On Thu, Jun 29, 2017 at 11:53 AM, Radim Vansa <rva...@redhat.com> wrote: > On 06/28/2017 04:20 PM, Dan Berindei wrote: >> On Wed, Jun 28, 2017 at 2:17 PM, Radim Vansa <rva...@redhat.com> wrote: >>> On 06/28/2017 10:40 AM, Dan Berindei wrote: >>>> On Wed, Jun 28, 2017 at 10:17 AM, Radim Vansa <rva...@redhat.com> wrote: >>>>> On 06/27/2017 03:54 PM, Dan Berindei wrote: >>>>>> On Tue, Jun 27, 2017 at 2:43 PM, Adrian Nistor <anis...@redhat.com> >>>>>> wrote: >>>>>>> I've said this in a previous thread on this same issue, I will repeat >>>>>>> myself >>>>>>> as many times as needed. >>>>>>> >>>>>>> Continuous queries require the previous value itself, not just >>>>>>> knowledge of >>>>>>> the type of the previous value. Strongly typed caches solve no problem >>>>>>> here. >>>>>>> >>>>>>> So if we half-fix query but leave CQ broken I will be half-happy (ie. >>>>>>> very >>>>>>> depressed) :) >>>>>>> >>>>>>> I'd remove these commands completely or possibly remove them just from >>>>>>> public API and keep them internal. >>>>>>> >>>>>> +1 to remove the flags from the public API. Most of them are not safe >>>>>> for applications to use, and ignoring them when they can lead to >>>>>> inconsistencies would make them useless. >>>>>> >>>>>> E.g. the whole point of SKIP_INDEX_CLEANUP is that the cache doesn't >>>>>> know when it is safe to skip the delete statement, and it relies on >>>>>> the application making a (possibly wrong) choice. >>>>>> >>>>>> IGNORE_RETURN_VALUES should be safe to use, and we actually recommend >>>>>> that applications use it right now. If query or listeners need the >>>>>> previous value, then we should load it internally, but hide it from >>>>>> the user. >>>>>> >>>>>> But removing it opens another discussion: should we replace it in the >>>>>> public API with a new method AdvancedCache.ignoreReturnValues(), or >>>>>> should we make it the default and add a method >>>>>> AdvancedCache.forceReturnPreviousValues()? >>>>> Please don't derail the thread. >>>>> >>>> I don't think I'm derailing the thread: IGNORE_PREVIOUS_VALUES also >>>> breaks the previous value for listeners, even if the QueryInterceptor >>>> removes it from write commands. And it is public (+recommended) API, >>>> in fact most if not all of our performance tests use it. >>> That's just a flawed implementation. IPV is documented to be a 'safe' >>> flag that should affect mostly primary -> origin replication, all the >>> other is implementation. And we can fix that. Users should *not* expect >>> that it e.g. skips loading from a cache store. We have already removed >>> the modes that would be broken-by-design. >>> >> I think you're confusing IGNORE_RETURN_VALUES with SKIP_REMOTE_LOOKUP >> here. The IVR javadoc doesn't say anything about remote lookups, only >> SRL does. > > No, I am not; While IRV does not mention the replication, it's said to > be 'safe'. So omitting the primary -> origin replication is basically > all it can do when listeners are in place. You're right that I have > missed the second part in SRL talking about put()s; I took it as a flag > prohibiting any remote lookup (as the RPC operation in its whole) any > time the remote value is needed. Yes, the second part seems equal to my > understanding of IRV. > >> >> And I agree that the current status is far from ideal, but there is >> one more valid alternative: we can decide that the previous value is >> only reliable in clustered listeners, and local listeners don't always >> have it. Document that, make sure continuous query uses clustered >> listeners, and we're done :) > > Unreliable return values are worse than none; I would rather remove them > if we can't guarantee that these are right. Though, clustered listeners > are based on regular listeners, so you'd need some means to make them > reliable.
We could change the clustered listeners so that they're not based on the regular listeners... I've been pestering Will about this ever since the clustered listeners landed! But I should have been clearer: I didn't mean that the listeners on the backups should receive the previous value whenever we feel like it, I meant we should document and enforce that the previous value is only included in the event for listeners on the primary owner. >>> On the other hand, write-only commands are not about *returning* the >>> value but about (not) *reading* it, therefore (in my eyes) user could >>> make that assumption and would like to enforce it this way. Even some >>> docs explaining PersistenceMode.SKIP suggest that. >>> >> To me the purpose the same, there is no difference between returning >> the previous value to the application or providing the previous value >> via EntryView. > > There is a difference between what's provided locally and what's send > over the network. > >> Applying this logic to the JCache API, it would mean >> put() should never read the previous value, because some users could >> assume that only getAndPut() reads it. > > OK, this is a valid point. > >> >> In the old times we didn't have IGNORE_RETURN_VALUES, only >> SKIP_REMOTE_LOOKUP+SKIP_CACHE_LOAD, and they would sometimes be >> ignored (e.g. if the write was conditional). I think that's what >> Galder had in mind when he wrote the PersistenceMode api note, not the >> current behaviour of SKIP_CACHE_LOAD. I'll let Galder clarify this >> himself, but I'll be very disappointed if he says he designed the >> write-only operations so that they'll never work with query. >> >> >>> I don't want to talk about flags, because I see all flags but IPV as >>> 'effectively internal'. Let's discuss it more high-level. Some API >>> exposes non-reading operation - we can see that under some circumstances >>> this is not possible so we have options to 1) break stuff 2) break API >>> assumptions 3) sometimes break API assumptions 4) remove such API (to >>> not allow the user to make such assumptions). There's also an option 5) >>> to fail the operation if the API assumption would be broken. Though, I >>> don't fancy getting exception from a WriteOnlyMap.eval just because >>> someone has registered a listener. >>> >> I disagree with the premise: there's no good reason for the user to >> assume that write-only commands are *guaranteed* to never load the >> previous value from a store. We just need to add a clarification to >> the write-only operations' javadoc, no need to break anything. > > OK then, though it diminishes the value of write-only commands a lot. > >> >> >>>> For that matter, ClusteredCacheLoaderInterceptor also doesn't load the >>>> previous value on backup owners for most write commands >>>> (LoadType.PRIMARY), we'd need to change that as well. >>> Yes, all commands will have to load current value on all owners. >>> >>>>>>> On 06/27/2017 01:28 PM, Sanne Grinovero wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>> On 27 Jun 2017 10:13, "Radim Vansa" <rva...@redhat.com> wrote: >>>>>>> >>>>>>> Hi, >>>>>>> >>>>>>> I am working on entry version history (again). In Como we've discussed >>>>>>> that previous values are needed for (continuous) query and reliable >>>>>>> listeners, >>>>>>> >>>>>>> >>>>>>> Index based queries also require the previous value on a write - unless >>>>>>> we >>>>>>> can get "strongly typed caches" giving guarantees about the class to >>>>>>> represent the content of a cache to be unique. >>>>>>> >>>>>>> Essentially we only need to know the type of the previous object. It >>>>>>> might >>>>>>> be worth having a way to load the type metadata if the previous value >>>>>>> only. >>>>>>> >>>>>>> so I wonder what should we do with functional write-only >>>>>>> commands. These are different to commands with flags, because flags >>>>>>> (other than ignore return value) are expected to break something. >>>>>>> >>>>>>> >>>>>>> Sorry I hope to not derail the thread but let's remind that we hope to >>>>>>> evolve beyond "flags are expected to break stuff" ; we never got to it >>>>>>> but >>>>>>> search the mailing list. >>>>>>> >>>>>>> Since flags are exposed to the user I would rather they're not allowed >>>>>>> to >>>>>>> break things. >>>>>>> Could they be treated as hints? Ignore the flag (and warn?) if the used >>>>>>> configuration/integrations veto them. >>>>>>> >>>>>>> Alternatively, let's remove them from API. Remember "The Jokre" POC was >>>>>>> intentionally designed to explore pushing the limits on performance w/o >>>>>>> end >>>>>>> users having to solve puzzles, such as learning details about these >>>>>>> flags >>>>>>> and their possible side effects. >>>>>>> >>>>>>> So assuming they become either "safe" or internal, maybe you can take >>>>>>> advantage of them? >>>>>>> >>>>>>> I see >>>>>>> the available options as: >>>>>>> >>>>>>> 1) run write-only commands 'optimized', ignoring any querying and such >>>>>>> (warn user that he will break it) >>>>>>> >>>>>>> 2) run write-only without any optimization, rendering them useless >>>>>>> >>>>>>> 3) detect when querying is set up (ignoring listeners and maybe other >>>>>>> stuff that could get broken) >>>>>>> >>>>>>> >>>>>>> Might be useful for making a POC work, but I believe query will be very >>>>>>> likely to be often enabled. >>>>>>> Having an either / or switch for different features in Infinispan will >>>>>>> make >>>>>>> it harder to use and understand, so I'd rather see work on the right >>>>>>> design >>>>>>> as taking temporary shortcuts risks baking into stone features which we >>>>>>> later struggle to fix or maintain. >>>>>>> >>>>>> I vote for this option. >>>>>> >>>>>> Query, listeners, and other components that need the previous value >>>>>> should not just assume that the application knows better, they should >>>>>> be able to change how operations works based on their needs. Of >>>>>> course, the reverse is also true: if the application uses write-only >>>>>> commands (or IGNORE_RETURN_VALUES) for performance reasons, it should >>>>>> be possible for the user to detect why the previous values are still >>>>>> loaded. >>>>> If it were just query (static configuration), I would be okay with this >>>>> idea. But as per listeners - besides tainting the design (event source >>>>> should not check if there's a listener) you'd need to check *before* >>>> The source wouldn't check for listeners explicitly, the notifier would >>>> have an isPreviousValueNeeded() method and precompute that before a >>>> listener is added or after a listener is removed. I was am assuming >>>> some listeners will not need the previous value, e.g. the listeners >>>> installed by streams. >>> You can cover your warts with a make-up but you'll still have warts :) >> Cutting them off doesn't necessarily work, either :) > > Yep, some people tend to fix w/ hacks instead of designing :) > >> >>>>> (DistributionI, CacheLoaderI) you have to call notify (cmd.perform, >>>>> EWI). So this is a space for race conditions or weird handling (if >>>>> there's a listener when I am about to call notify and my flags are not >>>>> cleared, skip the notification and pretend that this code was invoked >>>>> before the listener was registered...). Or do you have another solution >>>>> in mind (config option to disable listeners && all features using those?). >>>>> >>>> I was definitely going for the weird handling... >>>> >>>> My plan was to set a HAS_PREVIOUS_VALUE flag on the context entry when >>>> it's loaded, and check that before invoking a listener that needs the >>>> previous value. It is missing one edge case: if one thread starts a >>>> write operation, then another thread installs a listener that requires >>>> the previous value and iterates over the cache, the second thread may >>>> not see the value written by the first thread. >>> If the operations overlap, you could pretend that the write has finished >>> before the listener was invoked and simply not notify the listener. If I >>> am missing it please write it down in code. But handling this in any way >>> is still clumsy. >> I hope pseudo-code is fine... >> >> 1. cache.put(k, v1) starts, doesn't load the previous value v0 in the context >> 2. cache.addListener(l) runs, doesn't block >> 3. cache.entrySet().forEach() runs, finds k->v0 >> 4. cache.put(k, v1) commits k->v1, should notify the listener but >> doesn't have the previous value >> 5. cache.put(k, v0) returns, but the code that installed the listener >> thinks the value of k is still v0 > > Oh OK, I should have drawn that myself when considering the scenario. > You're right, here we'll have to retry. > > All in all, I think this discussion is done. We'll tell users to stick > their flags where the sun doesn't shine and remove any inconvenient > ones. Should we issue a warning any time we're removing the flag? > If you mean that we should remove the flags from the public API, I agree. If you mean we should just ignore them, then no, because most of the flags were added for internal components that really need their semantics. Dan > Radim > >> >> >>>> So now I'm thinking we should retry the write commands when >>>> isPreviousValueNeeded() changes... Not very appealing, but I think the >>>> performance difference is worth it. >>>> >>>>> R. >>>>> >>>>>>> 4) remove write-only commands completely (and probably functional >>>>>>> listeners as well because these will lose their purpose) >>>>>>> >>>>>>> >>>>>>> +1 to remove "unconditional writes", at least an entry version check >>>>>>> should >>>>>>> be applied. >>>>>>> I believe we had already pointed out this would eventually happen, >>>>>>> pretty >>>>>>> much for the reasons you're hitting now. >>>>>>> >>>>>> IMO version checks should be done internally, we shouldn't force the >>>>>> users of the functional API to deal with versions themselves because >>>>>> we know how hard making write skew checks work is for us :) >>>>>> >>>>>> And I wouldn't go as far as to remove the functional listeners, >>>>>> instead I would change them so that read-write listeners are invoked >>>>>> on write-only operations and they force the loading of the previous >>>>>> value. I would also add a way for the regular listeners to say whether >>>>>> they need the previous value or not. >>>>>> >>>>>>> Right now I am inclined towards 4). There could be some internal use >>>>>>> (e.g. multimaps) that could use 1) which is ran without a fancy setup, >>>>>>> though, but it's asking for trouble. >>>>>>> >>>>>>> >>>>>>> I agree! >>>>>>> >>>>>>> Thanks >>>>>>> >>>>>>> >>>>>>> WDYT? >>>>>>> >>>>>>> Radim >>>>>>> >>>>>> Cheers >>>>>> Dan >>>> _______________________________________________ >>>> infinispan-dev mailing list >>>> infinispan-dev@lists.jboss.org >>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev >>> >>> -- >>> Radim Vansa <rva...@redhat.com> >>> JBoss Performance Team >>> >>> _______________________________________________ >>> infinispan-dev mailing list >>> infinispan-dev@lists.jboss.org >>> https://lists.jboss.org/mailman/listinfo/infinispan-dev >> _______________________________________________ >> infinispan-dev mailing list >> infinispan-dev@lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/infinispan-dev > > > -- > Radim Vansa <rva...@redhat.com> > JBoss Performance Team > > _______________________________________________ > infinispan-dev mailing list > infinispan-dev@lists.jboss.org > https://lists.jboss.org/mailman/listinfo/infinispan-dev _______________________________________________ infinispan-dev mailing list infinispan-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev
