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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4679) CONVERT_FROM() json format fails if 0 rows are received from upstream operator
Date Fri, 20 May 2016 15:56:13 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4679?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15293596#comment-15293596
] 

ASF GitHub Bot commented on DRILL-4679:
---------------------------------------

Github user jinfengni commented on a diff in the pull request:

    https://github.com/apache/drill/pull/504#discussion_r64064412
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/project/ProjectRecordBatch.java
---
    @@ -136,6 +145,10 @@ public VectorContainer getOutgoingContainer() {
     
       @Override
       protected IterOutcome doWork() {
    +    if (wasNone) {
    +      return IterOutcome.NONE;
    +    }
    +
         int incomingRecordCount = incoming.getRecordCount();
     
         if (first && incomingRecordCount == 0) {
    --- End diff --
    
    The new logic will handle the case for Project's first outgoing batch. Not sure whether
Drill works properly after the first batch getting data and building the schema, but the next
incoming batch contains empty result. We may treat as a separate issue for further investigation.




> CONVERT_FROM()  json format fails if 0 rows are received from upstream operator
> -------------------------------------------------------------------------------
>
>                 Key: DRILL-4679
>                 URL: https://issues.apache.org/jira/browse/DRILL-4679
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Execution - Relational Operators
>    Affects Versions: 1.6.0
>            Reporter: Aman Sinha
>            Assignee: Jinfeng Ni
>
> CONVERT_FROM() json format fails as below if the underlying Filter produces 0 rows: 
> {noformat}
> 0: jdbc:drill:zk=local> select convert_from('{"abc":"xyz"}', 'json') as x from cp.`tpch/region.parquet`
where r_regionkey = 9999;
> Error: SYSTEM ERROR: IllegalStateException: next() returned NONE without first returning
OK_NEW_SCHEMA [#16, ProjectRecordBatch]
> Fragment 0:0
> {noformat}
> If the conversion is applied as UTF8 format,  the same query succeeds: 
> {noformat}
> 0: jdbc:drill:zk=local> select convert_from('{"abc":"xyz"}', 'utf8') as x from cp.`tpch/region.parquet`
where r_regionkey = 9999;
> +----+
> | x  |
> +----+
> +----+
> No rows selected (0.241 seconds)
> {noformat}
> The reason for this is the special handling in the ProjectRecordBatch for JSON.  The
output schema is not known for this until the run time and the ComplexWriter in the Project
relies on seeing the input data to determine the output schema - this could be a MapVector
or ListVector etc.  
> If the input data has 0 rows due to a filter condition, we should at least produce a
default output schema, e.g an empty MapVector ?  Need to decide a good default.  Note that
the CONVERT_FROM(x, 'json') could occur on 2 branches of a UNION-ALL and if one input is empty
while the other side is not, it may still cause incompatibility.



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