Eugene Koifman created HIVE-16321:
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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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