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From peay <p...@protonmail.com>
Subject Re: Using watermarks with bounded sources
Date Wed, 21 Jun 2017 21:18:09 GMT
Thanks, great news! Are there plans to get ProcessContinuation from the original proposal into
the API?

-------- Original Message --------
Subject: Re: Using watermarks with bounded sources
Local Time: June 20, 2017 7:52 PM
UTC Time: June 20, 2017 11:52 PM
From: kirpichov@google.com
To: peay <peay@protonmail.com>, klk@google.com <klk@google.com>
user@beam.apache.org <user@beam.apache.org>

Hi!

The PR just got submitted. You can play with SDF in Dataflow streaming runner now :) Hope
it doesn't get rolled back (fingers crossed)...

On Mon, Jun 19, 2017 at 6:06 PM Eugene Kirpichov <kirpichov@google.com> wrote:

Hi,
The PR is ready and I'm just struggling with setup of tests - Dataflow ValidatesRunner tests
currently don't have a streaming execution.
I think [+Kenn Knowles](mailto:klk@google.com) was doing something about that, or I might
find a workaround.

But basically if you want to experiment - if you patch in the PR, you can experiment with
SDF in Dataflow in streaming mode. It passes tests against the current production Dataflow
Service.

On Thu, Jun 15, 2017 at 8:54 AM peay <peay@protonmail.com> wrote:
Eugene, would you have an ETA on when splittable DoFn would be available in Dataflow in batch/streaming
mode? I see that https://github.com/apache/beam/pull/1898 is still active

I've started to experiment with those using the DirectRunner and this is a great API.

Thanks!

-------- Original Message --------
Subject: Re: Using watermarks with bounded sources
Local Time: April 23, 2017 10:18 AM
UTC Time: April 23, 2017 2:18 PM
From: peay@protonmail.com
To: Eugene Kirpichov <kirpichov@google.com>
user@beam.apache.org <user@beam.apache.org>

Ah, I didn't know about that. This is *really* great -- from a quick look, the API looks both
very natural and very powerful. Thanks a lot for getting this into Beam!

I see Flink support seems to have been merged already. Any idea on when https://github.com/apache/beam/pull/1898
will get merged?

I see updateWatermark in the API but not in the proposal's examples which only uses resume/withFutureOutputWatermark.
Any reason why updateWatermark is not called after each output in the examples from the proposal?
I guess that would be "too fined-grained" to update it for each individual record of a mini-batch?

In my case with existing hourly files, would `outputElement(01:00 file), updateWatermark(01:00),
outputElement(02:00), updateWatermark(02:00), ...` be the proper way to output per-hour elements
while gradually moving the watermark forward while going through an existing list? Or would
you instead suggest to still use resume (potentially with were small timeouts)?

Thanks,

-------- Original Message --------
Subject: Re: Using watermarks with bounded sources
Local Time: 22 April 2017 3:59 PM
UTC Time: 22 April 2017 19:59
From: kirpichov@google.com
To: peay <peay@protonmail.com>, user@beam.apache.org <user@beam.apache.org>

Hi! This is an excellent question; don't have time to reply in much detail right now, but
please take a look at http://s.apache.org/splittable-do-fn - it unifies the concepts of bounded
and unbounded sources, and the use case you mentioned is one of the motivating examples.

Also, see recent discussions on pipeline termination semantics: technically nothing should
prevent an unbounded source from saying it's done "for real" (no new data will appear), just
the current UnboundedSource API does not expose such a method. (but Splittable DoFn does)

On Sat, Apr 22, 2017 at 11:15 AM peay <peay@protonmail.com> wrote:
Hello,

A use case I find myself running into frequently is the following: I have daily or hourly
files, and a Beam pipeline with a small to moderate size windows. (Actually, I've just seen
that support for per-window files support in file based sinks was recently checked in, which
is one way to get there).

Now, Beam has no clue about the fact that each file corresponds to a given time interval.
My understanding is that when running the pipeline in batch mode with a bounded source, there
is no notion watermark and we have to load everything because we just don't know. This is
pretty wasteful, especially as you have to keep a lot of data in memory, while you could in
principle operate close to what you'd do in streaming mode: first read the oldest files, then
newest files, moving the watermark forward as you go through the input list of files.

I see one way around this. Let's say that I have hourly files and let's not assume anything
about the order of records within the file to keep it simple: I don't want a very precise
record-level watermark, but more a rough watermark at the granularity of hours. Say we can
easily get the corresponding time interval from the filename. One can make an unbounded source
that essentially acts as a "List of bounded file-based sources". If there are K splits, split
k can read every file that has `index % K == k` in the time-ordered list of files. `advance`
can advance the current file, and move on to the next one if no records were read.

However, as far as I understand, this pipeline will never terminate since this is an unbounded
source and having the `advance` method of our wrapping source return `false` won't make the
pipeline terminate. Can someone confirm if this is correct? If yes, what would be ways to
work around that? There's always the option to throw to make the pipeline fail, but this is
far from ideal.

Thanks,
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