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From "Prasad Chakka (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-207) Change SerDe API to allow skipping unused columns
Date Thu, 08 Jan 2009 20:28:59 GMT

    [ https://issues.apache.org/jira/browse/HIVE-207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12662106#action_12662106
] 

Prasad Chakka commented on HIVE-207:
------------------------------------

another way of doing this is 

add a new function to SerDe interface that returns list of ColumnInfo (why DDL?) objects.
And provide a static utility method that takes a thrift DDL and converts to ColumnInfo/TypeInfo
classes and any serde that wants to use DDL in this form can call this function. Others needn't
do this.

> Change SerDe API to allow skipping unused columns
> -------------------------------------------------
>
>                 Key: HIVE-207
>                 URL: https://issues.apache.org/jira/browse/HIVE-207
>             Project: Hadoop Hive
>          Issue Type: Bug
>          Components: Query Processor, Serializers/Deserializers
>            Reporter: David Phillips
>
> A deserializer shouldn't have to deserialize columns that are never used by the query
processor.  A serializer shouldn't have to examine unused columns that are known to always
be null.
> As an example, we store data as a Protocol Buffer structure with ~60 fields.  Running
a "select count(1)" currently requires deserializing all fields, which includes checking if
they exist and formatting the data appropriately.  This is expensive and unnecessary.

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