beam-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Tobias Feldhaus <Tobias.Feldh...@localsearch.ch>
Subject Re: Implicit file-size limit of input files?
Date Fri, 17 Feb 2017 13:08:50 GMT
Hi Dan,

just one follow up question, as I have completely revised my pipeline now and
want to write AVRO files to GCS first (one per day). You said that 

	by default writing to GCS uses a 64 MiB buffer so if you have 10 partitions 
	you're allocating 640 MiB, per core, just for those network buffers.

Can I somehow optimize this? Would it be possible to partition a PCollection 
into 1000 partitions when using “enough” workers with “enough” memory?

Tobias


On 13.02.17, 09:42, "Tobias Feldhaus" <Tobias.Feldhaus@localsearch.ch> wrote:

    Hi Dan, 
    
    Thank you for your response! 
    
    The approach I am using to write per window tables seems to work in batch and 
    streaming mode, at least this is claimed here [0], and I have confirmed this 
    with the author of this post. I also tested this with smaller files in my own 
    setup. 
    
    Would a shuffling operation on a non-key-value 
    input look like this [1], or is there already some PTransform in the SDK that I 
    am not aware of?
    
    Tobias
    
    [0] http://stackoverflow.com/a/40863609/5497956
    [1] http://stackoverflow.com/a/40769445/5497956
    
    From: Dan Halperin <dhalperi@apache.org>
    Reply-To: "user@beam.apache.org" <user@beam.apache.org>
    Date: Saturday, 11 February 2017 at 21:31
    To: "user@beam.apache.org" <user@beam.apache.org>
    Subject: Re: Implicit file-size limit of input files?
    
    Hi Tobias, 
    
    There should be no specific limitations in Beam on file size or otherwise, obviously different
runners and different size clusters will have different potential scalability.
    
    A few general Beam tips:
    
    * Reading from compressed files is often a bottleneck, as this work is not parallelizable.
If you find reading from compressed files is a bottleneck, you may want to follow it with
a shuffling operation to improve parallelism as most runners can run the work pre- and post-shuffle
on different machines (with different scaling levels).
    
    * The Partition operator on its own does not improve parallelism. Depending on how the
runner arranges the graph, when you partition N ways you may still execute all N partitions
on the same machine. Again, a shuffling operator here will often let runners to execute the
N branches separately.
    
       (There are known issues for certain sinks when N is high. For example, by default writing
to GCS uses a 64 MiB buffer so if you have 10 partitions you're allocating 640 MiB, per core,
just for those network buffers.)
    
    It sounds like you may be trying to use the "to(Partition function)" method of writing
per window tables. The javadoc for BigQueryIO.Write clearly documents (https://github.com/apache/beam/blob/master/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/BigQueryIO.java#L232)
that it is not likely to work in "batch" runners.
    
    I suggest reaching out to Google Cloud via the recommendations at https://cloud.google.com/dataflow/support
if you have issues specific to the Google Cloud Dataflow runner.
    
    Dan
    
    On Fri, Feb 10, 2017 at 3:18 AM, Tobias Feldhaus <Tobias.Feldhaus@localsearch.ch>
wrote:
    Addendum: When running in streaming mode with version 0.5 of the SDK,
    the elements are basically stuck before getting emitted [0], but the whole
    process starts and is running up to a point when most likely the memory is
    full (GC overhead error) and it crashes [0].
    
    It seems like the Reshuffle that is taking place prevents any output to happen.
    To get rid of that, I would need to find another way to write to a partition in
    BigQuery in batch mode without using the workaround that is described here [1],
    but I don't know how.
    
    [0] https://puu.sh/tWInq/f41beae65b.png
    [1] http://stackoverflow.com/questions/38114306/creating-writing-to-parititoned-bigquery-table-via-google-cloud-dataflow/40863609#40863609
    
    On 10.02.17, 10:34, "Tobias Feldhaus" <Tobias.Feldhaus@localsearch.ch> wrote:
    
        Hi,
    
        I am currently facing a problem with a relatively simple pipeline [0] that is
        reading gzipped JSON files on Google Cloud Storage (GCS), adding a timestamp,
        and pushing it into BigQuery. The only special thing I am doing as well is
        partitioning it via a PartioningWindowFn that is assigning a partition
        for each element as described here [1].
    
        The pipeline works locally and remotely on the Google Cloud Dataflow Service
        (GCDS) with smaller test files, but if I run it on the about 100 real ones with
        2GB each it breaks down in streaming and batch mode with different errors.
    
        The pipeline runs in batch mode, but in the end it gets stuck with processing only
        1000-5000 streaming inserts per second to BQ, while constantly scaling up the
        number of instances [2]. As you can see in the screenshot the shuffle never
        started, before I had to stop it to cut the costs.
    
        If run in streaming mode, the pipeline creation fails because of a resource
        allocation failure (Step setup_resource_disks_harness19: Set up of resource
        disks_harness failed: Unable to create data disk(s): One or more operations
        had an error: [QUOTA_EXCEEDED] 'Quota 'DISKS_TOTAL_GB' exceeded.
        Limit: 80000.0) This means, it has requested more than 80 (!) TB for the job that
        operates on 200 GB compressed (or 2 TB uncompressed) files.
    
        I’ve tried to run it with instances that are as large as n1-highmem-16
        (104 GB memory each) and 1200 GB local storage.
    
        I know this is a mailing list of Apache Beam and not intended for GCDF support,
        my question is therefore if anyone has faced the issue with the SDK before, or
        if there is a known size limit for files.
    
    
        Thanks,
        Tobias
    
        [0] https://gist.github.com/james-woods/98901f7ef2b405a7e58760057c48162f
        [1] http://stackoverflow.com/a/40863609/5497956
        [2] https://puu.sh/tWzkh/49b99477e3.png
    
    
    
    
    
    

Mime
View raw message