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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-4196) Support for Streaming Partitions in Hive
Date Fri, 19 Jul 2013 23:46:48 GMT

    [ https://issues.apache.org/jira/browse/HIVE-4196?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13714235#comment-13714235
] 

Alan Gates commented on HIVE-4196:
----------------------------------

Some comments:

According to the Hive coding conventions lines should be bounded at 100 characters.  Many
lines in this patch exceed that.

In ObjectStore.java:
* I'm surprised to see that streamingStatus sets the chunk id for the table.  This seems to
be a status call.  Why should it be setting chunk id?
* The logic at the end of of these functions doesn't look right.  Take getNextChunkID for
example.  If commitTransaction fails (line 2132) rollback will be called but the next chunk
id will still be returned.  It seems you need a check on success after commit.  I realize
many of the calls in the class follow this, but it doesn't seem right.

In HiveMetaStoreClient.java, is assert what you want?  Are you ok with the validity of the
arguments not being checked most of the time?

I'm trying to figure out whether the chunk files are moved, deleted, or left alone during
the partition rolling.  From examining the code and playing with Hive it looks like the files
will be left alone.  But have you tested this?

Which leads to, I don't see any tests in this patch.  This code needs a lot of tests.

                
> Support for Streaming Partitions in Hive
> ----------------------------------------
>
>                 Key: HIVE-4196
>                 URL: https://issues.apache.org/jira/browse/HIVE-4196
>             Project: Hive
>          Issue Type: New Feature
>          Components: Database/Schema, HCatalog
>    Affects Versions: 0.10.1
>            Reporter: Roshan Naik
>            Assignee: Roshan Naik
>         Attachments: HCatalogStreamingIngestFunctionalSpecificationandDesign- apr 29-
patch1.docx, HCatalogStreamingIngestFunctionalSpecificationandDesign- apr 29- patch1.pdf,
HIVE-4196.v1.patch
>
>
> Motivation: Allow Hive users to immediately query data streaming in through clients such
as Flume.
> Currently Hive partitions must be created after all the data for the partition is available.
Thereafter, data in the partitions is considered immutable. 
> This proposal introduces the notion of a streaming partition into which new files an
be committed periodically and made available for queries before the partition is closed and
converted into a standard partition.
> The admin enables streaming partition on a table using DDL. He provides the following
pieces of information:
> - Name of the partition in the table on which streaming is enabled
> - Frequency at which the streaming partition should be closed and converted into a standard
partition.
> Tables with streaming partition enabled will be partitioned by one and only one column. It
is assumed that this column will contain a timestamp.
> Closing the current streaming partition converts it into a standard partition. Based
on the specified frequency, the current streaming partition  is closed and a new one created
for future writes. This is referred to as 'rolling the partition'.
> A streaming partition's life cycle is as follows:
>  - A new streaming partition is instantiated for writes
>  - Streaming clients request (via webhcat) for a HDFS file name into which they can write
a chunk of records for a specific table.
>  - Streaming clients write a chunk (via webhdfs) to that file and commit it(via webhcat).
Committing merely indicates that the chunk has been written completely and ready for serving
queries.  
>  - When the partition is rolled, all committed chunks are swept into single directory
and a standard partition pointing to that directory is created. The streaming partition is
closed and new streaming partition is created. Rolling the partition is atomic. Streaming
clients are agnostic of partition rolling.  
>  - Hive queries will be able to query the partition that is currently open for streaming.
only committed chunks will be visible. read consistency will be ensured so that repeated reads
of the same partition will be idempotent for the lifespan of the query.
> Partition rolling requires an active agent/thread running to check when it is time to
roll and trigger the roll. This could be either be achieved by using an external agent such
as Oozie (preferably) or an internal agent.

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