Derby
  1. Derby
  2. DERBY-2877

Print the entire lock list when a deadlock occurs and deadlock tracing is on

    Details

    • Type: Improvement Improvement
    • Status: Closed
    • Priority: Major Major
    • Resolution: Cannot Reproduce
    • Affects Version/s: 10.2.2.0
    • Fix Version/s: None
    • Component/s: Services
    • Labels:
      None

      Description

      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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            • Assignee:
              Unassigned
              Reporter:
              John H. Embretsen
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              • Created:
                Updated:
                Resolved:

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