Hi Jorge,
Sorry for my silence, I've been absorbed with the 2.6 and 2.5.1 releases.
The idea to separate the new methods into "mixin" interfaces seems
like a good one, but as we've discovered in KIP-614, it doesn't work
out that way in practice. The problem is that the store implementations
are just the base layer that get composed with other layers in Streams
before they can be accessed in the DSL. This is extremely subtle, so
I'm going to put everyone to sleep with a detailed explanation:
For example, this is the mechanism by which all KeyValueStore
implementations get added to Streams:
org.apache.kafka.streams.state.internals.KeyValueStoreBuilder#build
return new MeteredKeyValueStore<>(
maybeWrapCaching(maybeWrapLogging(storeSupplier.get())),
storeSupplier.metricsScope(),
time,
keySerde,
valueSerde
);
In the DSL, the store that a processor gets from the context would be
the result of this composition. So even if the storeSupplier.get() returns
a store that implements the "reverse" interface, when you try to use it
from a processor like:
org.apache.kafka.streams.kstream.ValueTransformerWithKey#init
ReadOnlyBackwardWindowStore<K, V> store =
(ReadOnlyBackwardWindowStore<K, V>) context.getStateStore(..)
You'd just get a ClassCastException because it's actually a
MeteredKeyValueStore, which doesn't implement
ReadOnlyBackwardWindowStore.
The only way to make this work would be to make the Metered,
Caching, and Logging layers also implement the new interfaces,
but this effectively forces implementations to also implement
the interface. Otherwise, the intermediate layers would have to
cast the store in each method, like this:
MeteredWindowStore#backwardFetch {
((ReadOnlyBackwardWindowStore<K, V>) innerStore).backwardFetch(..)
}
And then if the implementation doesn't "opt in" by implementing
the interface, you'd get a ClassCastException, not when you get the
store, but when you try to use it.
The fact that we get ClassCastExceptions no matter which way we
turn here indicates that we're really not getting any benefit from the
type system, which makes the extra interfaces seem not worth all the
code involved.
Where we landed in KIP-614 is that, unless we want to completely
revamp the way that StateStores work in the DSL, you might as
well just add the new methods to the existing interfaces. To prevent
compilation errors, we can add default implementations that throw
UnsupportedOperationException. If a store doesn't opt in by
implementing the methods, you'd get an UnsupportedOperationException,
which seems no worse, and maybe better, than the ClassCastException
you'd get if we go with the "mixin interface" approach.
A quick note: This entire discussion focuses on the DSL. If you're just
using the Processor API by directly adding the a custom store to the
Topology:
org.apache.kafka.streams.Topology#addStateStore
and then retrieving it in the processor via:
org.apache.kafka.streams.processor.ProcessorContext#getStateStore
in
org.apache.kafka.streams.processor.Processor#init
Then, you can both register and retrieve _any_ StateStore implementation.
There's no need to use KeyValueStore or any other built-in interface.
In other words, KeyValueStore and company are only part of the DSL,
not the PAPI. So, discussions about the build-in store interfaces are only
really relevant in the context of the DSL, Transformers, and Materialized.
So, in conclusion, I'd really recommend just adding any new methods to
the existing store interfaces. We might be able to revamp the API in the
future to support mixins, but it's a much larger scope of work than this KIP.
A more minor comment is that we don't need to add Deprecated variants
of new methods.
Thanks again, and once again, I'm sorry I tuned out and didn't offer this
feedback before you revised the KIP.
-John
On Mon, Jun 22, 2020, at 06:11, Jorge Esteban Quilcate Otoya wrote:
> Hi everyone,
>
> I've updated the KIP, applying Matthias' feedback regarding interface
> hierarchy.
>
> Also, following the last email, I think we can consider reverse operations
> on KeyValue range as well, as implementation supports lexicographic order.
>
> I considered different naming between Key-based ranges and Time-based
> ranges, and mitigate confusion when fetching keys and time ranges as
> WindowStore does:
>
> Key-based ranges: reverseRange(), reverseAll()
> Time-based ranges: backwardFetch()
>
> Then, key-based changes apply to KeyValueStore, and time-based changes to
> Window and Session stores.
>
> Let me know if you have any questions.
>
> Thanks,
> Jorge.
>
>
> On Tue, Jun 16, 2020 at 12:47 AM Jorge Esteban Quilcate Otoya <
> quilcate.jo...@gmail.com> wrote:
>
> > Hi everyone, sorry for the late reply.
> >
> > Thanks Matthias for your feedback. I think it makes sense to reconsider
> > the current design based on your input.
> >
> > After digging deeper into the current implementation, I'd like to bring my
> > current understanding to be double-checked as it might be redefining the
> > KIP's scope:
> >
> > 1. There are 2 ranges been exposed by different stores:
> >
> > a. Key Range
> > b. Timestamp Range
> >
> > So far, we have discussed covering both.
> >
> > 2. Key Range functions do not provide ordering guarantees by design:
> >
> > ```ReadOnlyKeyValueStore.java
> > /**
> > * Get an iterator over a given range of keys. This iterator must be
> > closed after use.
> > * The returned iterator must be safe from {@link
> > java.util.ConcurrentModificationException}s
> > * and must not return null values. No ordering guarantees are
> > provided.
> > * ...
> > */
> > KeyValueIterator<K, V> range(K from, K to);
> > ```
> >
> > Therefore, I'd propose removing Key range operations from the scope.
> >
> > 3. Timestamp Range operations happen at the SegmentsStore level (internal)
> > API
> >
> > AFAICT, Segments wrappers handle all Timestamp ranges queries.
> >
> > I'd propose extending `Segments#segments(timeFrom, timeTo, backwards)`
> > with a flag for backwards operations.
> >
> > As segments returned will be processed backwards, I'm not extending
> > KeyValueStores to query each segment backwards as previous point 2.
> >
> > 4. Extend WindowStores implementations with a new
> > WindowBackwardStore/ReadOnlyBackwardStore:
> >
> > ```java
> > public interface ReadOnlyWindowBackwardStore<K, V> {
> > WindowStoreIterator<V> backwardFetch(K key, Instant from, Instant to)
> > throws IllegalArgumentException;
> >
> > KeyValueIterator<Windowed<K>, V> backwardFetch(K from, K to, Instant
> > fromTime, Instant toTime)
> > throws IllegalArgumentException;
> >
> > KeyValueIterator<Windowed<K>, V> backwardFetchAll(Instant from,
> > Instant to) throws IllegalArgumentException;
> > ```
> >
> > 5. SessionStore is a bit different as it has fetch/find sessions spread
> > between SessionStore and ReadOnlySessionStore.
> >
> > I'd propose a new interface `SessionBackwardStore` to expose backward find
> > operations:
> >
> > ```java
> > public interface SessionBackwardStore<K, AGG> {
> > KeyValueIterator<Windowed<K>, AGG> backwardFindSessions(final K key,
> > final long earliestSessionEndTime, final long latestSessionStartTime);
> >
> > KeyValueIterator<Windowed<K>, AGG> backwardFindSessions(final K
> > keyFrom, final K keyTo, final long earliestSessionEndTime, final long
> > latestSessionStartTime);
> > }
> > ```
> >
> > If this understanding is correct I'll proceed to update the KIP based on
> > this.
> >
> > Looking forward to your feedback.
> >
> > Thanks,
> > Jorge.
> >
> > On Fri, May 29, 2020 at 3:32 AM Matthias J. Sax <mj...@apache.org> wrote:
> >
> >> Hey,
> >>
> >> Sorry that I am late to the game. I am not 100% convinced about the
> >> current proposal. Using a new config as feature flag seems to be rather
> >> "nasty" to me, and flipping from/to is a little bit too fancy for my
> >> personal taste.
> >>
> >> I agree, that the original proposal using a "ReadDirection" enum is not
> >> ideal either.
> >>
> >> Thus, I would like to put out a new idea: We could add a new interface
> >> that offers new methods that return revers iterators.
> >>
> >> The KIP already proposes to add `reverseAll()` and it seems backward
> >> incompatible to just add this method to `ReadOnlyKeyValueStore` and
> >> `ReadOnlyWindowStore`. I don't think we could provide a useful default
> >> implementation for custom stores and thus either break compatibility or
> >> need add a default that just throws an exception. Neither seems to be a
> >> good option.
> >>
> >> Using a new interface avoid this issue and allows users implementing
> >> custom stores to opt-in by adding the interface to their stores.
> >> Furthermore, we don't need any config. In the end, we encapsulte the
> >> change into the store, and our runtime is agnostic to it (as it should
> >> be).
> >>
> >> The hierarchy becomes a little complex (but uses would not really see
> >> the complexity):
> >>
> >> // exsiting
> >> ReadOnlyKeyValueStore
> >> KeyValueStore extend StateStore, ReadOnlyKeyValueStore
> >>
> >>
> >> // helper interface; users don't care
> >> // need similar ones for other stores
> >> ReverseReadOnlyKeyValueStore {
> >> KeyValueIterator<K, V> reverseRange(K from, K to);
> >> KeyValueIterator<K, V> reverseAll();
> >> }
> >>
> >>
> >> // two new user facing interfaces for kv-store
> >> // need similar ones for other stores
> >> ReadOnlyKeyValueStoreWithReverseIterators extends ReadOnlyKeyValueStore,
> >> ReverseReadOnlyKeyValueStore
> >>
> >> KeyValueStoreWithReverseIterators extends KeyValueStore,
> >> ReverseReadOnlyKeyValueStore
> >>
> >>
> >> // updated (also internal)
> >> // also need to update other built-in stores
> >> RocksDB implements KeyValueStoreWithReverseIterators, BulkLoadingStore
> >>
> >>
> >> In the end, user would only care about the two (for kv-case) new
> >> interface that offer revers iterator (read only and regular) and can
> >> cast stores accordingly in their Processors/Transformers or via IQ.
> >>
> >>
> >> Btw: if we add revers iterator for KeyValue and Window store, should we
> >> do the same for Session store?
> >>
> >>
> >>
> >> This might be more code to write, but I believe it provides the better
> >> user experience. Thoughts?
> >>
> >>
> >>
> >> -Matthias
> >>
> >>
> >>
> >>
> >> On 5/26/20 8:47 PM, John Roesler wrote:
> >> > Sorry for my silence, Jorge,
> >> >
> >> > I've just taken another look, and I'm personally happy with the KIP.
> >> >
> >> > Thanks,
> >> > -John
> >> >
> >> > On Tue, May 26, 2020, at 16:17, Jorge Esteban Quilcate Otoya wrote:
> >> >> If no additional comments, I will proceed to start the a vote thread.
> >> >>
> >> >> Thanks a lot for your feedback!
> >> >>
> >> >> On Fri, May 22, 2020 at 9:25 AM Jorge Esteban Quilcate Otoya <
> >> >> quilcate.jo...@gmail.com> wrote:
> >> >>
> >> >>> Thanks Sophie. I like the `reverseAll()` idea.
> >> >>>
> >> >>> I updated the KIP with your feedback.
> >> >>>
> >> >>>
> >> >>>
> >> >>> On Fri, May 22, 2020 at 4:22 AM Sophie Blee-Goldman <
> >> sop...@confluent.io>
> >> >>> wrote:
> >> >>>
> >> >>>> Hm, the case of `all()` does seem to present a dilemma in the case of
> >> >>>> variable-length keys.
> >> >>>>
> >> >>>> In the case of fixed-length keys, you can just compute the keys that
> >> >>>> correspond
> >> >>>> to the maximum and minimum serialized bytes, then perform a `range()`
> >> >>>> query
> >> >>>> instead of an `all()`. If your keys don't have a well-defined
> >> ordering
> >> >>>> such
> >> >>>> that
> >> >>>> you can't determine the MAX_KEY, then you probably don't care about
> >> the
> >> >>>> iterator order anyway.
> >> >>>>
> >> >>>> But with variable-length keys, there is no MAX_KEY. If all your
> >> keys were
> >> >>>> just
> >> >>>> of the form 'a', 'aa', 'aaaaa', 'aaaaaaa' then in fact the only way
> >> to
> >> >>>> figure out the
> >> >>>> maximum key in the store is by using `all()` -- and without a reverse
> >> >>>> iterator, you're
> >> >>>> doomed to iterate through every single key just to answer that simple
> >> >>>> question.
> >> >>>>
> >> >>>> That said, I still think determining the iterator order based on the
> >> >>>> to/from bytes
> >> >>>> makes a lot of intuitive sense and gives the API a nice symmetry.
> >> What if
> >> >>>> we
> >> >>>> solved the `all()` problem by just giving `all()` a reverse form to
> >> >>>> complement it?
> >> >>>> Ie we would have `all()` and `reverseAll()`, or something to that
> >> effect.
> >> >>>>
> >> >>>> On Thu, May 21, 2020 at 3:41 PM Jorge Esteban Quilcate Otoya <
> >> >>>> quilcate.jo...@gmail.com> wrote:
> >> >>>>
> >> >>>>> Thanks John.
> >> >>>>>
> >> >>>>> Agree. I like the first approach as well, with StreamsConfig flag
> >> >>>> passing
> >> >>>>> by via ProcessorContext.
> >> >>>>>
> >> >>>>> Another positive effect with "reverse parameters" is that in the
> >> case of
> >> >>>>> `fetch(keyFrom, keyTo, timeFrom, timeTo)` users can decide _which_
> >> pair
> >> >>>> to
> >> >>>>> flip, whether with `ReadDirection` enum it apply to both.
> >> >>>>>
> >> >>>>> The only issue I've found while reviewing the KIP is that `all()`
> >> won't
> >> >>>> fit
> >> >>>>> within this approach.
> >> >>>>>
> >> >>>>> We could remove it from the KIP and argue that for WindowStore,
> >> >>>>> `fetchAll(0, Long.MAX_VALUE)` can be used to get all in reverse
> >> order,
> >> >>>> and
> >> >>>>> for KeyValueStore, no ordering guarantees are provided.
> >> >>>>>
> >> >>>>> If there is consensus with this changes, I will go and update the
> >> KIP.
> >> >>>>>
> >> >>>>> On Thu, May 21, 2020 at 3:33 PM John Roesler <vvcep...@apache.org>
> >> >>>> wrote:
> >> >>>>>
> >> >>>>>> Hi Jorge,
> >> >>>>>>
> >> >>>>>> Thanks for that idea. I agree, a feature flag would protect anyone
> >> >>>>>> who may be depending on the current behavior.
> >> >>>>>>
> >> >>>>>> It seems better to locate the feature flag in the initialization
> >> >>>> logic of
> >> >>>>>> the store, rather than have a method on the "live" store that
> >> changes
> >> >>>>>> its behavior on the fly.
> >> >>>>>>
> >> >>>>>> It seems like there are two options here, one is to add a new
> >> config:
> >> >>>>>>
> >> >>>>>> StreamsConfig.ENABLE_BACKWARDS_ITERATION =
> >> >>>>>> "enable.backwards.iteration
> >> >>>>>>
> >> >>>>>> Or we can add a feature flag in Materialized, like
> >> >>>>>>
> >> >>>>>> Materialized.enableBackwardsIteration()
> >> >>>>>>
> >> >>>>>> I think I'd personally lean toward the config, for the following
> >> >>>> reason.
> >> >>>>>> The concern that Sophie raised is that someone's program may depend
> >> >>>>>> on the existing contract of getting an empty iterator. We don't
> >> want
> >> >>>> to
> >> >>>>>> switch behavior when they aren't expecting it, so we provide them a
> >> >>>>>> config to assert that they _are_ expecting the new behavior, which
> >> >>>>>> means they take responsibility for updating their code to expect
> >> the
> >> >>>> new
> >> >>>>>> behavior.
> >> >>>>>>
> >> >>>>>> There doesn't seem to be a reason to offer a choice of behaviors
> >> on a
> >> >>>>>> per-query, or per-store basis. We just want people to be not
> >> surprised
> >> >>>>>> by this change in general.
> >> >>>>>>
> >> >>>>>> What do you think?
> >> >>>>>> Thanks,
> >> >>>>>> -John
> >> >>>>>>
> >> >>>>>> On Wed, May 20, 2020, at 17:37, Jorge Quilcate wrote:
> >> >>>>>>> Thank you both for the great feedback.
> >> >>>>>>>
> >> >>>>>>> I like the "fancy" proposal :), and how it removes the need for
> >> >>>>>>> additional API methods. And with a feature flag on `StateStore`,
> >> >>>>>>> disabled by default, should no break current users.
> >> >>>>>>>
> >> >>>>>>> The only side-effect I can think of is that: by moving the flag
> >> >>>>> upwards,
> >> >>>>>>> all later operations become affected; which might be ok for most
> >> >>>> (all?)
> >> >>>>>>> cases. I can't think of an scenario where this would be an issue,
> >> >>>> just
> >> >>>>>>> want to point this out.
> >> >>>>>>>
> >> >>>>>>> If moving to this approach, I'd like to check if I got this right
> >> >>>>> before
> >> >>>>>>> updating the KIP:
> >> >>>>>>>
> >> >>>>>>> - only `StateStore` will change by having a new method:
> >> >>>>>>> `backwardIteration()`, `false` by default to keep things
> >> compatible.
> >> >>>>>>> - then all `*Stores` will have to update their implementation
> >> based
> >> >>>> on
> >> >>>>>>> this flag.
> >> >>>>>>>
> >> >>>>>>>
> >> >>>>>>> On 20/05/2020 21:02, Sophie Blee-Goldman wrote:
> >> >>>>>>>>> There's no possibility that someone could be relying
> >> >>>>>>>>> on iterating over that range in increasing order, because that's
> >> >>>> not
> >> >>>>>> what
> >> >>>>>>>>> happens. However, they could indeed be relying on getting an
> >> >>>> empty
> >> >>>>>>>> iterator
> >> >>>>>>>>
> >> >>>>>>>> I just meant that they might be relying on the assumption that
> >> the
> >> >>>>>> range
> >> >>>>>>>> query
> >> >>>>>>>> will never return results with decreasing keys. The empty
> >> iterator
> >> >>>>>> wouldn't
> >> >>>>>>>> break that contract, but of course a surprise reverse iterator
> >> >>>> would.
> >> >>>>>>>>
> >> >>>>>>>> FWIW I actually am in favor of automatically converting to a
> >> >>>> reverse
> >> >>>>>>>> iterator,
> >> >>>>>>>> I just thought we should consider whether this should be off by
> >> >>>>>> default or
> >> >>>>>>>> even possible to disable at all.
> >> >>>>>>>>
> >> >>>>>>>> On Tue, May 19, 2020 at 7:42 PM John Roesler <
> >> vvcep...@apache.org
> >> >>>>>
> >> >>>>>> wrote:
> >> >>>>>>>>
> >> >>>>>>>>> Thanks for the response, Sophie,
> >> >>>>>>>>>
> >> >>>>>>>>> I wholeheartedly agree we should take as much into account as
> >> >>>>> possible
> >> >>>>>>>>> up front, rather than regretting our decisions later. I actually
> >> >>>> do
> >> >>>>>> share
> >> >>>>>>>>> your vague sense of worry, which was what led me to say
> >> initially
> >> >>>>>> that I
> >> >>>>>>>>> thought my counterproposal might be "too fancy". Sometimes, it's
> >> >>>>>> better
> >> >>>>>>>>> to be explicit instead of "elegant", if we think more people
> >> >>>> will be
> >> >>>>>>>>> confused
> >> >>>>>>>>> than not.
> >> >>>>>>>>>
> >> >>>>>>>>> I really don't think that there's any danger of "relying on a
> >> >>>> bug"
> >> >>>>>> here,
> >> >>>>>>>>> although
> >> >>>>>>>>> people certainly could be relying on current behavior. One thing
> >> >>>> to
> >> >>>>> be
> >> >>>>>>>>> clear
> >> >>>>>>>>> about (which I just left a more detailed comment in KAFKA-8159
> >> >>>>> about)
> >> >>>>>> is
> >> >>>>>>>>> that
> >> >>>>>>>>> when we say something like key1 > key2, this ordering is defined
> >> >>>> by
> >> >>>>>> the
> >> >>>>>>>>> serde's output and nothing else.
> >> >>>>>>>>>
> >> >>>>>>>>> Currently, thanks to your fix in
> >> >>>>>> https://github.com/apache/kafka/pull/6521
> >> >>>>>>>>> ,
> >> >>>>>>>>> the store contract is that for range scans, if from > to, then
> >> >>>> the
> >> >>>>>> store
> >> >>>>>>>>> must
> >> >>>>>>>>> return an empty iterator. There's no possibility that someone
> >> >>>> could
> >> >>>>> be
> >> >>>>>>>>> relying
> >> >>>>>>>>> on iterating over that range in increasing order, because that's
> >> >>>> not
> >> >>>>>> what
> >> >>>>>>>>> happens. However, they could indeed be relying on getting an
> >> >>>> empty
> >> >>>>>>>>> iterator.
> >> >>>>>>>>>
> >> >>>>>>>>> My counterproposal was to actually change this contract to say
> >> >>>> that
> >> >>>>>> the
> >> >>>>>>>>> store
> >> >>>>>>>>> must return an iterator over the keys in that range, but in the
> >> >>>>>> reverse
> >> >>>>>>>>> order.
> >> >>>>>>>>> So, in addition to considering whether this idea is "too fancy"
> >> >>>> (aka
> >> >>>>>>>>> confusing),
> >> >>>>>>>>> we should also consider the likelihood of breaking an existing
> >> >>>>>> program with
> >> >>>>>>>>> this behavior/contract change.
> >> >>>>>>>>>
> >> >>>>>>>>> To echo your clarification, I'm also not advocating strongly in
> >> >>>>> favor
> >> >>>>>> of my
> >> >>>>>>>>> proposal. I just wanted to present it for consideration
> >> alongside
> >> >>>>>> Jorge's
> >> >>>>>>>>> original one.
> >> >>>>>>>>>
> >> >>>>>>>>> Thanks for raising these very good points,
> >> >>>>>>>>> -John
> >> >>>>>>>>>
> >> >>>>>>>>> On Tue, May 19, 2020, at 20:49, Sophie Blee-Goldman wrote:
> >> >>>>>>>>>>> Rather than working around it, I think we should just fix it
> >> >>>>>>>>>> Now *that's* a "fancy" idea :P
> >> >>>>>>>>>>
> >> >>>>>>>>>> That was my primary concern, although I do have a vague sense
> >> of
> >> >>>>>> worry
> >> >>>>>>>>>> that we might be allowing users to get into trouble without
> >> >>>>>> realizing it.
> >> >>>>>>>>>> For example if their custom serdes suffer a similar bug as the
> >> >>>>> above,
> >> >>>>>>>>>> and/or
> >> >>>>>>>>>> they rely on getting results in increasing order (of the keys)
> >> >>>> even
> >> >>>>>> when
> >> >>>>>>>>>> to < from. Maybe they're relying on the fact that the range
> >> >>>> query
> >> >>>>>> returns
> >> >>>>>>>>>> nothing in that case.
> >> >>>>>>>>>>
> >> >>>>>>>>>> Not sure if that qualifies as relying on a bug or not, but in
> >> >>>> that
> >> >>>>>> past
> >> >>>>>>>>>> we've
> >> >>>>>>>>>> taken the stance that we should not break compatibility even if
> >> >>>> the
> >> >>>>>> user
> >> >>>>>>>>>> was relying on bugs or unintentional behavior.
> >> >>>>>>>>>>
> >> >>>>>>>>>> Just to clarify I'm not advocating strongly against this
> >> >>>> proposal,
> >> >>>>>> just
> >> >>>>>>>>>> laying
> >> >>>>>>>>>> out some considerations we should take into account. At the end
> >> >>>> of
> >> >>>>>> the
> >> >>>>>>>>> day
> >> >>>>>>>>>> we should do what's right rather than maintain compatibility
> >> >>>> with
> >> >>>>>>>>> existing
> >> >>>>>>>>>> bugs, but sometimes there's a reasonable middle ground.
> >> >>>>>>>>>>
> >> >>>>>>>>>> On Tue, May 19, 2020 at 6:15 PM John Roesler <
> >> >>>> vvcep...@apache.org>
> >> >>>>>>>>> wrote:
> >> >>>>>>>>>>> Thanks Sophie,
> >> >>>>>>>>>>>
> >> >>>>>>>>>>> Woah, that’s a nasty bug. Rather than working around it, I
> >> >>>> think
> >> >>>>> we
> >> >>>>>>>>> should
> >> >>>>>>>>>>> just fix it. I’ll leave some comments on the Jira.
> >> >>>>>>>>>>>
> >> >>>>>>>>>>> It doesn’t seem like it should be this KIP’s concern that some
> >> >>>>>> serdes
> >> >>>>>>>>>>> might be incorrectly written.
> >> >>>>>>>>>>>
> >> >>>>>>>>>>> Were there other practical concerns that you had in mind?
> >> >>>>>>>>>>>
> >> >>>>>>>>>>> Thanks,
> >> >>>>>>>>>>> John
> >> >>>>>>>>>>>
> >> >>>>>>>>>>> On Tue, May 19, 2020, at 19:10, Sophie Blee-Goldman wrote:
> >> >>>>>>>>>>>> I like this "fancy idea" to just flip the to/from bytes but I
> >> >>>>> think
> >> >>>>>>>>> there
> >> >>>>>>>>>>>> are some practical limitations to implementing this. In
> >> >>>>> particular
> >> >>>>>>>>>>>> I'm thinking about this issue
> >> >>>>>>>>>>>> <https://issues.apache.org/jira/browse/KAFKA-8159> with the
> >> >>>>>> built-in
> >> >>>>>>>>>>> signed
> >> >>>>>>>>>>>> number serdes.
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> This trick would actually fix the problem for
> >> >>>> negative-negative
> >> >>>>>>>>> queries
> >> >>>>>>>>>>>> (ie where to & from are negative) but would cause
> >> undetectable
> >> >>>>>>>>>>>> incorrect results for negative-positive queries. For example,
> >> >>>> say
> >> >>>>>> you
> >> >>>>>>>>>>>> call #range with from = -1 and to = 1, using the Short
> >> serdes.
> >> >>>>> The
> >> >>>>>>>>>>>> serialized bytes for that are
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> from = 1111111111111111
> >> >>>>>>>>>>>> to = 0000000000000001
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> so we would end up flipping those and iterating over all keys
> >> >>>>> from
> >> >>>>>>>>>>>> 0000000000000001 to 1111111111111111. Iterating in
> >> >>>>> lexicographical
> >> >>>>>>>>>>>> order means we would iterate over every key in the space
> >> >>>> *except*
> >> >>>>>> for
> >> >>>>>>>>>>>> 0, but 0 is actually the *only* other key we meant to be
> >> >>>> included
> >> >>>>>> in
> >> >>>>>>>>> the
> >> >>>>>>>>>>>> range query.
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> Currently we just log a warning and return an empty iterator
> >> >>>> when
> >> >>>>>>>>>>>> to < from, which is obviously also incorrect but feels
> >> >>>> slightly
> >> >>>>>> more
> >> >>>>>>>>>>>> palatable. If we start automatically converting to reverse
> >> >>>>> queries
> >> >>>>>> we
> >> >>>>>>>>>>>> can't even log a warning in this case unless we wanted to log
> >> >>>> a
> >> >>>>>>>>> warning
> >> >>>>>>>>>>>> every time, which would be weird to do for a valid usage of a
> >> >>>> new
> >> >>>>>>>>>>>> feature.
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> All that said, I still like the idea overall. Off the top of
> >> >>>> my
> >> >>>>>> head
> >> >>>>>>>>> I
> >> >>>>>>>>>>> guess
> >> >>>>>>>>>>>> we could add a store config to enable/disable automatic
> >> >>>> reverse
> >> >>>>>>>>>>> iteration,
> >> >>>>>>>>>>>> which is off by default?
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> Thanks for the KIP! This will be a nice addition
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> Sophie
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> On Tue, May 19, 2020 at 3:21 PM John Roesler <
> >> >>>>> vvcep...@apache.org>
> >> >>>>>>>>>>> wrote:
> >> >>>>>>>>>>>>> Hi there Jorge,
> >> >>>>>>>>>>>>>
> >> >>>>>>>>>>>>> Thanks for the KIP!
> >> >>>>>>>>>>>>>
> >> >>>>>>>>>>>>> I think this feature sounds very reasonable.
> >> >>>>>>>>>>>>>
> >> >>>>>>>>>>>>> I'm not 100% sure if this is "too fancy", but what do you
> >> >>>> think
> >> >>>>>>>>>>>>> about avoiding the enum by instead allowing people to flip
> >> >>>>>>>>>>>>> the "from" and "to" endpoints? I.e., reading from "A" to "Z"
> >> >>>>> would
> >> >>>>>>>>>>>>> be a forward scan, and from "Z" to "A" would be a backward
> >> >>>> one?
> >> >>>>>>>>>>>>>
> >> >>>>>>>>>>>>> Thanks,
> >> >>>>>>>>>>>>> -John
> >> >>>>>>>>>>>>>
> >> >>>>>>>>>>>>> On Tue, May 19, 2020, at 16:20, Jorge Quilcate wrote:
> >> >>>>>>>>>>>>>> Hi everyone,
> >> >>>>>>>>>>>>>>
> >> >>>>>>>>>>>>>> I would like to start the discussion for KIP-617:
> >> >>>>>>>>>>>>>>
> >> >>>>>>>>>
> >> >>>>>>
> >> >>>>>
> >> >>>>
> >> https://cwiki.apache.org/confluence/display/KAFKA/KIP-617%3A+Allow+Kafka+Streams+State+Stores+to+be+iterated+backwards
> >> >>>>>>>>>>>>>> Looking forward to your feedback.
> >> >>>>>>>>>>>>>>
> >> >>>>>>>>>>>>>> Thanks!
> >> >>>>>>>>>>>>>> Jorge.
> >> >>>>>>>>>>>>>>
> >> >>>>>>>>>>>>>>
> >> >>>>>>>>>>>>>> Attachments:
> >> >>>>>>>>>>>>>> * 0x5F2C6E22064982DF.asc
> >> >>>>>>>
> >> >>>>>>>
> >> >>>>>>> Attachments:
> >> >>>>>>> * 0x5F2C6E22064982DF.asc
> >> >>>>>>
> >> >>>>>
> >> >>>>
> >> >>>
> >> >>
> >>
> >>
>
