Mysterious (dead?)locking

Hi.

When we use HSQLDB for some system tests of a deployed webapp, about 60% of
the time the system freezes without completing.

We're on 2.3.0, and have moved to using MVCC.

On examination of the locked sessions, it would seem that everything is
waiting on a 'Checkpoint' operation (see below) by looking
at INFORMATION_SCHEMA.SYSTEM_SESSIONS - Everything is waiting on this, but
this is allegedly not waiting on anything itself.

The thread dump shows the checkpoint is coming from a regular timed task.

Is there anything I can do to further diagnose this, as I can't understand
why it's reporting connection 10 isn't waiting on anything - but the system
is locked solid.




INFORMATION_SCHEMA.SYSTEM_SESSIONS:
-----------------------------------------------------
[3, 2013-12-24 10:39:06.0, SA, true, true, false, 0, PUBLIC, false, 0, ,
10, SELECT VERSION FROM KMS_VERSION WHERE ID='KMS', 1]
[6, 2013-12-24 10:39:17.0, SA, true, false, false, 0, PUBLIC, false, 0, ,
10, SELECT * FROM QRTZ_SCHEDULER_STATE WHERE SCHED_NAME =
'schedulerFactoryBean', 1]
[7, 2013-12-24 10:39:34.0, SA, true, false, false, 0, PUBLIC, false, 0, ,
10, SELECT TRIGGER_NAME, TRIGGER_GROUP, NEXT_FIRE_TIME, PRIORITY FROM
QRTZ_TRIGGERS WHERE SCHED_NAME = 'schedulerFactoryBean' AND TRIGGER_STATE =
? AND NEXT_FIRE_TIME <= ? AND (MISFIRE_INSTR = -1 OR (MISFIRE_INSTR != -1
AND NEXT_FIRE_TIME >= ?)) ORDER BY NEXT_FIRE_TIME ASC, PRIORITY DESC, 1]
*[10, 2013-12-24 10:41:53.0, _SYSTEM, true, false, false, 0, PUBLIC, false,
0, 3,7,6,11, , CHECKPOINT, 1]*
[11, 2013-12-24 10:42:13.0, SA, true, false, false, 0, PUBLIC, false, 0, ,
10, SELECT COUNT(TRIGGER_NAME) FROM QRTZ_TRIGGERS WHERE SCHED_NAME =
'schedulerFactoryBean' AND NOT (MISFIRE_INSTR = -1) AND NEXT_FIRE_TIME < ?
AND TRIGGER_STATE = ?, 1]
[13, 2013-12-24 11:26:17.0, SA, true, false, false, 0, PUBLIC, false, 0, ,
, select * FROM INFORMATION_SCHEMA.SYSTEM_SESSIONS, 0]

Thread dump
----------------
Thread t@31: (state = BLOCKED)
 - sun.misc.Unsafe.park(boolean, long) @bci=0 (Compiled frame; information
may be imprecise)
 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=14,
line=158 (Interpreted frame)
 -
java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt()
@bci=1, line=811 (Interpreted frame)
 -
java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(int)
@bci=55, line=969 (Interpreted frame)
 -
java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(int)
@bci=24, line=1281 (Interpreted frame)
 - java.util.concurrent.CountDownLatch.await() @bci=5, line=207
(Interpreted frame)
 - org.hsqldb.lib.CountUpDownLatch.await() @bci=12 (Compiled frame)
 - org.hsqldb.Session.executeCompiledStatement(org.hsqldb.Statement,
java.lang.Object[], int) @bci=289 (Compiled frame)
 - org.hsqldb.Database$CheckpointRunner.run() @bci=25 (Interpreted frame)
 - org.hsqldb.lib.HsqlTimer$TaskRunner.run() @bci=19 (Interpreted frame)
 - java.lang.Thread.run() @bci=11, line=662 (Interpreted frame)

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