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From "Joydeep Sen Sarma (JIRA)" <>
Subject [jira] Commented: (HIVE-207) Change SerDe API to allow skipping unused columns
Date Mon, 05 Jan 2009 23:33:44 GMT


Joydeep Sen Sarma commented on HIVE-207:

@Zheng - can we get lazy deserialization using Dynamic Serde without changing the Dynamic
Serde code (and writing a new protocol only?)?

alternatively - we could ignore the whole DDL thing right now and create a table with a custom
serde for protocol buffers and put the schema information in the serde properties (which the
create table command should support).

Instead of forcing people to use dynamic serde (when they want to use DDL) - one extensibility
hook we can add is to generate serde configuration from the parsed DDL information using a
callback. Perhaps this can be an optional method in the SerDe. That way - people can add Hive
DDL to Protocol Buffer configuration (for example) without having to use Dynamic Serde.

> Change SerDe API to allow skipping unused columns
> -------------------------------------------------
>                 Key: HIVE-207
>                 URL:
>             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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