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ASF GitHub Bot commented on DRILL-4387: --------------------------------------- GitHub user jinfengni opened a pull request: https://github.com/apache/drill/pull/379 DRILL-4387: GroupScan or ScanBatchCreator should not use star column … …in case of skipAll query. The skipAll query should be handled in RecordReader. You can merge this pull request into a Git repository by running: $ git pull https://github.com/jinfengni/incubator-drill DRILL-4387 Alternatively you can review and apply these changes as the patch at: https://github.com/apache/drill/pull/379.patch To close this pull request, make a commit to your master/trunk branch with (at least) the following in the commit message: This closes #379 ---- commit 5c1edc42dcad6c3b5943424b9a8373cf6ff51753 Author: Jinfeng Ni <j...@apache.org> Date: 2016-02-12T22:18:59Z DRILL-4387: GroupScan or ScanBatchCreator should not use star column in case of skipAll query. The skipAll query should be handled in RecordReader. ---- > Improve execution side when it handles skipAll query > ---------------------------------------------------- > > Key: DRILL-4387 > URL: https://issues.apache.org/jira/browse/DRILL-4387 > Project: Apache Drill > Issue Type: Bug > Reporter: Jinfeng Ni > Assignee: Jinfeng Ni > Fix For: 1.6.0 > > > DRILL-4279 changes the planner side and the RecordReader in the execution > side when they handles skipAll query. However, it seems there are other > places in the codebase that do not handle skipAll query efficiently. In > particular, in GroupScan or ScanBatchCreator, we will replace a NULL or empty > column list with star column. This essentially will force the execution side > (RecordReader) to fetch all the columns for data source. Such behavior will > lead to big performance overhead for the SCAN operator. > To improve Drill's performance, we should change those places as well, as a > follow-up work after DRILL-4279. > One simple example of this problem is: > {code} > SELECT DISTINCT substring(dir1, 5) from dfs.`/Path/To/ParquetTable`; > {code} > The query does not require any regular column from the parquet file. However, > ParquetRowGroupScan and ParquetScanBatchCreator will put star column as the > column list. In case table has dozens or hundreds of columns, this will make > SCAN operator much more expensive than necessary. -- This message was sent by Atlassian JIRA (v6.3.4#6332)