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Posted to dev@hive.apache.org by "Namit Jain (Created) (JIRA)" <ji...@apache.org> on 2012/03/07 02:39:57 UTC
[jira] [Created] (HIVE-2847) Add support for query rewrite from the
metadata
Add support for query rewrite from the metadata
-----------------------------------------------
Key: HIVE-2847
URL: https://issues.apache.org/jira/browse/HIVE-2847
Project: Hive
Issue Type: New Feature
Reporter: Namit Jain
A simple query like:
select count(1) from T
should be able to get the results from the metadata instead of scanning the complete input table T.
2. the metadata only queries today does not scale to a very large number of partitions - that needs to be fixed.
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[jira] [Commented] (HIVE-2847) Add support for query rewrite from
the metadata
Posted by "Namit Jain (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/jira/browse/HIVE-2847?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13461442#comment-13461442 ]
Namit Jain commented on HIVE-2847:
----------------------------------
Few parameters,like hive.stats.reliable, have been introduced to figure out if stats are accurate.
The idea behind this jira is to use the stats from the metadata to rewrite some queries.
For eg: for queries like
select count(1) from T where ds > 10;
Say, partitions T@ds=11 and T@ds=12 satisfy the query.
If number of rows are present in the metadata for T@ds=11, T@ds=12, there is no need to scan the data to get the results.
> Add support for query rewrite from the metadata
> -----------------------------------------------
>
> Key: HIVE-2847
> URL: https://issues.apache.org/jira/browse/HIVE-2847
> Project: Hive
> Issue Type: New Feature
> Reporter: Namit Jain
> Labels: gsoc, gsoc2012
>
> A simple query like:
> select count(1) from T
> should be able to get the results from the metadata instead of scanning the complete input table T.
> 2. the metadata only queries today does not scale to a very large number of partitions - that needs to be fixed.
--
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If you think it was sent incorrectly, please contact your JIRA administrators
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[jira] [Commented] (HIVE-2847) Add support for query rewrite from
the metadata
Posted by "Namit Jain (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/jira/browse/HIVE-2847?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13461445#comment-13461445 ]
Namit Jain commented on HIVE-2847:
----------------------------------
This will require a number of issues to be fixed:
1. Metadata needs to be maintained at the partition level whether the stats for that partition are accurate or not.
2. As more column level statistics are being added, the existing infrastructure should be used to support queries like:
select max(x) from T
where column level statistics are stored for 'x'
This jira can either be extended to support column level stats, or can propose a format to store column level stats, and then use them for
query rewrite.
> Add support for query rewrite from the metadata
> -----------------------------------------------
>
> Key: HIVE-2847
> URL: https://issues.apache.org/jira/browse/HIVE-2847
> Project: Hive
> Issue Type: New Feature
> Reporter: Namit Jain
> Labels: gsoc, gsoc2012
>
> A simple query like:
> select count(1) from T
> should be able to get the results from the metadata instead of scanning the complete input table T.
> 2. the metadata only queries today does not scale to a very large number of partitions - that needs to be fixed.
--
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