On Mon, Jul 22, 2019 at 7:39 PM Eugene Kirpichov <kirpic...@google.com> wrote:
>
> On Mon, Jul 22, 2019 at 7:49 AM Robert Bradshaw <rober...@google.com> wrote:
>>
>> On Mon, Jul 22, 2019 at 4:04 PM Neville Li <neville....@gmail.com> wrote:
>> >
>> > Thanks Robert. Agree with the FileIO point. I'll look into it and see what
>> > needs to be done.
>> >
>> > Eugene pointed out that we shouldn't build on FileBased{Source,Sink}. So
>> > for writes I'll probably build on top of WriteFiles.
>>
>> Meaning it could be parameterized by FileIO.Sink, right?
>>
>> https://github.com/apache/beam/blob/release-2.13.0/sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileIO.java#L779
>
> Yeah if possible, parameterize FileIO.Sink.
> I would recommend against building on top of WriteFiles either. FileIO being
> implemented on top of WriteFiles was supposed to be a temporary measure - the
> longer-term plan was to rewrite it from scratch (albeit with a similar
> structure) and throw away WriteFiles.
> If possible, I would recommend to pursue this path: if there are parts of
> WriteFiles you want to reuse, I would recommend to implement them as new
> transforms, not at all tied to FileBasedSink (but ok if tied to FileIO.Sink),
> with the goal in mind that FileIO could be rewritten on top of these new
> transforms, or maybe parts of WriteFiles could be swapped out for them
> incrementally.
Thanks for the feedback. There's a lot that was done, but looking at
the code it feels like there's a lot that was not yet done either, and
the longer-term plan wasn't clear (though perhaps I'm just not finding
the right docs).
>> > Read might be a bigger change w.r.t. collocating ordered elements across
>> > files within a bucket and TBH I'm not even sure where to start.
>>
>> Yeah, here we need an interface that gives us ReadableFile ->
>> Iterable<T>. There are existing PTransform<PCollection<ReadableFile>,
>> PCollection<T>> but such an interface is insufficient to extract
>> ordered records per shard. It seems the only concrete implementations
>> are based on FileBasedSource, which we'd like to avoid, but there's no
>> alternative. An SDF, if exposed, would likely be overkill and
>> cumbersome to call (given the reflection machinery involved in
>> invoking DoFns).
>
> Seems easiest to just define a new regular Java interface for this.
> Could be either, indeed, ReadableFile -> Iterable<T>, or something analogous,
> e.g. (ReadableFile, OutputReceiver<T>) -> void. Depends on how much control
> over iteration you need.
For this application, one wants to iterate over several files in
parallel. The downside of a new interface is that it shares almost
nothing with the "normal" sources (e.g. when features (or
optimizations) get added to one, they won't get added to the other).
> And yes, DoFn's including SDF's are not designed to be used as Java
> interfaces per se. If you need DoFn machinery in this interface (e.g. side
> inputs), use Contextful - s.apache.org/context-fn.
Yeah, one of the primary downsides to the NewDoFns is how hard it is
to build new DoFns out of others (or, really, use them in any context
other than as an argument to ParDo).
>> > I'll file separate PRs for core changes needed for discussion. WDYT?
>>
>> Sounds good.
>>
>> > On Mon, Jul 22, 2019 at 4:20 AM Robert Bradshaw <rober...@google.com>
>> > wrote:
>> >>
>> >> On Fri, Jul 19, 2019 at 5:16 PM Neville Li <neville....@gmail.com> wrote:
>> >> >
>> >> > Forking this thread to discuss action items regarding the change. We
>> >> > can keep technical discussion in the original thread.
>> >> >
>> >> > Background: our SMB POC showed promising performance & cost saving
>> >> > improvements and we'd like to adopt it for production soon (by EOY). We
>> >> > want to contribute it to Beam so it's better generalized and
>> >> > maintained. We also want to avoid divergence between our internal
>> >> > version and the PR while it's in progress, specifically any breaking
>> >> > change in the produced SMB data.
>> >>
>> >> All good goals.
>> >>
>> >> > To achieve that I'd like to propose a few action items.
>> >> >
>> >> > 1. Reach a consensus about bucket and shard strategy, key handling,
>> >> > bucket file and metadata format, etc., anything that affect produced
>> >> > SMB data.
>> >> > 2. Revise the existing PR according to #1
>> >> > 3. Reduce duplicate file IO logic by reusing FileIO.Sink, Compression,
>> >> > etc., but keep the existing file level abstraction
>> >> > 4. (Optional) Merge code into extensions::smb but mark clearly as
>> >> > @experimental
>> >> > 5. Incorporate ideas from the discussion, e.g. ShardingFn,
>> >> > GroupByKeyAndSortValues, FileIO generalization, key URN, etc.
>> >> >
>> >> > #1-4 gives us something usable in the short term, while #1 guarantees
>> >> > that production data produced today are usable when #5 lands on master.
>> >> > #4 also gives early adopters a chance to give feedback.
>> >> > Due to the scope of #5, it might take much longer and a couple of big
>> >> > PRs to achieve, which we can keep iterating on.
>> >> >
>> >> > What are your thoughts on this?
>> >>
>> >> I would like to see some resolution on the FileIO abstractions before
>> >> merging into experimental. (We have a FileBasedSink that would mostly
>> >> already work, so it's a matter of coming up with an analogous Source
>> >> interface.) Specifically I would not want to merge a set of per file
>> >> type smb IOs without a path forward to this or the determination that
>> >> it's not possible/desirable.
