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From jburwell <...@git.apache.org>
Subject [GitHub] cloudstack issue #1762: CLOUDSTACK-9595 Transactions are not getting retried...
Date Mon, 14 Nov 2016 16:11:50 GMT
Github user jburwell commented on the issue:

    https://github.com/apache/cloudstack/pull/1762
  
    @yvsubhash according to the (MySQL deadlock documenation)[http://dev.mysql.com/doc/refman/5.7/en/innodb-deadlocks.html],
 a `MYSQL_DEADLOCK_ERROR_CODE` error indicates the enclosing transaction has been rolled back.
 The proper handling for this error is to re-execute all statements executed in the aborted
transaction.  From a best practices perspective, all base data should be re-retrieved and
changed to ensure logical consistency with changes made by the transaction that won deadlock
resolution.
    
    As I understand this patch, only the most recently executed DML is retried.  Therefore,
any previously executed changes will be discarded and the DML will be re-executed either in
a new transaction or in auto-commit (I didn't look up how the client handles the transaction
context in this scenario).  If my understanding is correct, this patch could lead to issues
ranging from unexpected foreign key integrity errors to data corruption.
    
    Rather attempting to implement a generic retry, I think the best approach to addressing
deadlocks is to treat them bugs.  This patch could be modified to provide detailed logging
information about the conditions under which a deadlock occurs providing the information necessary
to refactor the system to avoid lock contention.


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