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From "Vihang Karajgaonkar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-17696) Vectorized reader does not seem to be pushing down projection columns in certain code paths
Date Fri, 20 Oct 2017 23:17:02 GMT

    [ https://issues.apache.org/jira/browse/HIVE-17696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16213467#comment-16213467
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Vihang Karajgaonkar commented on HIVE-17696:
--------------------------------------------

+1 Thanks for the patch [~Ferd]

> Vectorized reader does not seem to be pushing down projection columns in certain code
paths
> -------------------------------------------------------------------------------------------
>
>                 Key: HIVE-17696
>                 URL: https://issues.apache.org/jira/browse/HIVE-17696
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: Vihang Karajgaonkar
>            Assignee: Ferdinand Xu
>         Attachments: HIVE-17696.patch
>
>
> This is the code snippet from {{VectorizedParquetRecordReader.java}}
> {noformat}
> MessageType tableSchema;
>     if (indexAccess) {
>       List<Integer> indexSequence = new ArrayList<>();
>       // Generates a sequence list of indexes
>       for(int i = 0; i < columnNamesList.size(); i++) {
>         indexSequence.add(i);
>       }
>       tableSchema = DataWritableReadSupport.getSchemaByIndex(fileSchema, columnNamesList,
>         indexSequence);
>     } else {
>       tableSchema = DataWritableReadSupport.getSchemaByName(fileSchema, columnNamesList,
>         columnTypesList);
>     }
>     indexColumnsWanted = ColumnProjectionUtils.getReadColumnIDs(configuration);
>     if (!ColumnProjectionUtils.isReadAllColumns(configuration) && !indexColumnsWanted.isEmpty())
{
>       requestedSchema =
>         DataWritableReadSupport.getSchemaByIndex(tableSchema, columnNamesList, indexColumnsWanted);
>     } else {
>       requestedSchema = fileSchema;
>     }
>     this.reader = new ParquetFileReader(
>       configuration, footer.getFileMetaData(), file, blocks, requestedSchema.getColumns());
> {noformat}
> Couple of things to notice here:
> Most of this code is duplicated from {{DataWritableReadSupport.init()}} method. 
> the else condition passes in fileSchema instead of using tableSchema like we do in DataWritableReadSupport.init()
method. Does this cause projection columns to be missed when we read parquet files? We should
probably just reuse ReadContext returned from {{DataWritableReadSupport.init()}} method here.



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