[jira] Commented: (HIVE-493) automatically infer existing partitions of table from HDFS files.

["Schubert Zhang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12760290#action_12760290 ] 

Schubert Zhang commented on HIVE-493:
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We have following use case:

1. We have a periodic MapReduce job to pre-process the source data (files) and want put the output data files into HDFS directory. The HDFS directory is correspond to a Hive table (this table should be partitioned).  The above MapReduce job shall output data into different partitions based on data analysis.

2. We want Hive to recognise any new raised partitions from HDFS sub-directories under the table's root directory. And the above MapReduce job may add new files into new created partitions or existing partitions.

3. We also need a compact/merging process to periodic compact or merge the existing partitions to get bigger files.

> 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 imposes?

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