We are using DBCP with iBatis in a JSF/Ajax webapp running in Tomcat with an
Oracle database.
The application has quite high load and concrrency, and the database is very
loaded. The application is running fine for some days but then freezes at peak
hours.
When I look at a thread dump made while the app hangs, I can see as many
threads as we have connections in the pool (64) in BLOCKED state while calling
either borrowObject() or returnObject(), please see the two examples below. It
looks like some kind of deadlock and the only way out of it seems to be a
restart of Tomcat.
First I thought this is normal with the WHEN_EXHAUSTED_LOCK action, but since
we have maxWait set to 1000 I'd not expect this kind of blocking to happen.
I tried to reproduce the behavior with a small test app, but here the threads
go in TIMED_WAIT state when the pool is exhausted and become RUNNABLE again as
soon as some connection became available again.
I really don't understand what is happening and why the pool gets locked up
that way.
Any hint/suggestion welcome!
Torsten
"TP-Processor483" daemon prio=10 tid=0x01fe5000 nid=0x11f7 waiting for monitor
entry [0x8d87e000..0x8d881788]
java.lang.Thread.State: BLOCKED (on object monitor)
at
org.apache.commons.pool.impl.GenericObjectPool.returnObject(GenericObjectPool.java:916)
- waiting to lock <0x9ddf7460> (a
org.apache.commons.pool.impl.GenericObjectPool)
at
org.apache.commons.dbcp.PoolableConnection.close(PoolableConnection.java:87)
- locked <0xf83f9eb8> (a org.apache.commons.dbcp.PoolableConnection)
at
org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.close(PoolingDataSource.java:181)
at
com.ibatis.sqlmap.engine.transaction.jdbc.JdbcTransaction.close(JdbcTransaction.java:81)
at
com.ibatis.sqlmap.engine.transaction.TransactionManager.end(TransactionManager.java:110)
"TP-Processor382" daemon prio=10 tid=0x026f6000 nid=0x25a waiting for monitor
entry [0x7de7f000..0x7de81808]
java.lang.Thread.State: BLOCKED (on object monitor)
at
org.apache.commons.pool.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:781)
- waiting to lock <0x9ddf7460> (a
org.apache.commons.pool.impl.GenericObjectPool)
at
org.apache.commons.dbcp.PoolingDataSource.getConnection(PoolingDataSource.java:96)
at
org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:880)
at
com.ibatis.sqlmap.engine.transaction.jdbc.JdbcTransaction.init(JdbcTransaction.java:48)
at
com.ibatis.sqlmap.engine.transaction.jdbc.JdbcTransaction.getConnection(JdbcTransaction.java:89)
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