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https://issues.apache.org/jira/browse/DRILL-6118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16375185#comment-16375185
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ASF GitHub Bot commented on DRILL-6118:
---------------------------------------

Github user amansinha100 commented on the issue:

    https://github.com/apache/drill/pull/1104
  
    +1


> Handle item star columns during project  /  filter push down and directory 
> pruning
> ----------------------------------------------------------------------------------
>
>                 Key: DRILL-6118
>                 URL: https://issues.apache.org/jira/browse/DRILL-6118
>             Project: Apache Drill
>          Issue Type: Improvement
>    Affects Versions: 1.12.0
>            Reporter: Arina Ielchiieva
>            Assignee: Arina Ielchiieva
>            Priority: Major
>              Labels: doc-impacting, ready-to-commit
>             Fix For: 1.13.0
>
>
> Project push down, filter push down and partition pruning does not work with 
> dynamically expanded column with is represented as star in ITEM operator: 
> _ITEM($0, 'column_name')_ where $0 is a star.
>  This often occurs when view, sub-select or cte with star is issued.
>  To solve this issue we can create {{DrillFilterItemStarReWriterRule}} which 
> will rewrite such ITEM operator before filter push down and directory 
> pruning. For project into scan push down logic will be handled separately in 
> already existing rule {{DrillPushProjectIntoScanRule}}. Basically, we can 
> consider the following queries the same: 
>  {{select col1 from t}}
>  {{select col1 from (select * from t)}}
> *Use cases*
> Since item star columns where not considered during project / filter push 
> down and directory pruning, push down and pruning did not happen. This was 
> causing Drill to read all columns from file (when only several are needed) or 
> ready all files instead. Views with star query is the most common example. 
> Such behavior significantly degrades performance for item star queries 
> comparing to queries without item star.
> *EXAMPLES*
> *Data set* 
> will create table with three files each in dedicated sub-folder:
> {noformat}
> use dfs.tmp;
> create table `order_ctas/t1` as select cast(o_orderdate as date) as 
> o_orderdate from cp.`tpch/orders.parquet` where o_orderdate between date 
> '1992-01-01' and date '1992-01-03';
> create table `order_ctas/t2` as select cast(o_orderdate as date) as 
> o_orderdate from cp.`tpch/orders.parquet` where o_orderdate between date 
> '1992-01-04' and date '1992-01-06';
> create table `order_ctas/t3` as select cast(o_orderdate as date) as 
> o_orderdate from cp.`tpch/orders.parquet` where o_orderdate between date 
> '1992-01-07' and date '1992-01-09';
> {noformat}
> *Filter push down*
> {{select * from order_ctas where o_orderdate = date '1992-01-01'}} will read 
> only one file
> {noformat}
> 00-00    Screen
> 00-01      Project(**=[$0])
> 00-02        Project(T1¦¦**=[$0])
> 00-03          SelectionVectorRemover
> 00-04            Filter(condition=[=($1, 1992-01-01)])
> 00-05              Project(T1¦¦**=[$0], o_orderdate=[$1])
> 00-06                Scan(groupscan=[ParquetGroupScan 
> [entries=[ReadEntryWithPath [path=/tmp/order_ctas/t1/0_0_0.parquet]], 
> selectionRoot=/tmp/order_ctas, numFiles=1, numRowGroups=1, 
> usedMetadataFile=false, columns=[`**`]]])
> {noformat}
> {{select * from (select * from order_ctas) where o_orderdate = date 
> '1992-01-01'}} will ready all three files
> {noformat}
> 00-00    Screen
> 00-01      Project(**=[$0])
> 00-02        SelectionVectorRemover
> 00-03          Filter(condition=[=(ITEM($0, 'o_orderdate'), 1992-01-01)])
> 00-04            Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath 
> [path=/tmp/order_ctas/t1/0_0_0.parquet], ReadEntryWithPath 
> [path=/tmp/order_ctas/t2/0_0_0.parquet], ReadEntryWithPath 
> [path=/tmp/order_ctas/t3/0_0_0.parquet]], selectionRoot=/tmp/order_ctas, 
> numFiles=3, numRowGroups=3, usedMetadataFile=false, columns=[`**`]]])
> {noformat}
> *Directory pruning*
> {{select * from order_ctas where dir0 = 't1'}} will read data only from one 
> folder
> {noformat}
> 00-00    Screen
> 00-01      Project(**=[$0])
> 00-02        Project(**=[$0])
> 00-03          Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath 
> [path=/tmp/order_ctas/t1/0_0_0.parquet]], selectionRoot=/tmporder_ctas, 
> numFiles=1, numRowGroups=1, usedMetadataFile=false, columns=[`**`]]])
> {noformat}
> {{select * from (select * from order_ctas) where dir0 = 't1'}} will read 
> content of all three folders
> {noformat}
> 00-00    Screen
> 00-01      Project(**=[$0])
> 00-02        SelectionVectorRemover
> 00-03          Filter(condition=[=(ITEM($0, 'dir0'), 't1')])
> 00-04            Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath 
> [path=/tmp/order_ctas/t1/0_0_0.parquet], ReadEntryWithPath 
> [path=/tmp/order_ctas/t2/0_0_0.parquet], ReadEntryWithPath 
> [path=/tmp/order_ctas/t3/0_0_0.parquet]], selectionRoot=/tmp/order_ctas, 
> numFiles=3, numRowGroups=3, usedMetadataFile=false, columns=[`**`]]])
> {noformat}
> *Project into Scan push down*
> {{select o_orderdate, count(1) from order_ctas group by o_orderdate}} will 
> ready only one column from the files
> {noformat}
> 00-00    Screen
> 00-01      Project(o_orderdate=[$0], EXPR$1=[$1])
> 00-02        HashAgg(group=[{0}], EXPR$1=[COUNT()])
> 00-03          Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath 
> [path=/tmp/order_ctas/t1/0_0_0.parquet], ReadEntryWithPath 
> [path=/tmp/order_ctas/t2/0_0_0.parquet], ReadEntryWithPath 
> [path=/tmp/order_ctas/t3/0_0_0.parquet]], selectionRoot=/tmp/order_ctas, 
> numFiles=3, numRowGroups=3, usedMetadataFile=false, columns=[`o_orderdate`]]])
> {noformat}
> {{select o_orderdate, count(1) from (select * from order_ctas) group by 
> o_orderdate}} will ready all columns from the files
> {noformat}
> 00-00    Screen
> 00-01      Project(col_vrchr=[$0], EXPR$1=[$1])
> 00-02        StreamAgg(group=[{0}], EXPR$1=[COUNT()])
> 00-03          Sort(sort0=[$0], dir0=[ASC])
> 00-04            Project(col_vrchr=[ITEM($0, 'o_orderdate')])
> 00-05         Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath 
> [path=/tmp/order_ctas/t1/0_0_0.parquet], ReadEntryWithPath 
> [path=/tmp/order_ctas/t2/0_0_0.parquet], ReadEntryWithPath 
> [path=/tmp/order_ctas/t3/0_0_0.parquet]], selectionRoot=/tmp/order_ctas, 
> numFiles=3, numRowGroups=3, usedMetadataFile=false, columns=[`**`]]])
> {noformat}
> This Jira aims to fix all three described cases above in order to improve 
> performance for queries with item star columns.
>  



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