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From wangzw <...@git.apache.org>
Subject [GitHub] incubator-hawq pull request: HAWQ-255: change CHECKPOINT_START_LOC...
Date Thu, 17 Dec 2015 07:52:58 GMT
Github user wangzw commented on a diff in the pull request:

    --- Diff: src/backend/storage/smgr/smgr.c ---
    @@ -1327,28 +1327,6 @@ smgrDoDeleteActions(
     						palloc0((*listCount) * sizeof(PersistentFileSysObjStateChangeResult));
    -	 * There are two situations where we get here. CommitTransaction()/AbortTransaction()
or via
    -	 * AbortSubTransaction(). In the first case, we have already obtained the MirroredLock
    -	 * CheckPointStartLock. In the second case, we have not obtained the locks, so we attempt
    -	 * to get them to make sure proper lock order is maintained.
    -	 *
    -	 * Normally, if a relation lock is needed, it is obtained before the MirroredLock and
    -	 * but we have not yet obtained an EXCLUSIVE LockRelationForResynchronize. This lock
will be obtained in
    -	 * PersistentFileSysObj_EndXactDrop(). This is an exception to the normal lock ordering,
which is done
    -	 * to reduce the time that the lock is held, thus allowing a larger window of time for
    -	 * resynchronization to obtain the lock.
    -	 */
    -	/*
    -	 * The logic will eventually obtain a CheckpointStartLock in PersistentRelation_Dropped(),
    -	 * but functions called from this function my obtain Exclusive locks before the
    -	 * CheckpointStartLock is obtained. This could cause a potential deadlock in the future.
    -	 * We need to take a CheckpointStartLock here to maintain proper lock ordering
    -	 * (i.e. MirrorLock -> CheckpointStartLock ).
    -	 */
    --- End diff --
    Although we do not have a mirror any more, but we still have MirrorLock (should be removed).
If we remove this lock, can we still keep the lock ordering and prevent from dead locking?

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