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From "Rahul Challapalli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-2743) Parquet file metadata caching
Date Mon, 24 Aug 2015 20:40:45 GMT

    [ https://issues.apache.org/jira/browse/DRILL-2743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14710026#comment-14710026
] 

Rahul Challapalli commented on DRILL-2743:
------------------------------------------

Steven,

I see block locations as part of the cached file. Are these Hdfs/MaprFs block locations? If
so, do we handle the situation when the blocks get shuffled by the balancer?

- Rahul

> Parquet file metadata caching
> -----------------------------
>
>                 Key: DRILL-2743
>                 URL: https://issues.apache.org/jira/browse/DRILL-2743
>             Project: Apache Drill
>          Issue Type: New Feature
>          Components: Storage - Parquet
>            Reporter: Steven Phillips
>            Assignee: Steven Phillips
>             Fix For: 1.2.0
>
>         Attachments: DRILL-2743.patch, drill.parquet_metadata
>
>
> To run a query against parquet files, we have to first recursively search the directory
tree for all of the files, get the block locations for each file, and read the footer from
each file, and this is done during the planning phase. When there are many files, this can
result in a very large delay in running the query, and it does not scale.
> However, there isn't really any need to read the footers during planning, if we instead
treat each parquet file as a single work unit, all we need to know are the block locations
for the file, the number of rows, and the columns. We should store only the information which
we need for planning in a file located in the top directory for a given parquet table, and
then we can delay reading of the footers until execution time, which can be done in parallel.



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