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From "Ashutosh Chauhan (JIRA)" <>
Subject [jira] [Commented] (HIVE-4838) Refactor MapJoin HashMap code to improve testability and readability
Date Wed, 10 Jul 2013 17:57:49 GMT


Ashutosh Chauhan commented on HIVE-4838:

I am glad you are taking a stab at this Brock. I looked at it couple of days and immediately
felt the need for refactor. I was looking at it from performance point of view. There are
couple of things which are worth considering in this refactor. 
* We are using java serialization to serialize the hash table. If we use some custom serialization
we can possibly increase both memory efficiency as well as speed for this piece of code.
* Keys & values of the map are wrapper java objects, if we can use better data structures
that will be further win.

I am just putting up as thoughts which came to my mind in 15 mins perusal of that class. Feel
free to ignore them for now, we can take these latter once this basic cleanup is in.
> Refactor MapJoin HashMap code to improve testability and readability
> --------------------------------------------------------------------
>                 Key: HIVE-4838
>                 URL:
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Brock Noland
>            Assignee: Brock Noland
> MapJoin is an essential component for high performance joins in Hive and the current
code has done great service for many years. However, the code is showing it's age and currently
suffers  from the following issues:
> * Uses static state via the MapJoinMetaData class to pass serialization metadata to the
Key, Row classes.
> * The api of a logical "Table Container" is not defined and therefore it's unclear what
apis HashMapWrapper 
> needs to publicize. Additionally HashMapWrapper has many used public methods.
> * HashMapWrapper contains logic to serialize, test memory bounds, and implement the table
container. Ideally these logical units could be seperated
> * HashTableSinkObjectCtx has unused fields and unused methods
> * CommonJoinOperator and children use ArrayList on left hand side when only List is required
> * There are unused classes MRU, DCLLItemm, MapJoinSingleKey, and MapJoinDoubleKeys

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