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From "Schubert Zhang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-493) automatically infer existing partitions of table from HDFS files.
Date Mon, 28 Sep 2009 17:55:16 GMT

    [ https://issues.apache.org/jira/browse/HIVE-493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12760312#action_12760312

Schubert Zhang commented on HIVE-493:


1) We want the data to be available in the Hive table after each run of the MapReduce job.
Do you mean we should only 'add partition' once at the first time? and need not do it after
add new files into a existing partition?

2) Thanks for your good advices. The lease is necessary.

It seems we (you and we) should add more features into Hive and let Hive to be a data server
(or data warehouse server), since current Hive is a dumb data tool to translate HQL to MapReduce.

When thinking of following important data service features, such as:
- Indexing
- Compact
- Lease
- Real Dyanmic Partition (or automatic partition ,even varying partition)
- ....

It seems, besides MapReduce data processing and SQL, we shall implement a light and flexiable
BigTable/HBase like data service solution.

> automatically infer existing partitions of table from HDFS files.
> -----------------------------------------------------------------
>                 Key: HIVE-493
>                 URL: https://issues.apache.org/jira/browse/HIVE-493
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Metastore, Query Processor
>    Affects Versions: 0.3.0, 0.3.1, 0.4.0
>            Reporter: Prasad Chakka
> Initially partition list for a table is inferred from HDFS directory structure instead
of looking into metastore (partitions are created using 'alter table ... add partition').
but this automatic inferring was removed to favor the later approach during checking-in metastore
checker feature and also to facilitate external partitions.
> Joydeep and Frederick mentioned that it would simple for users to create the HDFS directory
and let Hive infer rather than explicitly add a partition. But doing that raises following...
> 1) External partitions -- so we have to mix both approaches and partition list is merged
list of inferred partitions and registered partitions. and duplicates have to be resolved.
> 2) Partition level schemas can't supported. Which schema to chose for the inferred partitions?
the table schema when the inferred partition is created or the latest tale schema? how do
we know the table schema when the inferred partitions is created?
> 3) If partitions have to be registered the partitions can be disabled without actually
deleting the data. this feature is not supported and may not be that useful but nevertheless
this can't be supported with inferred partitions
> 4) Indexes are being added. So if partitions are not registered then indexes for such
partitions can not be maintained automatically.
> I would like to know what is the general thinking about this among users of Hive. If
inferred partitions are preferred then can we live with restricted functionality that this

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