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From "John H. Embretsen (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-2877) Print the entire lock list when a deadlock occurs and deadlock tracing is on
Date Wed, 27 Jun 2007 14:05:25 GMT
Print the entire lock list when a deadlock occurs and deadlock tracing is on

                 Key: DERBY-2877
                 URL: https://issues.apache.org/jira/browse/DERBY-2877
             Project: Derby
          Issue Type: Improvement
          Components: Services
    Affects Versions:
            Reporter: John H. Embretsen

When a deadlock occurs, derby includes the cycle of locks which caused the deadlock in the
SQLException message. This is also printed to derby.log if the properties derby.locks.deadlockTrace
and derby.locks.monitor are set to true, or if debug code is being used (e.g. jars from lib-debug
distributions). It will be easier to debug deadlocks if the entire lock table is printed to
derby.log as well (alternatively to both derby.log and the exception message) in these cases.
An example of such a lock table is available at http://wiki.apache.org/db-derby/LockDebugging.

For example, in a long-running test I have observed deadlocks with lock cycle messages such

Lock : ROW, DELETED, (2,1)
  Waiting XID : {6241401573, S} , U1, DELETE FROM "U1"."DELETED" WHERE CURRENT OF "SQL_CURLH000C9"
  Granted XID : {6241401662, S} 
Lock : ROW, DELETED, (3,3523)
  Waiting XID : {6241401662, U} , U1, SELECT ITEMID FROM DELETED
  Granted XID : {6241401573, U} 
. The selected victim is XID : 6241401573.

It is not clear from this output why XID 6241401573 is waiting for a shared lock (S) on row
(2,1), as an S lock is compatible with other S locks [1]. 

Having a snapshot of the contents of the lock table at the time of the deadlock would probably
help a great deal in the debugging process. 

[1]: Lock compatibility: http://db.apache.org/derby/docs/dev/devguide/rdevconcepts2462.html

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