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https://issues.apache.org/jira/browse/HIVE-10793?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14560459#comment-14560459
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Lefty Leverenz commented on HIVE-10793:
---------------------------------------
Doc note: This changes the default value of
*hive.mapjoin.optimized.hashtable.wbsize* so the wiki needs to be updated (with
version information).
* [Configuration Properties -- hive.mapjoin.optimized.hashtable.wbsize |
https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-hive.mapjoin.optimized.hashtable.wbsize]
The patch also makes minor changes to the definitions of
*hive.mapjoin.hybridgrace.minwbsize* and
*hive.mapjoin.hybridgrace.minnumpartitions* which do not need any doc changes.
> Hybrid Hybrid Grace Hash Join : Don't allocate all hash table memory upfront
> ----------------------------------------------------------------------------
>
> Key: HIVE-10793
> URL: https://issues.apache.org/jira/browse/HIVE-10793
> Project: Hive
> Issue Type: Bug
> Components: Hive
> Affects Versions: 1.2.0
> Reporter: Mostafa Mokhtar
> Assignee: Mostafa Mokhtar
> Fix For: 1.3.0
>
> Attachments: HIVE-10793.1.patch, HIVE-10793.2.patch
>
>
> HybridHashTableContainer will allocate memory based on estimate, which means
> if the actual is less than the estimate the allocated memory won't be used.
> Number of partitions is calculated based on estimated data size
> {code}
> numPartitions = calcNumPartitions(memoryThreshold, estimatedTableSize,
> minNumParts, minWbSize,
> nwayConf);
> {code}
> Then based on number of partitions writeBufferSize is set
> {code}
> writeBufferSize = (int)(estimatedTableSize / numPartitions);
> {code}
> Each hash partition will allocate 1 WriteBuffer, with no further allocation
> if the estimate data size is correct.
> Suggested solution is to reduce writeBufferSize by a factor such that only X%
> of the memory is preallocated.
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