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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2877) Print the entire lock list when a deadlock occurs and deadlock tracing is on
Date Wed, 27 Jun 2007 14:32:25 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12508563
] 

Daniel John Debrunner commented on DERBY-2877:
----------------------------------------------

The entire contents of the lock table could also hinder debugging by providing too much information,
making it hard to find the actual problem. Imagine an active system with 100 users and two
of them deadlock, now one would have to sift through 98 unrelated transactions.

Maybe the approach could be to figure out what would make the deadlock message more useful
while displaying only  the relevant information.
E.g. in the example deadlock you have above, possibly there is a bug in what information is
being displayed, maybe fixing the bug would be a better approach than drowning the log with
too much information?

> 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: 10.2.2.0
>            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 as:
> 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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