You are viewing a plain text version of this content. The canonical link for it is here.
Posted to issues@drill.apache.org by "Bridget Bevens (JIRA)" <ji...@apache.org> on 2018/04/16 21:17:00 UTC
[jira] [Commented] (DRILL-6118) Handle item star columns during
project / filter push down and directory pruning
[ https://issues.apache.org/jira/browse/DRILL-6118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16440040#comment-16440040 ]
Bridget Bevens commented on DRILL-6118:
---------------------------------------
Documentation is updated for this JIRA: [https://drill.apache.org/docs/parquet-filter-pushdown/]
> 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.
>
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)