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From "Sohan Jain" <sohanj...@fb.com>
Subject Re: Review Request: HIVE-2246: Dedupe tables' column schemas from partitions in the metastore db
Date Sat, 06 Aug 2011 01:41:58 GMT

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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/1183/#review1313
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trunk/metastore/src/java/org/apache/hadoop/hive/metastore/ObjectStore.java
<https://reviews.apache.org/r/1183/#comment2984>

    should read 1-N actually


- Sohan


On 2011-08-06 01:40:49, Sohan Jain wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/1183/
> -----------------------------------------------------------
> 
> (Updated 2011-08-06 01:40:49)
> 
> 
> Review request for hive, Ning Zhang and Paul Yang.
> 
> 
> Summary
> -------
> 
> This patch tries to make minimal changes to the API while keeping migration short and
somewhat easy to revert.
> 
> The new schema can be described as follows:
> - CDS is a table corresponding to Column Descriptor objects.  Currently, it only stores
a CD_ID.
> - COLUMNS_V2 is a table corresponding to MFieldSchema objects, or columns.  A Column
Descriptor holds a list of columns.  COLUMNS_V2 has a foreign key to the CD_ID to which it
belongs.
> - SDS was modified to reference a Column Descriptor. So SDS now has a foreign key to
a CD_ID which describes its columns.
> 
> During migration, we create Column Descriptors for tables in a straightforward manner:
their columns are now just wrapped inside a column descriptor.  The SDS of partitions use
their parent table's column descriptor, since currently a partition and its table share the
same list of columns.
> 
> When altering or adding a partition, give it it's parent table's column descriptor IF
the columns they describe are the same.  Otherwise, create a new column descriptor for its
columns.
> 
> When adding or altering a table, create a new column descriptor every time.
> 
> Whenever you drop a storage descriptor (e.g, when dropping tables or partitions), check
to see if the related column descriptor has any other references in the table.  That is, check
to see if any other storage descriptors point to that column descriptor.  If none do, then
delete that column descriptor.  This check is in place so we don't have unreferenced column
descriptors and columns hanging around after schema evolution for tables.
> 
> 
> This addresses bug HIVE-2246.
>     https://issues.apache.org/jira/browse/HIVE-2246
> 
> 
> Diffs
> -----
> 
>   trunk/metastore/scripts/upgrade/mysql/008-HIVE-2246.mysql.sql PRE-CREATION 
>   trunk/metastore/src/java/org/apache/hadoop/hive/metastore/HiveMetaStore.java 1153927

>   trunk/metastore/src/java/org/apache/hadoop/hive/metastore/ObjectStore.java 1153927

>   trunk/metastore/src/model/org/apache/hadoop/hive/metastore/model/MColumnDescriptor.java
PRE-CREATION 
>   trunk/metastore/src/model/org/apache/hadoop/hive/metastore/model/MStorageDescriptor.java
1153927 
>   trunk/metastore/src/model/package.jdo 1153927 
>   trunk/ql/src/java/org/apache/hadoop/hive/ql/exec/DDLTask.java 1153927 
>   trunk/ql/src/java/org/apache/hadoop/hive/ql/metadata/MetaDataFormatUtils.java 1153927

> 
> Diff: https://reviews.apache.org/r/1183/diff
> 
> 
> Testing
> -------
> 
> Passes facebook's regression testing and all existing test cases.  In one instance, before
migration, the overhead involved with storage descriptors and columns was ~11 GB.  After migration,
the overhead was ~1.5 GB.
> 
> 
> Thanks,
> 
> Sohan
> 
>


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