<div dir="ltr"><br><br><div class="gmail_quote"><div dir="ltr">On Tue, Mar 28, 2017 at 12:52 PM Dan Berindei <<a href="mailto:dan.berindei@gmail.com">dan.berindei@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On Tue, Mar 28, 2017 at 6:44 PM, William Burns <<a href="mailto:mudokonman@gmail.com" class="gmail_msg" target="_blank">mudokonman@gmail.com</a>> wrote:<br class="gmail_msg">
><br class="gmail_msg">
><br class="gmail_msg">
> On Tue, Mar 28, 2017 at 11:24 AM Sanne Grinovero <<a href="mailto:sanne@infinispan.org" class="gmail_msg" target="_blank">sanne@infinispan.org</a>><br class="gmail_msg">
> wrote:<br class="gmail_msg">
>><br class="gmail_msg">
>> Hi Will,<br class="gmail_msg">
>><br class="gmail_msg">
>> I'm confused about the premise; when you state<br class="gmail_msg">
>><br class="gmail_msg">
>> " the Consumer is called while holding the lock for the given key and<br class="gmail_msg">
>> subsequently released after the Consumer operation completes."<br class="gmail_msg">
>><br class="gmail_msg">
>> What are the transaction boundaries?<br class="gmail_msg">
>> I see two options, please correct me so I understand:<br class="gmail_msg">
>><br class="gmail_msg">
>> A)<br class="gmail_msg">
>><br class="gmail_msg">
>> transaction.begin();<br class="gmail_msg">
>> cache.lockedStream().filterKeys(keys).filter(predicate).forEach(<br class="gmail_msg">
>> someOperation );<br class="gmail_msg">
>> transaction.commit(); <-- release all locks<br class="gmail_msg">
>><br class="gmail_msg">
>> B)<br class="gmail_msg">
>><br class="gmail_msg">
>> cache.lockedStream().filterKeys(keys).filter(predicate).forEach(<br class="gmail_msg">
>> transaction.begin();<br class="gmail_msg">
>> //to stuff on entry<br class="gmail_msg">
>> /transaction.commit(); <-- release this single entry's lock<br class="gmail_msg">
>> );<br class="gmail_msg">
><br class="gmail_msg">
><br class="gmail_msg">
> The user code doesn't really affect this, it is done internally by<br class="gmail_msg">
> Infinispan. We would acquire the lock on the user's behalf in the stream<br class="gmail_msg">
> operation then call the user's accept method. Then after they return we<br class="gmail_msg">
> would unlock the lock. The way I have it implemented at the moment in my PoC<br class="gmail_msg">
> (which could change) is I don't even start a transaction. It just locks the<br class="gmail_msg">
> key and then if the user were to invoke an operation that requires a<br class="gmail_msg">
> transaction it adds the lock owner to their tx context at that point so they<br class="gmail_msg">
> have ownership of the key.<br class="gmail_msg">
><br class="gmail_msg">
> Also to note that a commit or rollback in the Consumer currently doesn't<br class="gmail_msg">
> release the lock on the key. Although this could be discussed to be possibly<br class="gmail_msg">
> changed.<br class="gmail_msg">
><br class="gmail_msg">
<br class="gmail_msg">
With a transactional cache I was assuming you manage the transaction<br class="gmail_msg">
yourself... if the user has to call<br class="gmail_msg">
transactionManager.begin()/commit()/rollback() anyway, why not use a<br class="gmail_msg">
regular stream?<br class="gmail_msg"></blockquote><div><br></div><div>The user would be using an implicit transaction or explicit. Like I said this is up for discussion. The main reason I am staying away from managing the transaction is that the user can mess with the transaction as well which would possibly release the lock. It is much simpler if all I am doing is managing the lock. And if the user doesn't require a transaction in Infinispan we didn't waste time starting one and releasing one.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br class="gmail_msg">
>><br class="gmail_msg">
>><br class="gmail_msg">
>><br class="gmail_msg">
>> I think it's important to clarify this as I suspect that #A is not<br class="gmail_msg">
>> implementable within reasonable guarantees, while in the case of B# I<br class="gmail_msg">
>> see no use for optimistic locking *from a user's perspective*.<br class="gmail_msg">
><br class="gmail_msg">
><br class="gmail_msg">
> Exactly my thoughts regarding optimistic. I don't think #A is even feasible<br class="gmail_msg">
> given constraints of having a distributed transaction like this.<br class="gmail_msg">
><br class="gmail_msg">
<br class="gmail_msg">
Totally agree that #A can't work with any kind of transaction configuration.<br class="gmail_msg">
<br class="gmail_msg">
As to optimistic locking, I would like having "feature parity" between<br class="gmail_msg">
pessimistic and optimistic caches as much as possible, but I agree<br class="gmail_msg">
locking eagerly and retrying the consumer on WriteSkewException are a<br class="gmail_msg">
bit too different to fit under the same API.<br class="gmail_msg"></blockquote><div><br></div><div>Yeah I would definitely like to have it as well, but I just can't see how it fits in. This is despite the implementation detail that it is quite difficult to get it working currently :D</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br class="gmail_msg">
>><br class="gmail_msg">
>><br class="gmail_msg">
>> Also: what kind of guarantees do you expect about having the operation<br class="gmail_msg">
>> being applied on some entry which is strictly *still* a subset of the<br class="gmail_msg">
>> keys as defined by the filter predicates?<br class="gmail_msg">
>> I take it you'd want to acquire the locks during the filtering process?<br class="gmail_msg">
><br class="gmail_msg">
><br class="gmail_msg">
> That is a good question. I hadn't thought about the details but what I had<br class="gmail_msg">
> implemented was we have to first read the entry, lock the key, reread the<br class="gmail_msg">
> entry (in case of concurrent update) and then finally call their Predicate.<br class="gmail_msg">
> Another reason the filterKeys is much more efficient :) Note this read,<br class="gmail_msg">
> locking and reread is done even without a Predicate supplied. And actually I<br class="gmail_msg">
> can also optimize filterKeys to not do the initial read since we already<br class="gmail_msg">
> have the key.<br class="gmail_msg">
><br class="gmail_msg">
<br class="gmail_msg">
Would this be more efficient than the consumer reading the key with<br class="gmail_msg">
FORCE_WRITE_LOCK and deciding what to do based on the value?<br class="gmail_msg">
<br class="gmail_msg"></blockquote><div><br></div><div>The problem with this is you have to go remote to lock the key, return the value then do something for every key (not to mention pulling those keys using an iterator). Very costly! The main benefit of the stream with lock is that you are performing everything on the primary owner of the data with the lock already acquired. The only piece sent remotely is the consumer and some internal classes, very light weight and you have all the benefits of data locality.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
>><br class="gmail_msg">
>><br class="gmail_msg">
>> That would require the move the transaction boundary to the scenario<br class="gmail_msg">
>> A# which seems undesirable.<br class="gmail_msg">
>> Technically if I were to need something like this I guess I'd expect<br class="gmail_msg">
>> to have a user experience akin to B# but have Infinispan essentially<br class="gmail_msg">
>> use optimistic locking (and auto-skip) on entries which are mutated<br class="gmail_msg">
>> and fall out of the filter predicate during the lock attempt.<br class="gmail_msg">
>><br class="gmail_msg">
>> Essentially I suspect that we'd not want to implement different<br class="gmail_msg">
>> versions of this depending on the transaction mode, but figure out the<br class="gmail_msg">
>> use case and implement a one and only transaction mode which suites<br class="gmail_msg">
>> such use cases. So for example we'd simply not offer a mode which<br class="gmail_msg">
>> requires to copy the whole grid into the current TX context.<br class="gmail_msg">
><br class="gmail_msg">
><br class="gmail_msg">
> This was never the intent and in my follow up emails I came to what seems<br class="gmail_msg">
> like the same conclusion that basically this can't be done with the user<br class="gmail_msg">
> controlling the transaction and it doesn't really make sense in an<br class="gmail_msg">
> optimistic transaction (since you are already at that node, you are already<br class="gmail_msg">
> doing everything pessimistically).<br class="gmail_msg">
><br class="gmail_msg">
<br class="gmail_msg">
Even local caches can use optimistic locking :)<br class="gmail_msg"></blockquote><div><br></div><div>Yes I know :) I was just framing it in the notion of remote. If anyone can think of a nice way of using this with optimistic transactions I would all be for it. But optimistic transactions just doesn't make any sense to me when you are locking a key eagerly for someone to do something with it (definition of pessimistic transaction).</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br class="gmail_msg">
>><br class="gmail_msg">
>><br class="gmail_msg">
>> Thanks,<br class="gmail_msg">
>> Sanne<br class="gmail_msg">
>><br class="gmail_msg">
>><br class="gmail_msg">
>><br class="gmail_msg">
>> On 28 March 2017 at 14:49, William Burns <<a href="mailto:mudokonman@gmail.com" class="gmail_msg" target="_blank">mudokonman@gmail.com</a>> wrote:<br class="gmail_msg">
>> ><br class="gmail_msg">
>> ><br class="gmail_msg">
>> > On Mon, Mar 27, 2017 at 9:02 PM Galder Zamarreño <<a href="mailto:galder@redhat.com" class="gmail_msg" target="_blank">galder@redhat.com</a>><br class="gmail_msg">
>> > wrote:<br class="gmail_msg">
>> >><br class="gmail_msg">
>> >><br class="gmail_msg">
>> >> --<br class="gmail_msg">
>> >> Galder Zamarreño<br class="gmail_msg">
>> >> Infinispan, Red Hat<br class="gmail_msg">
>> >><br class="gmail_msg">
>> >> > On 21 Mar 2017, at 17:16, Dan Berindei <<a href="mailto:dan.berindei@gmail.com" class="gmail_msg" target="_blank">dan.berindei@gmail.com</a>><br class="gmail_msg">
>> >> > wrote:<br class="gmail_msg">
>> >> ><br class="gmail_msg">
>> >> > I'm leaning towards option 1.<br class="gmail_msg">
>> >> ><br class="gmail_msg">
>> >> > Are you thinking about also allowing the consumer to modify the<br class="gmail_msg">
>> >> > entry,<br class="gmail_msg">
>> >> > like JCache's EntryProcessors? For a consumer that can only modify<br class="gmail_msg">
>> >> > the<br class="gmail_msg">
>> >> > current entry, we could even "emulate" locking in an optimistic cache<br class="gmail_msg">
>> >> > by catching the WriteSkewException and running the consumer again.<br class="gmail_msg">
>> >> ><br class="gmail_msg">
>> >> > I wouldn't allow this to be mixed with other operations in a stream,<br class="gmail_msg">
>> >> > because then you may have to run filters/mappers/sorting while<br class="gmail_msg">
>> >> > holding<br class="gmail_msg">
>> >> > the lock as well.<br class="gmail_msg">
>> >><br class="gmail_msg">
>> >> ^ Would forEach w/ lock still run for all entries in originator? If so,<br class="gmail_msg">
>> >> not being able to filter could be a pain. IOW, you'd be forcing all<br class="gmail_msg">
>> >> entries<br class="gmail_msg">
>> >> to be shipped to a node and user to do its own filtering. Not ideal :\<br class="gmail_msg">
>> ><br class="gmail_msg">
>> ><br class="gmail_msg">
>> > No the primary owner would run the operation per entry. I was thinking<br class="gmail_msg">
>> > we<br class="gmail_msg">
>> > would have 2 levels of filtering in my proposal above.<br class="gmail_msg">
>> ><br class="gmail_msg">
>> > We would have the first one which is using filterKeys on the CacheStream<br class="gmail_msg">
>> > method. This requires serializing keys sent to each node (only primary<br class="gmail_msg">
>> > owned<br class="gmail_msg">
>> > keys are sent). While it has the cost of serialization it makes up for<br class="gmail_msg">
>> > by<br class="gmail_msg">
>> > having constant time lookups (no iterating memory/stores) for the keys<br class="gmail_msg">
>> > as it<br class="gmail_msg">
>> > creates a stream using Cache.get to populate it.<br class="gmail_msg">
>> ><br class="gmail_msg">
>> > The second was to support the filter method on the Stream API which<br class="gmail_msg">
>> > would<br class="gmail_msg">
>> > allow for a Predicate so you don't have to serialize keys. In this case<br class="gmail_msg">
>> > you<br class="gmail_msg">
>> > wouldn't want to include keys in this Predicate as all keys would be<br class="gmail_msg">
>> > serialized to all nodes and then you still have to iterate and check the<br class="gmail_msg">
>> > entire data container/store.<br class="gmail_msg">
>> ><br class="gmail_msg">
>> > You could actually do both as well. So if you only want a subset of<br class="gmail_msg">
>> > known<br class="gmail_msg">
>> > keys where their values match a Predicate this can be done too.<br class="gmail_msg">
>> ><br class="gmail_msg">
>> > cache.lockedStream().filterKeys(keys).filter(predicate).forEach();<br class="gmail_msg">
>> ><br class="gmail_msg">
>> >><br class="gmail_msg">
>> >><br class="gmail_msg">
>> >><br class="gmail_msg">
>> >> ><br class="gmail_msg">
>> >> > Cheers<br class="gmail_msg">
>> >> > Dan<br class="gmail_msg">
>> >> ><br class="gmail_msg">
>> >> ><br class="gmail_msg">
>> >> > On Tue, Mar 21, 2017 at 5:37 PM, William Burns <<a href="mailto:mudokonman@gmail.com" class="gmail_msg" target="_blank">mudokonman@gmail.com</a>><br class="gmail_msg">
>> >> > wrote:<br class="gmail_msg">
>> >> >> Some users have expressed the need to have some sort of forEach<br class="gmail_msg">
>> >> >> operation<br class="gmail_msg">
>> >> >> that is performed where the Consumer is called while holding the<br class="gmail_msg">
>> >> >> lock<br class="gmail_msg">
>> >> >> for<br class="gmail_msg">
>> >> >> the given key and subsequently released after the Consumer operation<br class="gmail_msg">
>> >> >> completes.<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> Due to the nature of how streams work with retries and performing<br class="gmail_msg">
>> >> >> the<br class="gmail_msg">
>> >> >> operation on the primary owner, this works out quite well with<br class="gmail_msg">
>> >> >> forEach<br class="gmail_msg">
>> >> >> to be<br class="gmail_msg">
>> >> >> done in an efficient way.<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> The problem is that this only really works well with non tx and<br class="gmail_msg">
>> >> >> pessimistic<br class="gmail_msg">
>> >> >> tx. This obviously leaves out optimistic tx, which at first I was a<br class="gmail_msg">
>> >> >> little<br class="gmail_msg">
>> >> >> worried about. But after thinking about it more, this prelocking and<br class="gmail_msg">
>> >> >> optimistic tx don't really fit that well together anyways. So I am<br class="gmail_msg">
>> >> >> thinking<br class="gmail_msg">
>> >> >> whenever this operation is performed it would throw an exception not<br class="gmail_msg">
>> >> >> letting<br class="gmail_msg">
>> >> >> the user use this feature in optimistic transactions.<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> Another question is what does the API for this look like. I was<br class="gmail_msg">
>> >> >> debating<br class="gmail_msg">
>> >> >> between 3 options myself:<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> 1. AdvancedCache.forEachWithLock(BiConsumer<Cache, CacheEntry<K, V>><br class="gmail_msg">
>> >> >> consumer)<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> This require the least amount of changes, however the user can't<br class="gmail_msg">
>> >> >> customize<br class="gmail_msg">
>> >> >> certain parameters that CacheStream currently provides (listed below<br class="gmail_msg">
>> >> >> -<br class="gmail_msg">
>> >> >> big<br class="gmail_msg">
>> >> >> one being filterKeys).<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> 2. CacheStream.forEachWithLock(BiConsumer<Cache, CacheEntry<K, V>><br class="gmail_msg">
>> >> >> consumer)<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> This method would only be allowed to be invoked on the Stream if no<br class="gmail_msg">
>> >> >> other<br class="gmail_msg">
>> >> >> intermediate operations were invoked, otherwise an exception would<br class="gmail_msg">
>> >> >> be<br class="gmail_msg">
>> >> >> thrown. This still gives us access to all of the CacheStream methods<br class="gmail_msg">
>> >> >> that<br class="gmail_msg">
>> >> >> aren't on the Stream interface (ie. sequentialDistribution,<br class="gmail_msg">
>> >> >> parallelDistribution, parallel, sequential, filterKeys,<br class="gmail_msg">
>> >> >> filterKeySegments,<br class="gmail_msg">
>> >> >> distributedBatchSize, disableRehashAware, timeout).<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> 3. LockedStream<CacheEntry<K, V>> AdvancedCache.lockedStream()<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> This requires the most changes, however the API would be the most<br class="gmail_msg">
>> >> >> explicit.<br class="gmail_msg">
>> >> >> In this case the LockedStream would only have the methods on it that<br class="gmail_msg">
>> >> >> are<br class="gmail_msg">
>> >> >> able to be invoked as noted above and forEach.<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> I personally feel that #3 might be the cleanest, but obviously<br class="gmail_msg">
>> >> >> requires<br class="gmail_msg">
>> >> >> adding more classes. Let me know what you guys think and if you<br class="gmail_msg">
>> >> >> think<br class="gmail_msg">
>> >> >> the<br class="gmail_msg">
>> >> >> optimistic exclusion is acceptable.<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> Thanks,<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> - Will<br class="gmail_msg">
>> >> >><br class="gmail_msg">
>> >> >> _______________________________________________<br class="gmail_msg">
>> >> >> infinispan-dev mailing list<br class="gmail_msg">
>> >> >> <a href="mailto:infinispan-dev@lists.jboss.org" class="gmail_msg" target="_blank">infinispan-dev@lists.jboss.org</a><br class="gmail_msg">
>> >> >> <a href="https://lists.jboss.org/mailman/listinfo/infinispan-dev" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.jboss.org/mailman/listinfo/infinispan-dev</a><br class="gmail_msg">
>> >> > _______________________________________________<br class="gmail_msg">
>> >> > infinispan-dev mailing list<br class="gmail_msg">
>> >> > <a href="mailto:infinispan-dev@lists.jboss.org" class="gmail_msg" target="_blank">infinispan-dev@lists.jboss.org</a><br class="gmail_msg">
>> >> > <a href="https://lists.jboss.org/mailman/listinfo/infinispan-dev" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.jboss.org/mailman/listinfo/infinispan-dev</a><br class="gmail_msg">
>> >><br class="gmail_msg">
>> >><br class="gmail_msg">
>> >> _______________________________________________<br class="gmail_msg">
>> >> infinispan-dev mailing list<br class="gmail_msg">
>> >> <a href="mailto:infinispan-dev@lists.jboss.org" class="gmail_msg" target="_blank">infinispan-dev@lists.jboss.org</a><br class="gmail_msg">
>> >> <a href="https://lists.jboss.org/mailman/listinfo/infinispan-dev" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.jboss.org/mailman/listinfo/infinispan-dev</a><br class="gmail_msg">
>> ><br class="gmail_msg">
>> ><br class="gmail_msg">
>> > _______________________________________________<br class="gmail_msg">
>> > infinispan-dev mailing list<br class="gmail_msg">
>> > <a href="mailto:infinispan-dev@lists.jboss.org" class="gmail_msg" target="_blank">infinispan-dev@lists.jboss.org</a><br class="gmail_msg">
>> > <a href="https://lists.jboss.org/mailman/listinfo/infinispan-dev" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.jboss.org/mailman/listinfo/infinispan-dev</a><br class="gmail_msg">
>><br class="gmail_msg">
>> _______________________________________________<br class="gmail_msg">
>> infinispan-dev mailing list<br class="gmail_msg">
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>> <a href="https://lists.jboss.org/mailman/listinfo/infinispan-dev" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.jboss.org/mailman/listinfo/infinispan-dev</a><br class="gmail_msg">
><br class="gmail_msg">
><br class="gmail_msg">
> _______________________________________________<br class="gmail_msg">
> infinispan-dev mailing list<br class="gmail_msg">
> <a href="mailto:infinispan-dev@lists.jboss.org" class="gmail_msg" target="_blank">infinispan-dev@lists.jboss.org</a><br class="gmail_msg">
> <a href="https://lists.jboss.org/mailman/listinfo/infinispan-dev" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.jboss.org/mailman/listinfo/infinispan-dev</a><br class="gmail_msg">
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