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From Cheng Su <>
Subject Re: [DISCUSS] Time to evaluate "continuous mode" in SS?
Date Thu, 17 Sep 2020 00:47:29 GMT
I am +1 to take a look and participate in continuous shuffle work, while push-based shuffle
is being added. To be honest, I feel it might be hard to get people’s hard commitment on
this, as it depends on progress of another SPIP, and timeline for discussion/work can be several
months later.

Cheng Su

From: Jungtaek Lim <>
Date: Tuesday, September 15, 2020 at 5:04 PM
To: Joseph Torres <>
Cc: Sean Owen <>, dev <>
Subject: Re: [DISCUSS] Time to evaluate "continuous mode" in SS?

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

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 <<>>
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 <<>>
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
<<>> 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 <<>>
>> 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
>> <<>> 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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