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https://issues.apache.org/jira/browse/HIVE-21354?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17082966#comment-17082966
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Denys Kuzmenko edited comment on HIVE-21354 at 4/14/20, 8:17 AM:
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[~belugabehr], [~pvary], checkLock searches stuff hierarchically, so if you
have conflicting locks on any level (db/table/partition) - it's gonna backoff
and try later. Exception are: EXCLUSIVE on a table/partition shouldn't prevent
SHARED_READ on a database.
was (Author: dkuzmenko):
[~belugabehr], [~pvary], checkLock searches stuff hierarchically, so if you
have conflicting locks on any level (db/table/partition) - it's gonna backoff
and try later. Exception are EXCLUSIVE on a table shouldn't prevent SHARED_READ
on a database, similarly EXCLUSIVE on a partition should not conflict with
SHARED_READ on a database.
> Lock The Entire Table If Majority Of Partitions Are Locked
> ----------------------------------------------------------
>
> Key: HIVE-21354
> URL: https://issues.apache.org/jira/browse/HIVE-21354
> Project: Hive
> Issue Type: Improvement
> Components: HiveServer2
> Affects Versions: 4.0.0, 3.2.0
> Reporter: David Mollitor
> Assignee: David Mollitor
> Priority: Major
>
> One of the bottlenecks of any Hive query is the ZooKeeper locking mechanism.
> When a Hive query interacts with a table which has a lot of partitions, this
> may put a lot of stress on the ZK system.
> Please add a heuristic that works like this:
> # Count the number of partitions that a query is required to lock
> # Obtain the total number of partitions in the table
> # If the number of partitions accessed by the query is greater than or equal
> to half the total number of partitions, simply create one ZNode lock at the
> table level.
> This would improve performance of many queries, but in particular, a {{select
> count(1) from table}} ... or ... {{select * from table limit 5}} where the
> table has many partitions.
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