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From Jungtaek Lim <kabhwan.opensou...@gmail.com>
Subject Re: [DISCUSS] Time to evaluate "continuous mode" in SS?
Date Wed, 16 Sep 2020 00:03:56 GMT
Yeah I realized there's a proposal for push-based shuffle, and I agree that
may unblock the architectural issue on true-streaming. (The root concern of
the continuous mode has been that it doesn't fit with the architecture of
Spark, and probably push-based shuffle could persuade me.)

I guess push-based shuffle is not the only blocker to make continuous mode
be stateful (all of the assumptions on microbatch are broken in the mode,
like global watermark, distributed checkpoint without stopping every tasks,
etc.), but even just repartitioning (probably easier to achieve) is still a
good improvement for the continuous mode. If someone is promising to look
into the improvement after the push-based shuffle, I agree that is a good
reason to keep continuous mode in place.

On Tue, Sep 15, 2020 at 11:02 PM Joseph Torres <joseph.torres@databricks.com>
wrote:

> It's worth noting that the push-based shuffle SPIP currently in progress
> addresses a substantial blocker in the area. If you remember when we
> removed the half-finished stateful query support, the lack of that
> functionality and the challenge of implementing it is basically why it was
> half-finished. I can't make a hard commitment, but I do plan to take a look
> at how easy it would be to build continuous shuffle support on top of the
> SPIP once it's in, and continuous mode is gonna be a lot more useful if
> most (all?) queries can run using it.
>
> On Tue, Sep 15, 2020 at 6:37 AM Sean Owen <srowen@gmail.com> wrote:
>
>> I think we certainly can't remove it without deprecation and a few
>> releases. If there were big problems with it that weren't getting
>> fixed, sure maybe, but lack of interest in reviewing minor changes
>> isn't necessarily a bad sign. By the same logic you'd delete graphx
>> long ago.
>>
>> Anecdotally, yes there are people using it that I know of at least,
>> but I wouldn't know a lot of them.
>> I think the question is, is it causing a problem, like a lot of
>> maintenance? doesn't sound like it.
>>
>> On Tue, Sep 15, 2020 at 8:19 AM Jungtaek Lim
>> <kabhwan.opensource@gmail.com> wrote:
>> >
>> > Probably it would depend on the meaning of "experimental". My
>> understanding of "experimental" is more likely "incubation", which may be
>> graduated finally, or may be retired.
>> >
>> > To be clear, I'm evaluating the continuous mode as "candidate to
>> retire", unless there are actual use cases in production and at least a
>> couple of community members volunteer to maintain it. As far as I see the
>> activity in a year, there's no interest for the continuous mode in
>> community members. I can refer to at least three PRs which suffered to find
>> reviewers (around 1 year) and closed on inactivity. No improvements/bug
>> fixes except trivials. It doesn't seem to get some traction - few questions
>> in SO, a few posts in google search results which were all posted around
>> the date when continuous mode was introduced. Though I would be convinced
>> if someone could provide meaningful numbers of actual use cases.
>> >
>> > If the answer really has to be taken between un-experimental or not
>> (which says retirement is not an option), I'd rather vote to leave as
>> experimental, so I just keep forgetting about it. Actually it bothers
>> sometimes even if the change is done in micro-batch side (so that's not a
>> zero cost to maintain), but still better than officially supporting it.
>> >
>> >
>> > On Tue, Sep 15, 2020 at 9:08 PM Sean Owen <srowen@gmail.com> wrote:
>> >>
>> >> If you're suggesting making it un-Experimental, probably yes, as it is
>> >> de facto not going to change much I expect.
>> >> If you're saying remove it, probably not? I don't see that it's
>> >> anywhere near deprecated, and not sure it's unmaintained - obviously
>> >> tests etc still have to keep passing.
>> >>
>> >> On Mon, Sep 14, 2020 at 11:34 PM Jungtaek Lim
>> >> <kabhwan.opensource@gmail.com> wrote:
>> >> >
>> >> > Hi devs,
>> >> >
>> >> > It was Spark 2.3 in Feb 2018 which introduced continuous mode in
>> Structured Streaming as "experimental".
>> >> >
>> >> > Now we are here at 2.5 years after its release - I feel it would be
>> a good time to evaluate the mode, whether the mode has been widely used or
>> not, and the mode has been making progress, as the mode is "experimental".
>> >> >
>> >> > At least from the surface I don't see any active effort for
>> continuous mode around the community - the last major effort was stateful
>> operation which was incomplete and I removed that. There were some couples
>> of bug reports as well as fixes more than a year ago and almost nothing has
>> been handled. (A trivial bugfix PR has been merged recently but that's
>> all.) The new features introduced to the Structured Streaming (at least
>> observable metrics, SS UI) don't apply to continuous mode, and no one made
>> "support continuous mode" as a hard requirement on passing review in these
>> PRs.
>> >> >
>> >> > I have no idea how many companies are using the mode in production
>> (please add the voice if someone has statistics about this) but I don't see
>> any bug reports recently, and see only a few questions in SO, which makes
>> me think about cost on maintenance.
>> >> >
>> >> > I know there's a mood to avoid discontinue support as possible, but
>> it sounds weird to keep something as "unmaintained", especially it's still
>> "experimental" and main authors are no more active enough to promise
>> maintenance/improvement on the module. Thoughts?
>> >> >
>> >> > Thanks,
>> >> > Jungtaek Lim (HeartSaVioR)
>>
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