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https://issues.apache.org/jira/browse/HIVE-24710?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Rajesh Balamohan updated HIVE-24710:
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Summary: Optimise PTF iteration for count(*) to reduce CPU and IO cost
(was: PTFRowContainer could be reading more number of blocks than needed)
> Optimise PTF iteration for count(*) to reduce CPU and IO cost
> -------------------------------------------------------------
>
> Key: HIVE-24710
> URL: https://issues.apache.org/jira/browse/HIVE-24710
> Project: Hive
> Issue Type: Improvement
> Components: HiveServer2
> Reporter: Rajesh Balamohan
> Priority: Major
> Labels: performance
>
> PTFRowContainer could be reading the same block repeatedly for the first
> block. Default block size is around 25000. For the first 25000 rowIdx, it
> would read the block repeatedly due to ("rowIdx < currentReadBlockStartRow ")
> condition.
> {noformat}
> public Row getAt(int rowIdx) throws HiveException {
> int blockSize = getBlockSize();
> if ( rowIdx < currentReadBlockStartRow || rowIdx >=
> currentReadBlockStartRow + blockSize ) {
> readBlock(getBlockNum(rowIdx));
> }
> return getReadBlockRow(rowIdx - currentReadBlockStartRow);
> }
> {noformat}
> https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/PTFRowContainer.java#L167
>
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