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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5207) Improve Parquet scan pipelining
Date Sat, 28 Jan 2017 00:44:25 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15843721#comment-15843721

ASF GitHub Bot commented on DRILL-5207:

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

    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/columnreaders/AsyncPageReader.java
    @@ -74,12 +82,17 @@ protected void loadDictionaryIfExists(final ColumnReader<?>
             handleAndThrowException(e, "Error Reading dictionary page.");
           // parent constructor may call this method before the thread pool is set.
    -      if (threadPool == null) {
    +      if (threadPool == null & asyncPageRead == null) {
             threadPool = parentColumnReader.parentReader.getOperatorContext().getScanExecutor();
    +        queueSize  = parentColumnReader.parentReader.getFragmentContext().getOptions()
    +            .getOption(ExecConstants.PARQUET_PAGEREADER_QUEUE_SIZE).num_val;
    +        if(queueSize < 1) { // A queue with a capacity less than 1 is not cool
    --- End diff --

> Improve Parquet scan pipelining
> -------------------------------
>                 Key: DRILL-5207
>                 URL: https://issues.apache.org/jira/browse/DRILL-5207
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Storage - Parquet
>    Affects Versions: 1.9.0
>            Reporter: Parth Chandra
>            Assignee: Parth Chandra
>             Fix For: 1.10
> The parquet reader's async page reader is not quite efficiently pipelined. 
> The default size of the disk read buffer is 4MB while the page reader reads ~1MB at a
time. The Parquet decode is also processing 1MB at a time. This means the disk is idle while
the data is being processed. Reducing the buffer to 1MB will reduce the time the processing
thread waits for the disk read thread.
> Additionally, since the data to process a page may be more or less than 1MB, a queue
of pages will help so that the disk scan does not block (until the queue is full), waiting
for the processing thread.
> Additionally, the BufferedDirectBufInputStream class reads from disk as soon as it is
initialized. Since this is called at setup time, this increases the setup time for the query
and query execution does not begin until this is completed.
> There are a few other inefficiencies - options are read every time a page reader is created.
Reading options can be expensive.

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