[jira] [Issue Comment Deleted] (HIVE-16321) Possible deadlock in metastore with Acid enabled

["Eugene Koifman (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-16321?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Eugene Koifman updated HIVE-16321:
----------------------------------
    Comment: was deleted

(was: don't get why this failed to apply....)

> Possible deadlock in metastore with Acid enabled
> ------------------------------------------------
>
>                 Key: HIVE-16321
>                 URL: https://issues.apache.org/jira/browse/HIVE-16321
>             Project: Hive
>          Issue Type: Bug
>          Components: Transactions
>    Affects Versions: 1.3.0
>            Reporter: Eugene Koifman
>            Assignee: Eugene Koifman
>            Priority: Blocker
>         Attachments: HIVE-16321.01.branch-2.patch, HIVE-16321.01.patch, HIVE-16321.02.branch-2.patch, HIVE-16321.02.patch, HIVE-16321.03-branch-2.patch, HIVE-16321.03.patch
>
>
> TxnStore.MutexAPI is a mechanism how different Metastore instances can coordinate their operations.  It uses a JDBCConnection to achieve it.
> In some cases this may lead to deadlock.  TxnHandler uses a connection pool of fixed size.  Suppose you have X simultaneous calls to  TxnHandler.lock(), where X is >= size of the pool.  This take all connections form the pool, so when
> {noformat}
> handle = getMutexAPI().acquireLock(MUTEX_KEY.CheckLock.name());
> {noformat} 
> is executed in _TxnHandler.checkLock(Connection dbConn, long extLockId)_ the pool is empty and the system is deadlocked.
> MutexAPI can't use the same connection as the operation it's protecting.  (TxnHandler.checkLock(Connection dbConn, long extLockId) is an example).
> We could make MutexAPI use a separate connection pool (size > 'primary' conn pool).
> Or we could make TxnHandler.lock(LockRequest rqst) return immediately after enqueueing the lock with the expectation that the caller will always follow up with a call to checkLock(CheckLockRequest rqst).
> cc [~f1sherox]



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