[jira] [Commented] (DRILL-4735) Count(dir0) on parquet returns 0 result

["Arina Ielchiieva (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-4735?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16089662#comment-16089662 ] 

Arina Ielchiieva commented on DRILL-4735:
-----------------------------------------

Fix will cover the following aspects:

1. {{ConvertCountToDirectScan}} will be able to distinguish between implicit / directory and non-existent columns, relates to current Jira DRILL-4735.
To achieve this `Agg_on_scan` and `Agg_on_proj_on_scan` rules will take new parameter in constructor {{OptimizerRulesContext}}, similar for [prune scan rules|https://github.com/apache/drill/blob/3e8b01d5b0d3013e3811913f0fd6028b22c1ac3f/exec/java-exec/src/main/java/org/apache/drill/exec/planner/PlannerPhase.java#L345]. It will help to find out if column is implicit / directory or not. {{OptimizerRulesContext}} has access to session options through {{PlannerSettings}} which are crucial for defining current implicit / directory column names. In case when [GroupScan will return column value as 0|https://github.com/apache/drill/blob/3e8b01d5b0d3013e3811913f0fd6028b22c1ac3f/exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/ConvertCountToDirectScan.java#L140], we'll check if this column implicit / directory or not.  If not, we'll proceed with applying our rule.

2. {{ConvertCountToDirectScan}} rule to be applicable for 2 or more COUNT aggregates, relates to DRILL-1691.
When column statistics is available we use {{PojoRecordReader}} to return its value. {{PojoRecordReader}} requires exact model. In our case we'll need reader that will allow dynamic model usage (the one where we don't know how many columns it will have). For this purpose {{DynamicPojoRecordReader}} will be used. Instead of exact model it will accept dynamic model represented by {{List<LinkedHashMap<String, Object>> records}}, list of maps where key -> column name, value -> column value. Common logic between  {{PojoRecordReader}} and {{DynamicPojoRecordReader}} will extracted in abstract parent class.

3. Currently when {{ConvertCountToDirectScan}} is applied in plan we see the following:
{noformat}
Scan(groupscan=[org.apache.drill.exec.store.pojo.PojoRecordReader@60017daf[columns = null, isStarQuery = false, isSkipQuery = false]])
{noformat}
User has no idea that column statistics was used to calculate the result, if partition pruning took place etc, relates to DRILL-5357 and DRILL-3407.
Currently we use {{DirectGroupScan}} to hold our record reader. To include more information we'll extend {{DirectGroupScan}} to {{MetadataDirectGroupScan}} which will contain information about read files if any. Also {{PojoRecordReader}} and {{DirectPojoRecordReader}} {{toString}} methods will be overridden to show meaningful information to the user.
Example:
{noformat}
Scan(groupscan=[usedMetadata = true, files = [/tpch/nation.parquet], DynamicPojoRecordReader{records=[{count0=25, count1=25, count2=25}]}])
{noformat}



> Count(dir0) on parquet returns 0 result
> ---------------------------------------
>
>                 Key: DRILL-4735
>                 URL: https://issues.apache.org/jira/browse/DRILL-4735
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Query Planning & Optimization, Storage - Parquet
>    Affects Versions: 1.0.0, 1.4.0, 1.6.0, 1.7.0
>            Reporter: Krystal
>            Assignee: Arina Ielchiieva
>            Priority: Critical
>
> Selecting a count of dir0, dir1, etc against a parquet directory returns 0 rows.
> select count(dir0) from `min_max_dir`;
> +---------+
> | EXPR$0  |
> +---------+
> | 0       |
> +---------+
> select count(dir1) from `min_max_dir`;
> +---------+
> | EXPR$0  |
> +---------+
> | 0       |
> +---------+
> If I put both dir0 and dir1 in the same select, it returns expected result:
> select count(dir0), count(dir1) from `min_max_dir`;
> +---------+---------+
> | EXPR$0  | EXPR$1  |
> +---------+---------+
> | 600     | 600     |
> +---------+---------+
> Here is the physical plan for count(dir0) query:
> {code}
> 00-00    Screen : rowType = RecordType(BIGINT EXPR$0): rowcount = 20.0, cumulative cost = {22.0 rows, 22.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1346
> 00-01      Project(EXPR$0=[$0]) : rowType = RecordType(BIGINT EXPR$0): rowcount = 20.0, cumulative cost = {20.0 rows, 20.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1345
> 00-02        Project(EXPR$0=[$0]) : rowType = RecordType(BIGINT EXPR$0): rowcount = 20.0, cumulative cost = {20.0 rows, 20.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1344
> 00-03          Scan(groupscan=[org.apache.drill.exec.store.pojo.PojoRecordReader@3da85d3b[columns = null, isStarQuery = false, isSkipQuery = false]]) : rowType = RecordType(BIGINT count): rowcount = 20.0, cumulative cost = {20.0 rows, 20.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1343
> {code}
> Here is part of the explain plan for the count(dir0) and count(dir1) in the same select:
> {code}
> 00-00    Screen : rowType = RecordType(BIGINT EXPR$0, BIGINT EXPR$1): rowcount = 60.0, cumulative cost = {1206.0 rows, 15606.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1623
> 00-01      Project(EXPR$0=[$0], EXPR$1=[$1]) : rowType = RecordType(BIGINT EXPR$0, BIGINT EXPR$1): rowcount = 60.0, cumulative cost = {1200.0 rows, 15600.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1622
> 00-02        StreamAgg(group=[{}], EXPR$0=[COUNT($0)], EXPR$1=[COUNT($1)]) : rowType = RecordType(BIGINT EXPR$0, BIGINT EXPR$1): rowcount = 60.0, cumulative cost = {1200.0 rows, 15600.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1621
> 00-03          Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath [path=maprfs:/drill/testdata/min_max_dir/1999/Apr/voter20.parquet/0_0_0.parquet], ReadEntryWithPath [path=maprfs:/drill/testdata/min_max_dir/1999/MAR/voter15.parquet/0_0_0.parquet], ReadEntryWithPath [path=maprfs:/drill/testdata/min_max_dir/1985/jan/voter5.parquet/0_0_0.parquet], ReadEntryWithPath [path=maprfs:/drill/testdata/min_max_dir/1985/apr/voter60.parquet/0_0_0.parquet],..., ReadEntryWithPath [path=maprfs:/drill/testdata/min_max_dir/2014/jul/voter35.parquet/0_0_0.parquet]], selectionRoot=maprfs:/drill/testdata/min_max_dir, numFiles=16, usedMetadataFile=false, columns=[`dir0`, `dir1`]]]) : rowType = RecordType(ANY dir0, ANY dir1): rowcount = 600.0, cumulative cost = {600.0 rows, 1200.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1620
> {code}
> Notice that in the first case, "org.apache.drill.exec.store.pojo.PojoRecordReader" is used.



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