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From "Zheng Shao (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-266) Improve SerDe performance by using Text instead of String
Date Tue, 31 Mar 2009 23:03:50 GMT

    [ https://issues.apache.org/jira/browse/HIVE-266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12694315#action_12694315

Zheng Shao commented on HIVE-266:

We had a discussion yesterday:

* Logical Data Types
** Used for defining table columns
** Example: String, Integer
* Physical Data Types
** Used for Internal Processing
** Examples: String/Text, Integer/IntWritable

* Efficiency
** Text is reusable
** Text is UTF-8
** Usually the same as serialized format
* Standard:
** Text is Hadoop standard
** String is Java standard
** Will be useful to interface with Thrift, ProtocolBuffer etc

* Now:
** Everything is String (and Integer)
* Future:
** Choice 1: Use only Text (and IntWritable)
*** How to interface with Thrift and other standard Java libraries?
** Choice 2: Use a combination of String/Text (and Integer/IntWritable)
*** Ideal case
*** Much more complicated: PhysicalDataTypes will change after SerDe (ReduceSinkOperator or

The conclusion is that we will go Choice 1: Replace String/Integer etc in Hive with Text/IntWritable.
As a side-effect, all SerDe/UDF(including UDAF) needs to use Writables instead of Java Primitive

We will change hive internal SerDe/UDF functions.  For user-defined SerDe/UDFs, users will
need to change them to make them work with Hive 0.4.

> Improve SerDe performance by using Text instead of String
> ---------------------------------------------------------
>                 Key: HIVE-266
>                 URL: https://issues.apache.org/jira/browse/HIVE-266
>             Project: Hadoop Hive
>          Issue Type: Improvement
>          Components: Serializers/Deserializers
>    Affects Versions: 0.2.0
>            Reporter: Zheng Shao
>            Priority: Critical
> A recent performance study showed that 2 places in Hive code has exhibited large cpu
usage percentage:
> 1. String.getBytes() (UTF-8 encoding)
> 2. String.split()
> We should replace String with Text object to:
> 1. Avoid UTF-8 decoding and encoding
> 2. Reuse the Text object and avoid creating new objects for each column in each row like
in String.split()
> This is expected to give a big (20%+) performance improvement to Hive.

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