Eugene Koifman created HIVE-15077:
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Summary: Acid LockManager is unfair
Key: HIVE-15077
URL: https://issues.apache.org/jira/browse/HIVE-15077
Project: Hive
Issue Type: Bug
Components: Transactions
Reporter: Eugene Koifman
Assignee: Eugene Koifman
HIVE-10242 made the acid LM unfair.
In TxnHandler.checkLock(), suppose we are trying to acquire SR5 (the number is
extLockId).
Then
LockInfo[] locks = lockSet.toArray(new LockInfo[lockSet.size()]);
may look like this (all explicitly listed locks are in Waiting state)
{...., SR5 SW3 X4}
So the algorithm will find SR5 in the list and start looking backwards.
According to IDs, SR5 should wait for X4 to be granted but X4 won't even be
examined and so SR5 may be granted.
Theoretically, this could cause starvation.
The query that generates the list already has
query.append(" and hl_lock_ext_id <= ").append(extLockId);
but it should use "<" rather than "<=" to exclude the locks being checked from
"locks" list which will make the algorithm look at all locks "in front" of a
given lock.
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