[GitHub] [geode] albertogpz edited a comment on pull request #6874: GEODE-9602: QueryObserver improvements.

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albertogpz edited a comment on pull request #6874:
URL: https://github.com/apache/geode/pull/6874#issuecomment-934499121


   > Maybe the way to go here is to rewrite `QueryObserverHolder` as a class that hold a `ThreadLocal<QueryObserverHolder>` and then have ALL other product classes such as `DefaultQuery` just use `QueryObserverHolder` as an API for accessing that ThreadLocal.
   
   I like that idea.
   I did an experiment with it but saw many test cases fail:
   https://concourse.apachegeode-ci.info/builds/84932
   
   The problem is that there are test cases that count on setting the observer globally and then running a query from the client. Take a look for example at: `SelectStarQueryDUnitTets::testSelectStarQueryForPartitionedRegion`. In these cases, you cannot set the thread local observer in the thread that will execute the query because the query is executed remotely from the client.
   
   I have been able to change the test cases in `QueryUsingFunctionContextDUnitTest` and set the observer in the function executing the queries instead of globally in the servers but this approach is not valid for the test cases previously mentioned.
   
   I am also worried about the use done by the `QueryObserver` to provide `trace` information in queries. It is not possible to set a query observer and at the same time have trace information.
   
   We could also go for having two variables in the `QueryObserverHolder`: a thread local one and the current global one. Setting the instance could set the value in the global one and getting the instance could check if the thread local has a value. If it does, it would return it. Otherwise, the thread local one would be set to the global one value and then be returned. That way, during a query execution, only the first call to `getInstance()` should require synchronization.
   What do you think?


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