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From "Edward Capriolo (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-493) automatically infer existing partitions of table from HDFS files.
Date Tue, 14 Jul 2009 15:18:14 GMT

    [ https://issues.apache.org/jira/browse/HIVE-493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12730913#action_12730913

Edward Capriolo commented on HIVE-493:


by 'virtual read only schema' I mean that mysql has a schema table. You can run queries like

'select columns from table where tablename='tablea' '. Hive has some support for things like
'show partitions', but some data can only be read with the MetaStore API. 

For a use case. I want to write my compact utility. As a user I am faced with options on how
to do this. The best way would be a tightly integrated tool.
hive --service compact --table tablea
This tool would be smart. It would do things rebuild indexes, warn or error on external tables,
or bucketed columns.

On the other side of the spectrum one could write a map/reduce job with hard coded paths to
the warehouse that works on the file level this assumes I know a lot about the underpinning
of hive.

Users need to be able to explore the metastore table structure and the warehouse so their
utilities can make an informed decision. Should they link to the metastore API or should the
hql language support most of the operations and the process could be done purely from an HQL

> 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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