Hello again,
I created tickets to capture these requests:
https://issues.apache.org/jira/browse/BEAM-2750
https://issues.apache.org/jira/browse/BEAM-2751
I've started working on the Write part.
Robert, after some time working on this, I'm unable to see how these
objectives can be "entirely done in the context of a DoFn". Could you lend
a hint?
I assume you didn't mean for me to append to my pipeline a ParDo.of(new
DoFn... that manually writes out to some file location, did you? That would
lose all the benefits of the IO/Sink classes.
That said, I've found the "sharding" logic to be deeply embedded in all the
FileBaseSink derivatives, and my attempt at sidestepping this logic isn't
going very well. I managed to write a FileBasedSink that writes Byte[] out
(and that works correctly), but figuring out how to get the FIlenamePolicy
to be different for each element written out seems counter to the intent of
much of these classes.
Chris
On Wed, Aug 2, 2017 at 10:23 AM, Reuven Lax <re...@google.com.invalid>
wrote:
> On Wed, Aug 2, 2017 at 7:49 AM, Chris Hebert <
> chris.hebert-...@digitalreasoning.com> wrote:
>
> > Thanks for the feedback!
> >
> > Aggregated thoughts:
> >
> > 1. Warn users about large files (like 5GB large)
> >
>
> I would set the threshold smaller. Also remember, that while you may warn,
> some runners might simply fail to process the record causing pipelines to
> either get stuck or fail all together.
>
>
> > 2. Filenames can stick with contents via PCollection<KV<filename,
> > contents>>
> > 3. InputStreams can't be encoded directly, but could be referenced in
> a
> > FileWrapper object
> > 4. Be mindful of sink race conditions with multiple workers; make sure
> > failed workers cleanup incompletely written files
> > 5. File systems often do better with few large files than many small
> > ones
> > 6. Most/all of this can be done in the context of a DoFn
> >
> > # Regarding point 1 and point 2
> > Yes!
> >
> > # Regarding point 3:
> >
> > ## Approach A:
> > When the FileWrapper is encoded, it must somehow encode a reference to
> the
> > InputStream it is associated with, so that when the FileWrapper is
> decoded
> > it can pick up that InputStream again. My Java knowledge isn't deep
> enough
> > to know how one would do that with hashcodes and object lookup and such,
> > but I could sidestep that entirely by simply encoding the filepath with
> the
> > FileWrapper, then open up a new InputStream on that file path every time
> > the FileWrapper is decoded.
> >
> > ## Approach B:
> > An alternative to the above technique is to simply pass a byte[] array,
> > like so:
> > PCollection<KV<String, byte[]>> fileNamesAndBytes = p.apply("Read",
> > WholeFileIO.read().from("/path/to/input/dir/*"));
> >
> > That would solve the encoding problem, allow users to get whatever they
> > want out of it with a ByteArrayInputStream, AND put a hard limit on the
> > size of incoming files at just below 2 GB (if my math is right). (This is
> > large enough for my use case, at present.)
> >
> >
> > # Regarding point 4:
> >
> > Any examples or guidance I could pull from to protect against this
> > properly?
> >
> >
> > # Regarding point 5:
> >
> > TextIO can read and write with different compressions. Would it be
> feasible
> > for this WholeFileIO to read and write these many files to compressed zip
> > files also? (I envision this as a stretch feature that would be added
> after
> > the initial iteration anyway.)
> >
> >
> > # Regarding point 6:
> >
> > The only prebuilt IO thing I've found find in Beam that uses DoFn is
> > WriteFiles. Do you have any examples to point towards to enlighten me on
> > the use of DoFn in this context? Unfortunately, we all know the
> "Authoring
> > I/O Transforms" documentation is sparse.
> >
> >
> > Keep it coming,
> > Chris
> >
> > On Tue, Aug 1, 2017 at 3:55 PM, Robert Bradshaw
> > <rober...@google.com.invalid
> > > wrote:
> >
> > > On Tue, Aug 1, 2017 at 1:42 PM, Eugene Kirpichov <
> > > kirpic...@google.com.invalid> wrote:
> > >
> > > > Hi,
> > > > As mentioned on the PR - I support the creation of such an IO (both
> > read
> > > > and write) with the caveats that Reuven mentioned; we can refine the
> > > naming
> > > > during code review.
> > > > Note that you won't be able to create a PCollection<InputStream>
> > because
> > > > elements of a PCollection must have a coder and it's not possible to
> > > > provide a coder for InputStream.
> > >
> > >
> > > Well, it's possible, but the fact that InputStream is mutable may cause
> > > issues (e.g. if there's fusion, or when estimating its size).
> > >
> > > I would probably let the API consume/produce a PCollection<KV<filename,
> > > contents>>. Alternatively, a FileWrapper object of some kind could
> > provide
> > > accessors to InputStream (or otherwise facilitate lazy reading).
> > >
> > > Note for the sink one must take care there's no race in case multiple
> > > workers are attempting to process the same bundle (and ideally cleanup
> in
> > > the face of failure). Other than that, these could be entirely done in
> > the
> > > context of a DoFn.
> > >
> > > Also not that most filesystems, especially distributed ones, do better
> > > reading and writing fewer larger files than many, many small ones.
> > >
> > >
> > > > On Tue, Aug 1, 2017 at 1:33 PM Reuven Lax <re...@google.com.invalid>
> > > > wrote:
> > > >
> > > > > One thing to keep in mind is that many runners might have issues
> with
> > > > huge
> > > > > elements. If you have a 5gb file, encoding it as a single element
> > might
> > > > > give you pain or might simply not work on some runners.
> > > > >
> > > > > Reuven
> > > > >
> > > > > On Tue, Aug 1, 2017 at 1:22 PM, Chris Hebert <
> > > > > chris.hebert-...@digitalreasoning.com> wrote:
> > > > >
> > > > > > Hi,
> > > > > >
> > > > > > I'd like to:
> > > > > >
> > > > > > 1. Read whole files as one input each. (If my input files are
> > > > hi.txt,
> > > > > > what.txt, and yes.txt, then the whole contents of hi.txt are
> an
> > > > > element
> > > > > > of
> > > > > > the returned PCollection, the whole contents of what.txt are
> the
> > > > next
> > > > > > element, etc.)
> > > > > > 2. Write elements as individual files. (Rather than smashing
> > > > thousands
> > > > > > of outputs into a handful of files as TextIO does:
> > > > > > output-00000-of-00005,
> > > > > > output-00001-of-00005,..., I want to output each thing
> > > individually.
> > > > > So
> > > > > > if
> > > > > > I'm given hi.txt, what.txt, yes.txt then I'd like to read
> those
> > in
> > > > as
> > > > > > whole
> > > > > > files individually, then write out my processed results as
> > > > > > hi.txt-modified,
> > > > > > what.txt-modified, yes.txt-modified.).
> > > > > >
> > > > > > Before reading on, if you have easier ways to do these things,
> then
> > > I'd
> > > > > > love to hear them!
> > > > > >
> > > > > > # Part 1
> > > > > >
> > > > > > I attempted Part 1 with this PR:
> > > > > > https://github.com/apache/beam/pull/3543
> > > > > >
> > > > > > But I overgeneralized.
> > > > > >
> > > > > > Specifically, I want:
> > > > > >
> > > > > > Pipeline p = Pipeline.create(options);
> > > > > > PCollection<Strings> wholeFilesAsStrings = p.apply("Read Whole
> > Files
> > > > from
> > > > > > Input Directory", WholeFileIO.read().from("/
> > path/to/input/dir/*"));
> > > > > >
> > > > > > or
> > > > > >
> > > > > > Pipeline p = Pipeline.create(options);
> > > > > > PCollection<InputStream> wholeFileStreams = p.apply("Read Whole
> > Files
> > > > > from
> > > > > > Input Directory", WholeFileIO.read().from("/
> > path/to/input/dir/*"));
> > > > > >
> > > > > > Bonus points would include:
> > > > > >
> > > > > > - Keeping the filename somehow
> > > > > >
> > > > > >
> > > > > > # Part 2
> > > > > >
> > > > > > Currently, if you output hundreds of thousands of elements
> > > (batch-mode)
> > > > > > with TextIO in Beam on Flink with, say, 45 TaskManagers, then you
> > get
> > > > > > output-00000-of-00045, output-00001-of-00045, etc., and each one
> of
> > > > those
> > > > > > files contain tens of thousands of outputs back to back. I want
> > them
> > > to
> > > > > be
> > > > > > output as individual files.
> > > > > >
> > > > > > If appended after code snippets from Part 1, it would look like:
> > > > > >
> > > > > > ...
> > > > > > p.apply("Write Whole File Outputs",
> > > > > > WholeFileIO.write().to("/path/to/output/dir/"));
> > > > > >
> > > > > > Bonus points would include:
> > > > > >
> > > > > > - Writing each element of the given PCollection to the
> filename
> > > > they'd
> > > > > > like to go to.
> > > > > > - Parallelizable. (This might already be done, I just noticed
> > that
> > > > my
> > > > > > Beam+Flink+YARN pipeline with TextIO.write() only had one
> > > > TaskManager
> > > > > > writing the DataSink output even though all other components
> of
> > my
> > > > > > pipeline
> > > > > > had many TaskManagers working on them simultaneously. I
> haven't
> > > > found
> > > > > > the
> > > > > > way to fix that yet. The current arrangement added 15 minutes
> to
> > > the
> > > > > > end of
> > > > > > my pipeline as the lonely TaskManager did all the output.)
> > > > > >
> > > > > >
> > > > > > I'm available to put the dev work into this. (Actually, I'm
> putting
> > > dev
> > > > > > time into some kind of solution whether this is agreed upon or
> not
> > > :).
> > > > > >
> > > > > > Feedback, please,
> > > > > > Chris
> > > > > >
> > > > >
> > > >
> > >
> >
>
