[
https://issues.apache.org/jira/browse/HIVE-105?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12666354#action_12666354
]
Zheng Shao commented on HIVE-105:
---------------------------------
It seems we still need some discussion or commit the infrastructure before Part
B can be done.
What about committing Part A by itself and open a new Jira for Part B?
Part A is self-complete in that:
1. If the user set the number of reducers (through mapred.reduce.tasks), Hive
will do exactly it does before.
2. If the user does not, then Hive will automatically figure out the number of
reducers for each phase.
1 also makes sure the user can always make Hive behave like before.
> estimate number of required reducers and other map-reduce parameters
> automatically
> ----------------------------------------------------------------------------------
>
> Key: HIVE-105
> URL: https://issues.apache.org/jira/browse/HIVE-105
> Project: Hadoop Hive
> Issue Type: Improvement
> Components: Query Processor
> Reporter: Joydeep Sen Sarma
> Assignee: Zheng Shao
> Attachments: HIVE-105.1.patch
>
>
> currently users have to specify number of reducers. In a multi-user
> environment - we generally ask users to be prudent in selecting number of
> reducers (since they are long running and block other users). Also - large
> number of reducers produce large number of output files - which puts pressure
> on namenode resources.
> there are other map-reduce parameters - for example the min split size and
> the proposed use of combinefileinputformat that are also fairly tricky for
> the user to determine (since they depend on map side selectivity and cluster
> size). This will become totally critical when there is integration with BI
> tools since there will be no opportunity to optimize job settings and there
> will be a wide variety of jobs.
> This jira calls for automating the selection of such parameters - possibly by
> a best effort at estimating map side selectivity/output size using sampling
> and determining such parameters from there.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
