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https://issues.apache.org/jira/browse/PARQUET-2149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17636711#comment-17636711
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ASF GitHub Bot commented on PARQUET-2149:
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wgtmac commented on PR #968:
URL: https://github.com/apache/parquet-mr/pull/968#issuecomment-1322172984
> > > IMO, switching `ioThreadPool` and `processThreadPool` the reader
instance level will make it more flexible.
> >
> >
> > I've changed the thread pool so that it is not initialized by default
but I left them as static members. Ideally, there should be a single IO thread
pool that handles all the IO for a process and the size of the pool is
determined by the bandwidthof the underlying storage system. Making them per
instance is not an issue though. The calling code can decide to set the same
thread pool for all instances and achieve the same result. Let me update this.
> > Also, any changes you want to make are fine with me, and the help is
certainly appreciated !
>
> I'm thinking of merging the thread pools into a single `ioThreadPool` and
making it settable thru `ParquetReadOptions` (like the allocator is). The work
being done by the `processThreadPool` is rather small and maybe we can do away
with it. Adding the pool via `ParquetReadOptions` makes it easier to use with
`ParquetReader` (used a lot in unit tests). WDYT?
Sorry for my late reply.
Setting the thread pools via `ParquetReadOptions` is a good idea and that is
exactly the way I want to do them away with static members. Merging
`ioThreadPool` and `processThreadPool` into a single pool should work if the
tasks in the `processThreadPool` do not wait for the return of tasks in the
`ioThreadPool`. I will look into the detail later.
BTW, I don't have the permission to directly update your PR in place as I am
not yet a maintainer of the repo. I may need to open a new one by copying what
you have done here and add you as a co-author. WDYT? If that sounds good to
you, I can proceed. @parthchandra
> Implement async IO for Parquet file reader
> ------------------------------------------
>
> Key: PARQUET-2149
> URL: https://issues.apache.org/jira/browse/PARQUET-2149
> Project: Parquet
> Issue Type: Improvement
> Components: parquet-mr
> Reporter: Parth Chandra
> Priority: Major
>
> ParquetFileReader's implementation has the following flow (simplified) -
> - For every column -> Read from storage in 8MB blocks -> Read all
> uncompressed pages into output queue
> - From output queues -> (downstream ) decompression + decoding
> This flow is serialized, which means that downstream threads are blocked
> until the data has been read. Because a large part of the time spent is
> waiting for data from storage, threads are idle and CPU utilization is really
> low.
> There is no reason why this cannot be made asynchronous _and_ parallel. So
> For Column _i_ -> reading one chunk until end, from storage -> intermediate
> output queue -> read one uncompressed page until end -> output queue ->
> (downstream ) decompression + decoding
> Note that this can be made completely self contained in ParquetFileReader and
> downstream implementations like Iceberg and Spark will automatically be able
> to take advantage without code change as long as the ParquetFileReader apis
> are not changed.
> In past work with async io [Drill - async page reader
> |https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/columnreaders/AsyncPageReader.java]
> , I have seen 2x-3x improvement in reading speed for Parquet files.
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