[jira] [Created] (HIVE-16321) Possible deadlock in metastore with Acid workload

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

Eugene Koifman created HIVE-16321:
-------------------------------------

             Summary: Possible deadlock in metastore with Acid workload
                 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


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 X simultaneous calls to  TxnHandlerlock(), 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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