String.valueOf(spds.getMaxIdle()));
log.warn("Max Wait =" + String.valueOf(spds.getMaxWait()));
}
Here is a sample of the output when I run our scalability tests. At this
point the system is under heavy load and the db server is reporting over 100
connections:
[WARN] TorqueInstance - -Current Num Active Connections=3
[WARN] TorqueInstance - -Current Num Idle Connections=5
[WARN] TorqueInstance - -Max Active =100
[WARN] TorqueInstance - -Max Idle =8
[WARN] TorqueInstance - -Max Wait =500
[WARN] TorqueInstance - -Current Num Active Connections=5
[WARN] TorqueInstance - -Current Num Idle Connections=3
[WARN] TorqueInstance - -Max Active =100
[WARN] TorqueInstance - -Max Idle =8
[WARN] TorqueInstance - -Max Wait =500
[WARN] TorqueInstance - -Current Num Active Connections=19
[WARN] TorqueInstance - -Current Num Idle Connections=0
[WARN] TorqueInstance - -Max Active =100
[WARN] TorqueInstance - -Max Idle =8
[WARN] TorqueInstance - -Max Wait =500
[WARN] TorqueInstance - -Current Num Active Connections=32
[WARN] TorqueInstance - -Current Num Idle Connections=0
[WARN] TorqueInstance - -Max Active =100
[WARN] TorqueInstance - -Max Idle =8
[WARN] TorqueInstance - -Max Wait =500
[WARN] TorqueInstance - -Current Num Active Connections=39
[WARN] TorqueInstance - -Current Num Idle Connections=1
[WARN] TorqueInstance - -Max Active =100
[WARN] TorqueInstance - -Max Idle =8
[WARN] TorqueInstance - -Max Wait =500
[WARN] TorqueInstance - -Current Num Active Connections=40
[WARN] TorqueInstance - -Current Num Idle Connections=0
[WARN] TorqueInstance - -Max Active =100
[WARN] TorqueInstance - -Max Idle =8
[WARN] TorqueInstance - -Max Wait =500
[WARN] TorqueInstance - -Current Num Active Connections=39
[WARN] TorqueInstance - -Current Num Idle Connections=2
[WARN] TorqueInstance - -Max Active =100
[WARN] TorqueInstance - -Max Idle =8
[WARN] TorqueInstance - -Max Wait =500
As you can see, the number of connections reported by the pool is not even
close to the number connections reported by the database.
ToddC
Also we are getting an exception during the test:
java.sql.SQLException: Attempted to use Connection after closed() was
called.
at
org.apache.commons.dbcp.cpdsadapter.ConnectionImpl.assertOpen(ConnectionImpl
.java:140)
at
org.apache.commons.dbcp.cpdsadapter.ConnectionImpl.getMetaData(ConnectionImp
l.java:253)
at org.apache.torque.util.Transaction.rollback(Transaction.java:193)
at
org.apache.torque.util.Transaction.safeRollback(Transaction.java:232)
at com.concur.om.base.BaseCtReportEntry.save(Unknown Source)
After this exception occurs, I receive no more output as shown above. The
system appears deadlocked. I can send a stack dump (Ctrl-Break on Wintel
machines). The stack dump is pretty interesting as it shows where the
contention is within dbcp and pool system but I don't know if it will help
debug this leak problem (e.g. only one thread can create a db connection at
time because the connection to the db is created during makeobject). Let me
know if anyone is interested in seeing the dump.
This problem is critical for us (I had advocated moving to new Torque and
DBCP and now am in a tough spot with this problem). I will continue to
debug what I can and can apply patches fairly easily and run them.
Thanks for any timely help
Todd Carmichael
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