Re: [infinispan-dev] Transactional consistency of query
On 07/28/2017 02:59 PM, Adrian Nistor wrote: > My feeling regarding this was to accept such inconsistencies, but > maybe I'm wrong. I've always regarded indexing as being async in > general, even though it did behave as if being sync in some not so > rare circumstances, which probably made people believe it is expected > to be sync in general. I'm curious what Sanne and Gustavo have in mind. > > Please note that updating the index synchronously during tx commit was > always regarded as a performance bottleneck, so it was out of the > question. And that would not always work anyway, it all depends on the > underlying indexing technology. For example when using HS with elastic > search you have to accept that elastic indexing is always async. OK, queries being inherently async would be acceptable for me (as long as we document it - preferably blogging about the limitations, too). Could you make sure that But async should mean that the result looks as being done at some point earlier, maybe mix ordering a bit, but not that it's inconsistent (e.g. returning entries that not match the criteria). Also in case that we store fields in index and return a projection, those values should not come expose any non-committed data. I guess that expecting query in transaction to reflect uncommitted state would be probably too much :) > > And there might not be an index at all. It's very possible that the > query runs unindexed. In that case it will use distributed streams > which have their own transaction issues. Yes; please leave non-indexed queries aside from this discussion. > > In the past we had some bugs were a matching entry was deleted/evicted > right before the search results were returned to the user, so loading > of those values failed in a silent way. Those queries mistakenly > returned some unexpected nulls among other valid results. The fix was > to just filter out those nulls. We could enhance that to double check > that the returned entry is indeed of the requested type, to also cover > the issue that you encountered. It's not just entity type, criteria may be invalidated by any field change. Would a full criteria check on the returned entities be too expensive? Can you even check e.g. native queries against provided set of objects? Radim > > Adrian > > On 07/28/2017 01:38 PM, Radim Vansa wrote: >> Hi, >> >> while working on ISPN-7806 I am wondering how should queries work with >> transactions. Right now it seems that updates to index are done during >> either regular command execution (on originator [A]) or prepare command >> on remote nodes [B]. Both of these cause rolled-back transactions to be >> seen, so these must be treated as bugs [C]. >> >> If we index the data after committing the transaction, there would be a >> time window when we could see the updated entries but the index would >> not reflect that. That might be acceptable limitation if a >> query-matching misses some entity, but it's also possible that we >> retrieve the query result key-set and then (after retrieving full >> entities) we return something that does not match the query. One of the >> reproducers for ISPN-7806 I've written [1] triggers a situation where >> listing all Persons could return Animal (different entity type), so I >> think that there's no validity post-check (though these reproducers >> don't use transactions). >> >> Therefore, I wonder if the index should contain only the key; maybe we >> should store an unique version and invalidate the query if some of the >> entries has changed. >> >> If we index the data before committing the transaction, similar >> situation could happen: the index will return keys for entities that >> will match in the future but the actually returned list will contain >> stale entities. >> >> What's the overall plan? Do we just accept inconsistencies? In that >> case, please add a verbose statement in docs and point me to that. >> >> And if I've misinterpreted something and raised the red flag in error, >> please let me know. >> >> Radim >> >> [A] This seems to be a regression after moving towards async >> interceptors - our impl of >> org.hibernate.search.backend.TransactionContext is incorrectly bound to >> TransactionManager. Then we seem to be running out of transaction and >> are happy to index it right away. The thread that executes the >> interceptor handler is also dependent on ownership (due to remote >> LockCommand execution), so I think that it does not fail the local-mode >> tests. >> >> [B] ... and it does so twice as a regression after ISPN-7840 but that's >> easy to fix. >> >> [C] Indexing in prepare command was OK before ISPN-7840 with pessimistic >> locking which does not send the CommitCommand, but now that the QI has >> been moved below EWI it means that we're indexing before storing the >> actual values. Optimistic locking was not correct, though. >> >> [1] >> https://github.com/rvansa/infinispan/commit/1d62c9b84888c7ac21a9811213b5657aa44
Re: [infinispan-dev] Transactional consistency of query
My feeling regarding this was to accept such inconsistencies, but maybe I'm wrong. I've always regarded indexing as being async in general, even though it did behave as if being sync in some not so rare circumstances, which probably made people believe it is expected to be sync in general. I'm curious what Sanne and Gustavo have in mind. Please note that updating the index synchronously during tx commit was always regarded as a performance bottleneck, so it was out of the question. And that would not always work anyway, it all depends on the underlying indexing technology. For example when using HS with elastic search you have to accept that elastic indexing is always async. And there might not be an index at all. It's very possible that the query runs unindexed. In that case it will use distributed streams which have their own transaction issues. In the past we had some bugs were a matching entry was deleted/evicted right before the search results were returned to the user, so loading of those values failed in a silent way. Those queries mistakenly returned some unexpected nulls among other valid results. The fix was to just filter out those nulls. We could enhance that to double check that the returned entry is indeed of the requested type, to also cover the issue that you encountered. Adrian On 07/28/2017 01:38 PM, Radim Vansa wrote: > Hi, > > while working on ISPN-7806 I am wondering how should queries work with > transactions. Right now it seems that updates to index are done during > either regular command execution (on originator [A]) or prepare command > on remote nodes [B]. Both of these cause rolled-back transactions to be > seen, so these must be treated as bugs [C]. > > If we index the data after committing the transaction, there would be a > time window when we could see the updated entries but the index would > not reflect that. That might be acceptable limitation if a > query-matching misses some entity, but it's also possible that we > retrieve the query result key-set and then (after retrieving full > entities) we return something that does not match the query. One of the > reproducers for ISPN-7806 I've written [1] triggers a situation where > listing all Persons could return Animal (different entity type), so I > think that there's no validity post-check (though these reproducers > don't use transactions). > > Therefore, I wonder if the index should contain only the key; maybe we > should store an unique version and invalidate the query if some of the > entries has changed. > > If we index the data before committing the transaction, similar > situation could happen: the index will return keys for entities that > will match in the future but the actually returned list will contain > stale entities. > > What's the overall plan? Do we just accept inconsistencies? In that > case, please add a verbose statement in docs and point me to that. > > And if I've misinterpreted something and raised the red flag in error, > please let me know. > > Radim > > [A] This seems to be a regression after moving towards async > interceptors - our impl of > org.hibernate.search.backend.TransactionContext is incorrectly bound to > TransactionManager. Then we seem to be running out of transaction and > are happy to index it right away. The thread that executes the > interceptor handler is also dependent on ownership (due to remote > LockCommand execution), so I think that it does not fail the local-mode > tests. > > [B] ... and it does so twice as a regression after ISPN-7840 but that's > easy to fix. > > [C] Indexing in prepare command was OK before ISPN-7840 with pessimistic > locking which does not send the CommitCommand, but now that the QI has > been moved below EWI it means that we're indexing before storing the > actual values. Optimistic locking was not correct, though. > > [1] > https://github.com/rvansa/infinispan/commit/1d62c9b84888c7ac21a9811213b5657aa44ff546 > > ___ infinispan-dev mailing list infinispan-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev
[infinispan-dev] Transactional consistency of query
Hi, while working on ISPN-7806 I am wondering how should queries work with transactions. Right now it seems that updates to index are done during either regular command execution (on originator [A]) or prepare command on remote nodes [B]. Both of these cause rolled-back transactions to be seen, so these must be treated as bugs [C]. If we index the data after committing the transaction, there would be a time window when we could see the updated entries but the index would not reflect that. That might be acceptable limitation if a query-matching misses some entity, but it's also possible that we retrieve the query result key-set and then (after retrieving full entities) we return something that does not match the query. One of the reproducers for ISPN-7806 I've written [1] triggers a situation where listing all Persons could return Animal (different entity type), so I think that there's no validity post-check (though these reproducers don't use transactions). Therefore, I wonder if the index should contain only the key; maybe we should store an unique version and invalidate the query if some of the entries has changed. If we index the data before committing the transaction, similar situation could happen: the index will return keys for entities that will match in the future but the actually returned list will contain stale entities. What's the overall plan? Do we just accept inconsistencies? In that case, please add a verbose statement in docs and point me to that. And if I've misinterpreted something and raised the red flag in error, please let me know. Radim [A] This seems to be a regression after moving towards async interceptors - our impl of org.hibernate.search.backend.TransactionContext is incorrectly bound to TransactionManager. Then we seem to be running out of transaction and are happy to index it right away. The thread that executes the interceptor handler is also dependent on ownership (due to remote LockCommand execution), so I think that it does not fail the local-mode tests. [B] ... and it does so twice as a regression after ISPN-7840 but that's easy to fix. [C] Indexing in prepare command was OK before ISPN-7840 with pessimistic locking which does not send the CommitCommand, but now that the QI has been moved below EWI it means that we're indexing before storing the actual values. Optimistic locking was not correct, though. [1] https://github.com/rvansa/infinispan/commit/1d62c9b84888c7ac21a9811213b5657aa44ff546 -- Radim Vansa JBoss Performance Team ___ infinispan-dev mailing list infinispan-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev
