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https://issues.apache.org/jira/browse/HIVE-15077?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eugene Koifman updated HIVE-15077:
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Priority: Blocker (was: Major)
> 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
> Priority: Blocker
>
> 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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