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https://issues.apache.org/jira/browse/HIVE-11954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14969935#comment-14969935
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Laljo John Pullokkaran commented on HIVE-11954:
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+1
> Extend logic to choose side table in MapJoin Conversion algorithm
> -----------------------------------------------------------------
>
> Key: HIVE-11954
> URL: https://issues.apache.org/jira/browse/HIVE-11954
> Project: Hive
> Issue Type: Bug
> Components: Physical Optimizer
> Affects Versions: 2.0.0
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
> Attachments: HIVE-11954.01.patch, HIVE-11954.02.patch,
> HIVE-11954.03.patch, HIVE-11954.04.patch, HIVE-11954.05.patch,
> HIVE-11954.06.patch, HIVE-11954.07.patch, HIVE-11954.08.patch,
> HIVE-11954.09.patch, HIVE-11954.10.patch, HIVE-11954.11.patch,
> HIVE-11954.12.patch, HIVE-11954.patch, HIVE-11954.patch
>
>
> Selection of side table (in memory/hash table) in MapJoin Conversion
> algorithm needs to be more sophisticated.
> In an N way Map Join, Hive should pick an input stream as side table (in
> memory table) that has least cost in producing relation (like TS(FIL|Proj)*).
> Cost based choice needs extended cost model; without return path its going to
> be hard to do this.
> For the time being we could employ a modified cost based algorithm for side
> table selection.
> New algorithm is described below:
> 1. Identify the candidate set of inputs for side table (in memory/hash table)
> from the inputs (based on conditional task size)
> 2. For each of the input identify its cost, memory requirement. Cost is 1 for
> each heavy weight relation op (Join, GB, PTF/Windowing, TF, etc.). Cost for
> an input is the total no of heavy weight ops in its branch.
> 3. Order set from #1 on cost & memory req (ascending order)
> 4. Pick the first element from #3 as the side table.
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