On Wed, May 1, 2019 at 8:51 AM Reuven Lax <re...@google.com> wrote:
> ValueState is not necessarily racy if you're doing a read-modify-write.
> It's only racy if you're doing something like writing last element seen.
>
Race conditions are not inherently a problem. They are neither necessary
nor sufficient for correctness. In this case, it is not the classic sense
of race condition anyhow, it is simply a nondeterministic result, which may
often be perfectly fine.
> On Wed, May 1, 2019 at 8:30 AM Lukasz Cwik <lc...@google.com> wrote:
>>>>
>>>>> Isn't a value state just a bag state with at most one element and the
>>>>> usage pattern would be?
>>>>> 1) value_state.get == bag_state.read.next() (both have to handle the
>>>>> case when neither have been set)
>>>>> 2) user logic on what to do with current state + additional
>>>>> information to produce new state
>>>>> 3) value_state.set == bag_state.clear + bag_state.append? (note that
>>>>> Runners should optimize clear + append to become a single
>>>>> transaction/write)
>>>>>
>>>>
Your unpacking is accurate, but "X is just a Y" is not accurate. In this
case you've demonstrated that value state *can be implemented using* bag
state / has a workaround. But it is not subsumed by bag state. One
important feature of ValueState is that it is statically determined that
the transform cannot be used with merging windows. Another feature is that
it is impossible to accidentally write more than one value. And a third
important feature is that it declares what it is so that the code is more
readable.
Kenn
>
>>>>> For example, the blog post with the counter example would be:
>>>>> @StateId("buffer")
>>>>> private final StateSpec<BagState<Event>> bufferedEvents =
>>>>> StateSpecs.bag();
>>>>>
>>>>> @StateId("count")
>>>>> private final StateSpec<BagState<Integer>> countState =
>>>>> StateSpecs.bag();
>>>>>
>>>>> @ProcessElement
>>>>> public void process(
>>>>> ProcessContext context,
>>>>> @StateId("buffer") BagState<Event> bufferState,
>>>>> @StateId("count") BagState<Integer> countState) {
>>>>>
>>>>> int count = Iterables.getFirst(countState.read(), 0);
>>>>> count = count + 1;
>>>>> countState.clear();
>>>>> countState.append(count);
>>>>> bufferState.add(context.element());
>>>>>
>>>>> if (count > MAX_BUFFER_SIZE) {
>>>>> for (EnrichedEvent enrichedEvent :
>>>>> enrichEvents(bufferState.read())) {
>>>>> context.output(enrichedEvent);
>>>>> }
>>>>> bufferState.clear();
>>>>> countState.clear();
>>>>> }
>>>>> }
>>>>>
>>>>> On Tue, Apr 30, 2019 at 5:39 PM Kenneth Knowles <k...@apache.org>
>>>>> wrote:
>>>>>
>>>>>> Anything where the state evolves serially but arbitrarily - the toy
>>>>>> example is the integer counter in my blog post - needs ValueState. You
>>>>>> can't do it with AnyCombineFn. And I think LatestCombineFn is dangerous,
>>>>>> especially when it comes to CombingState. ValueState is more explicit,
>>>>>> and
>>>>>> I still maintain that it is status quo, modulo unimplemented features in
>>>>>> the Python SDK. The reads and writes are explicitly serial per (key,
>>>>>> window), unlike for a CombiningState. Because of a CombineFn's
>>>>>> requirement
>>>>>> to be associative and commutative, I would interpret it that the runner
>>>>>> is
>>>>>> allowed to reorder inputs even after they are "written" by the user's
>>>>>> DoFn
>>>>>> - for example doing blind writes to an unordered bag, and only later
>>>>>> reading the elements out and combining them in arbitrary order. Or any
>>>>>> other strategy mixing addInput and mergeAccumulators. It would be a
>>>>>> violation of the meaning of CombineFn to overspecify CombiningState
>>>>>> further
>>>>>> than this. So you cannot actually implement a consistent
>>>>>> CombiningState(LatestCombineFn).
>>>>>>
>>>>>> Kenn
>>>>>>
>>>>>> On Tue, Apr 30, 2019 at 5:19 PM Robert Bradshaw <rober...@google.com>
>>>>>> wrote:
>>>>>>
>>>>>>> On Wed, May 1, 2019 at 1:55 AM Brian Hulette <bhule...@google.com>
>>>>>>> wrote:
>>>>>>> >
>>>>>>> > Reza - you're definitely not derailing, that's exactly what I was
>>>>>>> looking for!
>>>>>>> >
>>>>>>> > I've actually recently encountered an additional use case where
>>>>>>> I'd like to use ValueState in the Python SDK. I'm experimenting with an
>>>>>>> ArrowBatchingDoFn that uses state and timers to batch up python
>>>>>>> dictionaries into arrow record batches (actually my entire purpose for
>>>>>>> jumping down this python state rabbit hole).
>>>>>>> >
>>>>>>> > At first blush it seems like the best way to do this would be to
>>>>>>> just replicate the batching approach in the timely processing post [1],
>>>>>>> but
>>>>>>> when the bag is full combine the elements into an arrow record batch,
>>>>>>> rather than enriching all of the elements and writing them out
>>>>>>> separately.
>>>>>>> However, if possible I'd like to pre-allocate buffers for each column
>>>>>>> and
>>>>>>> populate them as elements arrive (at least for columns with a fixed size
>>>>>>> type), so a bag state wouldn't be ideal.
>>>>>>>
>>>>>>> It seems it'd be preferable to do the conversion from a bag of
>>>>>>> elements to a single arrow frame all at once, when emitting, rather
>>>>>>> than repeatedly reading and writing the partial batch to and from
>>>>>>> state with every element that comes in. (Bag state has blind append.)
>>>>>>>
>>>>>>> > Also, a CombiningValueState is not ideal because I'd need to
>>>>>>> implement a merge_accumulators function that combines several
>>>>>>> in-progress
>>>>>>> batches. I could certainly implement that, but I'd prefer that it never
>>>>>>> be
>>>>>>> called unless absolutely necessary, which doesn't seem to be the case
>>>>>>> for
>>>>>>> CombiningValueState. (As an aside, maybe there's some room there for a
>>>>>>> middle ground between ValueState and CombiningValueState
>>>>>>>
>>>>>>> This does actually feel natural (to me), because you're repeatedly
>>>>>>> adding elements to build something up. merge_accumulators would
>>>>>>> probably be pretty easy (concatenation) but unless your windows are
>>>>>>> merging could just throw a not implemented error to really guard
>>>>>>> against it being used.
>>>>>>>
>>>>>>> > I suppose you could argue that this is a pretty low-level
>>>>>>> optimization we should be able to shield our users from, but right now I
>>>>>>> just wish I had ValueState in python so I didn't have to hack it up
>>>>>>> with a
>>>>>>> BagState :)
>>>>>>> >
>>>>>>> > Anyway, in light of this and all the other use-cases mentioned
>>>>>>> here, I think the resolution is to just implement ValueState in python,
>>>>>>> and
>>>>>>> document the danger with ValueState in both Python and Java. Just to be
>>>>>>> clear, the danger I'm referring to is that users might easily forget
>>>>>>> that
>>>>>>> data can be out of order, and use ValueState in a way that assumes it's
>>>>>>> been populated with data from the most recent element in event time,
>>>>>>> then
>>>>>>> in practice out of order data clobbers their state. I'm happy to write
>>>>>>> up a
>>>>>>> PR for this - are there any objections to that?
>>>>>>>
>>>>>>> I still haven't seen a good case for it (though I haven't looked at
>>>>>>> Reza's BiTemporalStream yet). Much harder to remove things once
>>>>>>> they're in. Can we just add a Any and/or LatestCombineFn and use (and
>>>>>>> point to) that instead? With the comment that if you're doing
>>>>>>> read-modify-write, an add_input may be better.
>>>>>>>
>>>>>>> > [1] https://beam.apache.org/blog/2017/08/28/timely-processing.html
>>>>>>> >
>>>>>>> > On Mon, Apr 29, 2019 at 12:23 AM Robert Bradshaw <
>>>>>>> rober...@google.com> wrote:
>>>>>>> >>
>>>>>>> >> On Mon, Apr 29, 2019 at 3:43 AM Reza Rokni <r...@google.com>
>>>>>>> wrote:
>>>>>>> >> >
>>>>>>> >> > @Robert Bradshaw Some examples, mostly built out from cases
>>>>>>> around Timeseries data, don't want to derail this thread so at a hi
>>>>>>> level :
>>>>>>> >>
>>>>>>> >> Thanks. Perfectly on-topic for the thread.
>>>>>>> >>
>>>>>>> >> > Looping timers, a timer which allows for creation of a value
>>>>>>> within a window when no external input has been seen. Requires metadata
>>>>>>> like "is timer set".
>>>>>>> >> >
>>>>>>> >> > BiTemporalStream join, where we need to match leftCol.timestamp
>>>>>>> to a value == (max(rightCol.timestamp) where rightCol.timestamp <=
>>>>>>> leftCol.timestamp)) , this if for a application matching trades to
>>>>>>> quotes.
>>>>>>> >>
>>>>>>> >> I'd be interested in seeing the code here. The fact that you have
>>>>>>> a
>>>>>>> >> max here makes me wonder if combining would be applicable.
>>>>>>> >>
>>>>>>> >> (FWIW, I've long thought it would be useful to do this kind of
>>>>>>> thing
>>>>>>> >> with Windows. Basically, it'd be like session windows with one
>>>>>>> side
>>>>>>> >> being the window from the timestamp forward into the future, and
>>>>>>> the
>>>>>>> >> other side being from the timestamp back a certain amount in the
>>>>>>> past.
>>>>>>> >> This seems a common join pattern.)
>>>>>>> >>
>>>>>>> >> > Metadata is used for
>>>>>>> >> >
>>>>>>> >> > Taking the Key from the KV for use within the OnTimer call.
>>>>>>> >> > Knowing where we are in watermarks for GC of objects in state.
>>>>>>> >> > More timer metadata (min timer ..)
>>>>>>> >> >
>>>>>>> >> > It could be argued that what we are using state for mostly
>>>>>>> workarounds for things that could eventually end up in the API itself.
>>>>>>> For
>>>>>>> example
>>>>>>> >> >
>>>>>>> >> > There is a Jira for OnTimer Context to have Key.
>>>>>>> >> > The GC needs are mostly due to not having a Map State object
>>>>>>> in all runners yet.
>>>>>>> >>
>>>>>>> >> Yeah. GC could probably be done with a max combine. The Key (which
>>>>>>> >> should be in the API) could be an AnyCombine for now (safe to
>>>>>>> >> overwrite because it's always the same).
>>>>>>> >>
>>>>>>> >> > However I think as folks explore Beam there will always be
>>>>>>> little things that require Metadata and so having access to something
>>>>>>> which
>>>>>>> gives us fine grain control ( as Kenneth mentioned) is useful.
>>>>>>> >>
>>>>>>> >> Likely. I guess in line with making easy things easy, I'd like to
>>>>>>> make
>>>>>>> >> dangerous things hard(er). As Kenn says, we'll probably need some
>>>>>>> kind
>>>>>>> >> of lower-level thing, especially if we introduce OnMerge.
>>>>>>> >>
>>>>>>> >> > Cheers
>>>>>>> >> >
>>>>>>> >> > Reza
>>>>>>> >> >
>>>>>>> >> > On Sat, 27 Apr 2019 at 02:59, Kenneth Knowles <k...@apache.org>
>>>>>>> wrote:
>>>>>>> >> >>
>>>>>>> >> >> To be clear, the intent was always that ValueState would be
>>>>>>> not usable in merging pipelines. So no danger of clobbering, but also
>>>>>>> limited functionality. Is there a runner than accepts it and clobbers?
>>>>>>> The
>>>>>>> whole idea of the new DoFn is that it is easy to do the
>>>>>>> construction-time
>>>>>>> analysis and reject the invalid pipeline. It is actually runner
>>>>>>> independent
>>>>>>> and I think already implemented in ParDo's validation, no?
>>>>>>> >> >>
>>>>>>> >> >> Kenn
>>>>>>> >> >>
>>>>>>> >> >> On Fri, Apr 26, 2019 at 10:14 AM Lukasz Cwik <lc...@google.com>
>>>>>>> wrote:
>>>>>>> >> >>>
>>>>>>> >> >>> I am in the camp where we should only support merging state
>>>>>>> (either naturally via things like bags or via combiners). I believe that
>>>>>>> having the wrapper that Brian suggests is useful for users. As for the
>>>>>>> @OnMerge method, I believe combiners should have the ability to look at
>>>>>>> the
>>>>>>> window information and we should treat @OnMerge as syntactic sugar over
>>>>>>> a
>>>>>>> combiner if the combiner API is too cumbersome.
>>>>>>> >> >>>
>>>>>>> >> >>> I believe using combiners can also extend to side inputs and
>>>>>>> help us deal with singleton and map like side inputs when multiple
>>>>>>> firings
>>>>>>> occur. I also like treating everything like a combiner because it will
>>>>>>> give
>>>>>>> us a lot reuse of combiner implementations across all the places they
>>>>>>> could
>>>>>>> be used and will be especially useful when we start exposing APIs
>>>>>>> related
>>>>>>> to retractions on combiners.
>>>>>>> >> >>>
>>>>>>> >> >>> On Fri, Apr 26, 2019 at 9:43 AM Brian Hulette <
>>>>>>> bhule...@google.com> wrote:
>>>>>>> >> >>>>
>>>>>>> >> >>>> Yeah the danger with out of order processing concerns me
>>>>>>> more than the merging as well. As a new Beam user, I immediately
>>>>>>> gravitated
>>>>>>> towards ValueState since it was easy to think about and I just assumed
>>>>>>> there wasn't anything to be concerned about. So it was shocking to learn
>>>>>>> that there is this dangerous edge-case.
>>>>>>> >> >>>>
>>>>>>> >> >>>> What if ValueState were just implemented as a wrapper of
>>>>>>> CombiningState with a LatestCombineFn and documented as such (and
>>>>>>> perhaps
>>>>>>> we encourage users to consider using a CombiningState explicitly if at
>>>>>>> all
>>>>>>> possible)?
>>>>>>> >> >>>>
>>>>>>> >> >>>> Brian
>>>>>>> >> >>>>
>>>>>>> >> >>>>
>>>>>>> >> >>>>
>>>>>>> >> >>>> On Fri, Apr 26, 2019 at 2:29 AM Robert Bradshaw <
>>>>>>> rober...@google.com> wrote:
>>>>>>> >> >>>>>
>>>>>>> >> >>>>> On Fri, Apr 26, 2019 at 6:40 AM Kenneth Knowles <
>>>>>>> k...@apache.org> wrote:
>>>>>>> >> >>>>> >
>>>>>>> >> >>>>> > You could use a CombiningState with a CombineFn that
>>>>>>> returns the minimum for this case.
>>>>>>> >> >>>>>
>>>>>>> >> >>>>> We've also wanted to be able to set data when setting a
>>>>>>> timer that
>>>>>>> >> >>>>> would be returned when the timer fires. (It's in the FnAPI,
>>>>>>> but not
>>>>>>> >> >>>>> the SDKs yet.)
>>>>>>> >> >>>>>
>>>>>>> >> >>>>> The metadata is an interesting usecase, do you have some
>>>>>>> more specific
>>>>>>> >> >>>>> examples? Might boil down to not having a rich enough
>>>>>>> (single) state
>>>>>>> >> >>>>> type.
>>>>>>> >> >>>>>
>>>>>>> >> >>>>> > But I've come to feel there is a mismatch. On the one
>>>>>>> hand, ParDo(<stateful DoFn>) is a way to drop to a lower level and write
>>>>>>> logic that does not fit a more general computational pattern, really
>>>>>>> taking
>>>>>>> fine control. On the other hand, automatically merging state via
>>>>>>> CombiningState or BagState is more of a no-knobs higher level of
>>>>>>> programming. To me there seems to be a bit of a philosophical conflict.
>>>>>>> >> >>>>> >
>>>>>>> >> >>>>> > These days, I feel like an @OnMerge method would be more
>>>>>>> natural. If you are using state and timers, you probably often want more
>>>>>>> direct control over how state from windows gets merged. An of course we
>>>>>>> don't even have a design for timers - you would need some kind of
>>>>>>> timestamp
>>>>>>> CombineFn but I think setting/unsetting timers manually makes more
>>>>>>> sense.
>>>>>>> Especially considering the trickiness around merging windows in the
>>>>>>> absence
>>>>>>> of retractions, you really need this callback, so you can issue
>>>>>>> retractions
>>>>>>> manually for any output your stateful DoFn emitted in windows that no
>>>>>>> longer exist.
>>>>>>> >> >>>>>
>>>>>>> >> >>>>> I agree we'll probably need an @OnMerge. On the other hand,
>>>>>>> I like
>>>>>>> >> >>>>> being able to have good defaults. The high/low level thing
>>>>>>> is a
>>>>>>> >> >>>>> continuum (the indexing example falling towards the high
>>>>>>> end).
>>>>>>> >> >>>>>
>>>>>>> >> >>>>> Actually, the merging questions bother me less than how
>>>>>>> easy it is to
>>>>>>> >> >>>>> accidentally clobber previous values. It looks so easy
>>>>>>> (like the
>>>>>>> >> >>>>> easiest state to use) but is actually the most dangerous.
>>>>>>> If one wants
>>>>>>> >> >>>>> this behavior, I would rather an explicit AnyCombineFn or
>>>>>>> >> >>>>> LatestCombineFn which makes you think about the semantics.
>>>>>>> >> >>>>>
>>>>>>> >> >>>>> - Robert
>>>>>>> >> >>>>>
>>>>>>> >> >>>>> > On Thu, Apr 25, 2019 at 5:49 PM Reza Rokni <
>>>>>>> r...@google.com> wrote:
>>>>>>> >> >>>>> >>
>>>>>>> >> >>>>> >> +1 on the metadata use case.
>>>>>>> >> >>>>> >>
>>>>>>> >> >>>>> >> For performance reasons the Timer API does not support a
>>>>>>> read() operation, which for the vast majority of use cases is not a
>>>>>>> required feature. In the small set of use cases where it is needed, for
>>>>>>> example when you need to set a Timer in EventTime based on the smallest
>>>>>>> timestamp seen in the elements within a DoFn, we can make use of a
>>>>>>> ValueState object to keep track of the value.
>>>>>>> >> >>>>> >>
>>>>>>> >> >>>>> >> On Fri, 26 Apr 2019 at 00:38, Reuven Lax <
>>>>>>> re...@google.com> wrote:
>>>>>>> >> >>>>> >>>
>>>>>>> >> >>>>> >>> I see examples of people using ValueState that I think
>>>>>>> are not captured CombiningState. For example, one common one is users
>>>>>>> who
>>>>>>> set a timer and then record the timestamp of that timer in a
>>>>>>> ValueState. In
>>>>>>> general when you store state that is metadata about other state you
>>>>>>> store,
>>>>>>> then ValueState will usually make more sense than CombiningState.
>>>>>>> >> >>>>> >>>
>>>>>>> >> >>>>> >>> On Thu, Apr 25, 2019 at 9:32 AM Brian Hulette <
>>>>>>> bhule...@google.com> wrote:
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>> Currently the Python SDK does not make ValueState
>>>>>>> available to users. My initial inclination was to go ahead and
>>>>>>> implement it
>>>>>>> there to be consistent with Java, but Robert brings up a great point
>>>>>>> here
>>>>>>> that ValueState has an inherent race condition for out of order data,
>>>>>>> and a
>>>>>>> lot of it's use cases can actually be implemented with a CombiningState
>>>>>>> instead.
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>> It seems to me that at the very least we should
>>>>>>> discourage the use of ValueState by noting the danger in the
>>>>>>> documentation
>>>>>>> and preferring CombiningState in examples, and perhaps we should go
>>>>>>> further
>>>>>>> and deprecate it in Java and not implement it in python. Either way I
>>>>>>> think
>>>>>>> we should be consistent between Java and Python.
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>> I'm curious what people think about this, are there
>>>>>>> use cases that we really need to keep ValueState around for?
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>> Brian
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>> ---------- Forwarded message ---------
>>>>>>> >> >>>>> >>>> From: Robert Bradshaw <rober...@google.com>
>>>>>>> >> >>>>> >>>> Date: Thu, Apr 25, 2019, 08:31
>>>>>>> >> >>>>> >>>> Subject: Re: [docs] Python State & Timers
>>>>>>> >> >>>>> >>>> To: dev <dev@beam.apache.org>
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>> On Thu, Apr 25, 2019, 5:26 PM Maximilian Michels <
>>>>>>> m...@apache.org> wrote:
>>>>>>> >> >>>>> >>>>>
>>>>>>> >> >>>>> >>>>> Completely agree that CombiningState is nicer in this
>>>>>>> example. Users may
>>>>>>> >> >>>>> >>>>> still want to use ValueState when there is nothing to
>>>>>>> combine.
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>> I've always had trouble coming up with any good
>>>>>>> examples of this.
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>>> Also,
>>>>>>> >> >>>>> >>>>> users already know ValueState from the Java SDK.
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>> Maybe we should deprecate that :)
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>>
>>>>>>> >> >>>>> >>>>> On 25.04.19 17:12, Robert Bradshaw wrote:
>>>>>>> >> >>>>> >>>>> > On Thu, Apr 25, 2019 at 4:58 PM Maximilian Michels <
>>>>>>> m...@apache.org> wrote:
>>>>>>> >> >>>>> >>>>> >>
>>>>>>> >> >>>>> >>>>> >> I forgot to give an example, just to clarify for
>>>>>>> others:
>>>>>>> >> >>>>> >>>>> >>
>>>>>>> >> >>>>> >>>>> >>> What was the specific example that was less
>>>>>>> natural?
>>>>>>> >> >>>>> >>>>> >>
>>>>>>> >> >>>>> >>>>> >> Basically every time we use ListState to express
>>>>>>> ValueState, e.g.
>>>>>>> >> >>>>> >>>>> >>
>>>>>>> >> >>>>> >>>>> >> next_index, = list(state.read()) or [0]
>>>>>>> >> >>>>> >>>>> >>
>>>>>>> >> >>>>> >>>>> >> Taken from:
>>>>>>> >> >>>>> >>>>> >>
>>>>>>> https://github.com/apache/beam/pull/8363/files#diff-ba1a2aed98079ccce869cd660ca9d97dR301
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> > Yes, ListState is much less natural here. I think
>>>>>>> generally
>>>>>>> >> >>>>> >>>>> > CombiningValue is often a better replacement. E.g.
>>>>>>> the Java example
>>>>>>> >> >>>>> >>>>> > reads
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> > public void processElement(
>>>>>>> >> >>>>> >>>>> > ProcessContext context, @StateId("index")
>>>>>>> ValueState<Integer> index) {
>>>>>>> >> >>>>> >>>>> > int current = firstNonNull(index.read(), 0);
>>>>>>> >> >>>>> >>>>> > context.output(KV.of(current,
>>>>>>> context.element()));
>>>>>>> >> >>>>> >>>>> > index.write(current+1);
>>>>>>> >> >>>>> >>>>> > }
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> > which is replaced with bag state
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> > def process(self, element,
>>>>>>> state=DoFn.StateParam(INDEX_STATE)):
>>>>>>> >> >>>>> >>>>> > next_index, = list(state.read()) or [0]
>>>>>>> >> >>>>> >>>>> > yield (element, next_index)
>>>>>>> >> >>>>> >>>>> > state.clear()
>>>>>>> >> >>>>> >>>>> > state.add(next_index + 1)
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> > whereas CombiningState would be more natural (than
>>>>>>> ListState, and
>>>>>>> >> >>>>> >>>>> > arguably than even ValueState), giving
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> > def process(self, element,
>>>>>>> index=DoFn.StateParam(INDEX_STATE)):
>>>>>>> >> >>>>> >>>>> > yield element, index.read()
>>>>>>> >> >>>>> >>>>> > index.add(1)
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >
>>>>>>> >> >>>>> >>>>> >>
>>>>>>> >> >>>>> >>>>> >> -Max
>>>>>>> >> >>>>> >>>>> >>
>>>>>>> >> >>>>> >>>>> >> On 25.04.19 16:40, Robert Bradshaw wrote:
>>>>>>> >> >>>>> >>>>> >>> https://github.com/apache/beam/pull/8402
>>>>>>> >> >>>>> >>>>> >>>
>>>>>>> >> >>>>> >>>>> >>> On Thu, Apr 25, 2019 at 4:26 PM Robert Bradshaw <
>>>>>>> rober...@google.com> wrote:
>>>>>>> >> >>>>> >>>>> >>>>
>>>>>>> >> >>>>> >>>>> >>>> Oh, this is for the indexing example.
>>>>>>> >> >>>>> >>>>> >>>>
>>>>>>> >> >>>>> >>>>> >>>> I actually think using CombiningState is more
>>>>>>> cleaner than ValueState.
>>>>>>> >> >>>>> >>>>> >>>>
>>>>>>> >> >>>>> >>>>> >>>>
>>>>>>> https://github.com/apache/beam/blob/release-2.12.0/sdks/python/apache_beam/runners/portability/fn_api_runner_test.py#L262
>>>>>>> >> >>>>> >>>>> >>>>
>>>>>>> >> >>>>> >>>>> >>>> (The fact that one must specify the accumulator
>>>>>>> coder is, however,
>>>>>>> >> >>>>> >>>>> >>>> unfortunate. We should probably infer that if we
>>>>>>> can.)
>>>>>>> >> >>>>> >>>>> >>>>
>>>>>>> >> >>>>> >>>>> >>>> On Thu, Apr 25, 2019 at 4:19 PM Robert Bradshaw <
>>>>>>> rober...@google.com> wrote:
>>>>>>> >> >>>>> >>>>> >>>>>
>>>>>>> >> >>>>> >>>>> >>>>> The desire was to avoid the implicit disallowed
>>>>>>> combination wart in
>>>>>>> >> >>>>> >>>>> >>>>> Python (until we could make sense of it), and
>>>>>>> also ValueState could be
>>>>>>> >> >>>>> >>>>> >>>>> surprising with respect to older values
>>>>>>> overwriting newer ones. What
>>>>>>> >> >>>>> >>>>> >>>>> was the specific example that was less natural?
>>>>>>> >> >>>>> >>>>> >>>>>
>>>>>>> >> >>>>> >>>>> >>>>> On Thu, Apr 25, 2019 at 3:01 PM Maximilian
>>>>>>> Michels <m...@apache.org> wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>> @Pablo: Thanks for following up with the PR! :)
>>>>>>> >> >>>>> >>>>> >>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>> @Brian: I was wondering about this as well. It
>>>>>>> makes the Python state
>>>>>>> >> >>>>> >>>>> >>>>>> code a bit unnatural. I'd suggest to add a
>>>>>>> ValueState wrapper around
>>>>>>> >> >>>>> >>>>> >>>>>> ListState/CombiningState.
>>>>>>> >> >>>>> >>>>> >>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>> @Robert: Like Reuven pointed out, we can
>>>>>>> disallow ValueState for merging
>>>>>>> >> >>>>> >>>>> >>>>>> windows with state.
>>>>>>> >> >>>>> >>>>> >>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>> @Reza: Great. Let's make sure it has Python
>>>>>>> examples out of the box.
>>>>>>> >> >>>>> >>>>> >>>>>> Either Pablo or me could help there.
>>>>>>> >> >>>>> >>>>> >>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>> Thanks,
>>>>>>> >> >>>>> >>>>> >>>>>> Max
>>>>>>> >> >>>>> >>>>> >>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>> On 25.04.19 04:14, Reza Ardeshir Rokni wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>> Pablo, Kenneth and I have a new blog ready
>>>>>>> for publication which covers
>>>>>>> >> >>>>> >>>>> >>>>>>> how to create a "looping timer" it allows for
>>>>>>> default values to be
>>>>>>> >> >>>>> >>>>> >>>>>>> created in a window when no incoming elements
>>>>>>> exists. We just need to
>>>>>>> >> >>>>> >>>>> >>>>>>> clear a few bits before publication, but
>>>>>>> would be great to have that
>>>>>>> >> >>>>> >>>>> >>>>>>> also include a python example, I wrote it in
>>>>>>> java...
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>>> Cheers
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>>> Reza
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>>> On Thu, 25 Apr 2019 at 04:34, Reuven Lax <
>>>>>>> re...@google.com
>>>>>>> >> >>>>> >>>>> >>>>>>> <mailto:re...@google.com>> wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>>> Well state is still not implemented for
>>>>>>> merging windows even for
>>>>>>> >> >>>>> >>>>> >>>>>>> Java (though I believe the idea was to
>>>>>>> disallow ValueState there).
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>>> On Wed, Apr 24, 2019 at 1:11 PM Robert
>>>>>>> Bradshaw <rober...@google.com
>>>>>>> >> >>>>> >>>>> >>>>>>> <mailto:rober...@google.com>> wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>>> It was unclear what the semantics
>>>>>>> were for ValueState for merging
>>>>>>> >> >>>>> >>>>> >>>>>>> windows. (It's also a bit weird as
>>>>>>> it's inherently a race condition
>>>>>>> >> >>>>> >>>>> >>>>>>> wrt element ordering, unlike Bag
>>>>>>> and CombineState, though you can
>>>>>>> >> >>>>> >>>>> >>>>>>> always implement it as a
>>>>>>> CombineState that always returns the latest
>>>>>>> >> >>>>> >>>>> >>>>>>> value which is a bit more explicit
>>>>>>> about the dangers here.)
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> >> >>>>> >>>>> >>>>>>> On Wed, Apr 24, 2019 at 10:08 PM
>>>>>>> Brian Hulette
>>>>>>> >> >>>>> >>>>> >>>>>>> <bhule...@google.com <mailto:
>>>>>>> bhule...@google.com>> wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>> >
>>>>>>> >> >>>>> >>>>> >>>>>>> > That's a great idea! I thought
>>>>>>> about this too after those
>>>>>>> >> >>>>> >>>>> >>>>>>> posts came up on the list recently.
>>>>>>> I started to look into it,
>>>>>>> >> >>>>> >>>>> >>>>>>> but I noticed that there's actually
>>>>>>> no implementation of
>>>>>>> >> >>>>> >>>>> >>>>>>> ValueState in userstate. Is there a
>>>>>>> reason for that? I started
>>>>>>> >> >>>>> >>>>> >>>>>>> to work on a patch to add it but I
>>>>>>> was just curious if there was
>>>>>>> >> >>>>> >>>>> >>>>>>> some reason it was omitted that I
>>>>>>> should be aware of.
>>>>>>> >> >>>>> >>>>> >>>>>>> >
>>>>>>> >> >>>>> >>>>> >>>>>>> > We could certainly replicate the
>>>>>>> example without ValueState
>>>>>>> >> >>>>> >>>>> >>>>>>> by using BagState and clearing it
>>>>>>> before each write, but it
>>>>>>> >> >>>>> >>>>> >>>>>>> would be nice if we could draw a
>>>>>>> direct parallel.
>>>>>>> >> >>>>> >>>>> >>>>>>> >
>>>>>>> >> >>>>> >>>>> >>>>>>> > Brian
>>>>>>> >> >>>>> >>>>> >>>>>>> >
>>>>>>> >> >>>>> >>>>> >>>>>>> > On Fri, Apr 12, 2019 at 7:05 AM
>>>>>>> Maximilian Michels
>>>>>>> >> >>>>> >>>>> >>>>>>> <m...@apache.org <mailto:
>>>>>>> m...@apache.org>> wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>> >>
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > It would probably be pretty
>>>>>>> easy to add the corresponding
>>>>>>> >> >>>>> >>>>> >>>>>>> code snippets to the docs as well.
>>>>>>> >> >>>>> >>>>> >>>>>>> >>
>>>>>>> >> >>>>> >>>>> >>>>>>> >> It's probably a bit more work
>>>>>>> because there is no section
>>>>>>> >> >>>>> >>>>> >>>>>>> dedicated to
>>>>>>> >> >>>>> >>>>> >>>>>>> >> state/timer yet in the
>>>>>>> documentation. Tracked here:
>>>>>>> >> >>>>> >>>>> >>>>>>> >>
>>>>>>> https://jira.apache.org/jira/browse/BEAM-2472
>>>>>>> >> >>>>> >>>>> >>>>>>> >>
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > I've been going over this
>>>>>>> topic a bit. I'll add the
>>>>>>> >> >>>>> >>>>> >>>>>>> snippets next week, if that's fine
>>>>>>> by y'all.
>>>>>>> >> >>>>> >>>>> >>>>>>> >>
>>>>>>> >> >>>>> >>>>> >>>>>>> >> That would be great. The blog
>>>>>>> posts are a great way to get
>>>>>>> >> >>>>> >>>>> >>>>>>> started with
>>>>>>> >> >>>>> >>>>> >>>>>>> >> state/timers.
>>>>>>> >> >>>>> >>>>> >>>>>>> >>
>>>>>>> >> >>>>> >>>>> >>>>>>> >> Thanks,
>>>>>>> >> >>>>> >>>>> >>>>>>> >> Max
>>>>>>> >> >>>>> >>>>> >>>>>>> >>
>>>>>>> >> >>>>> >>>>> >>>>>>> >> On 11.04.19 20:21, Pablo
>>>>>>> Estrada wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > I've been going over this
>>>>>>> topic a bit. I'll add the
>>>>>>> >> >>>>> >>>>> >>>>>>> snippets next week,
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > if that's fine by y'all.
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > Best
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > -P.
>>>>>>> >> >>>>> >>>>> >>>>>>> >> >
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > On Thu, Apr 11, 2019 at 5:27
>>>>>>> AM Robert Bradshaw
>>>>>>> >> >>>>> >>>>> >>>>>>> <rober...@google.com <mailto:
>>>>>>> rober...@google.com>
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > <mailto:rober...@google.com
>>>>>>> <mailto:rober...@google.com>>>
>>>>>>> >> >>>>> >>>>> >>>>>>> wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>> >> >
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > That's a great idea! It
>>>>>>> would probably be pretty easy
>>>>>>> >> >>>>> >>>>> >>>>>>> to add the
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > corresponding code
>>>>>>> snippets to the docs as well.
>>>>>>> >> >>>>> >>>>> >>>>>>> >> >
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > On Thu, Apr 11, 2019 at
>>>>>>> 2:00 PM Maximilian Michels
>>>>>>> >> >>>>> >>>>> >>>>>>> <m...@apache.org <mailto:
>>>>>>> m...@apache.org>
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > <mailto:m...@apache.org
>>>>>>> <mailto:m...@apache.org>>> wrote:
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > >
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > > Hi everyone,
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > >
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > > The Python SDK still
>>>>>>> lacks documentation on state
>>>>>>> >> >>>>> >>>>> >>>>>>> and timers.
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > >
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > > As a first step, what
>>>>>>> do you think about updating
>>>>>>> >> >>>>> >>>>> >>>>>>> these two blog
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > posts
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > > with the corresponding
>>>>>>> Python code?
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > >
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > >
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> https://beam.apache.org/blog/2017/02/13/stateful-processing.html
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > >
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> https://beam.apache.org/blog/2017/08/28/timely-processing.html
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > >
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > > Thanks,
>>>>>>> >> >>>>> >>>>> >>>>>>> >> > > Max
>>>>>>> >> >>>>> >>>>> >>>>>>> >> >
>>>>>>> >> >>>>> >>>>> >>>>>>>
>>>>>>> >> >>>>> >>
>>>>>>> >> >>>>> >>
>>>>>>> >> >>>>> >>
>>>>>>> >> >>>>> >> --
>>>>>>> >> >>>>> >>
>>>>>>> >> >>>>> >> This email may be confidential and privileged. If you
>>>>>>> received this communication by mistake, please don't forward it to
>>>>>>> anyone
>>>>>>> else, please erase all copies and attachments, and please let me know
>>>>>>> that
>>>>>>> it has gone to the wrong person.
>>>>>>> >> >>>>> >>
>>>>>>> >> >>>>> >> The above terms reflect a potential business
>>>>>>> arrangement, are provided solely as a basis for further discussion, and
>>>>>>> are
>>>>>>> not intended to be and do not constitute a legally binding obligation.
>>>>>>> No
>>>>>>> legally binding obligations will be created, implied, or inferred until
>>>>>>> an
>>>>>>> agreement in final form is executed in writing by all parties involved.
>>>>>>> >> >
>>>>>>> >> >
>>>>>>> >> >
>>>>>>> >> > --
>>>>>>> >> >
>>>>>>> >> > This email may be confidential and privileged. If you received
>>>>>>> this communication by mistake, please don't forward it to anyone else,
>>>>>>> please erase all copies and attachments, and please let me know that it
>>>>>>> has
>>>>>>> gone to the wrong person.
>>>>>>> >> >
>>>>>>> >> > The above terms reflect a potential business arrangement, are
>>>>>>> provided solely as a basis for further discussion, and are not intended
>>>>>>> to
>>>>>>> be and do not constitute a legally binding obligation. No legally
>>>>>>> binding
>>>>>>> obligations will be created, implied, or inferred until an agreement in
>>>>>>> final form is executed in writing by all parties involved.
>>>>>>>
>>>>>>
