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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4287) Do lazy reading of parquet metadata cache file
Date Wed, 10 Feb 2016 20:22:18 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15141583#comment-15141583
] 

ASF GitHub Bot commented on DRILL-4287:
---------------------------------------

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

    https://github.com/apache/drill/pull/345#discussion_r52519003
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/ParquetGroupScan.java
---
    @@ -521,6 +543,25 @@ public void setEndpointByteMap(EndpointByteMap byteMap) {
         }
       }
     
    +  private FileSelection
    +  getSelectionFromMetadataCache(DrillFileSystem fs, FileSelection selection) throws IOException
{
    +    FileStatus metaRootDir = selection.getFirstPath(fs);
    +    Path metaFilePath = new Path(metaRootDir.getPath(), Metadata.METADATA_FILENAME);
    +
    +    // get the metadata for the directory by reading the metadata file
    +    Metadata.ParquetTableMetadataBase metadata  = Metadata.readBlockMeta(fs, metaFilePath.toString());
    +    List<String> fileNames = Lists.newArrayList();
    +    for (Metadata.ParquetFileMetadata file : metadata.getFiles()) {
    +      fileNames.add(file.getPath());
    +    }
    +    // when creating the file selection, set the selection root in the form /a/b instead
of
    +    // file:/a/b.  The reason is that the file names above have been created in the form
    +    // /a/b/c.parquet and the format of the selection root must match that of the file
names
    +    // otherwise downstream operations such as partition pruning can break.
    +    final Path metaRootPath = Path.getPathWithoutSchemeAndAuthority(metaRootDir.getPath());
    +    return FileSelection.create(selection.getStatuses(fs), fileNames, metaRootPath.toString());
    --- End diff --
    
    `FileSelection.create()` expects either a list of statuses or a list of filenames, but
not both.


> Do lazy reading of parquet metadata cache file
> ----------------------------------------------
>
>                 Key: DRILL-4287
>                 URL: https://issues.apache.org/jira/browse/DRILL-4287
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Query Planning & Optimization
>    Affects Versions: 1.4.0
>            Reporter: Aman Sinha
>            Assignee: Jinfeng Ni
>
> Currently, the parquet metadata cache file is read eagerly during creation of the DrillTable
(as part of ParquetFormatMatcher.isReadable()).  This is not desirable from performance standpoint
since there are scenarios where we want to do some up-front optimizations - e.g. directory-based
partition pruning (see DRILL-2517) or potential limit 0 optimization etc. - and in such situations
it is better to do lazy reading of the metadata cache file.   
> This is a placeholder to perform such delayed reading since it is needed for the aforementioned
optimizations.  



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