Fix backward compatible issue in DistinctCountThetaSketchAggregationFunction

[jackjlli]

This PR fixes a backward incompatible issue introduced by this PR: #12042

Printed stacktrace from the broker log:

Caused by: java.lang.ClassCastException: class org.apache.datasketches.theta.DirectCompactSketch cannot be cast to class org.apache.pinot.segment.local.customobject.ThetaSketchAccumulator (org.apache.datasketches.theta.DirectCompactSketch and org.apache.pinot.segment.local.customobject.ThetaSketchAccumulator are in unnamed module of loader org.eclipse.jetty.webapp.WebAppClassLoader @3b2f4a93)
        at org.apache.pinot.core.query.aggregation.function.DistinctCountThetaSketchAggregationFunction.extractFinalResult(DistinctCountThetaSketchAggregationFunction.java:1019) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.query.aggregation.function.DistinctCountThetaSketchAggregationFunction.extractFinalResult(DistinctCountThetaSketchAggregationFunction.java:82) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.data.table.TableResizer$AggregationFunctionExtractor.extract(TableResizer.java:446) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.data.table.TableResizer.getIntermediateRecord(TableResizer.java:169) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.data.table.TableResizer.getSortedTopRecords(TableResizer.java:280) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.data.table.TableResizer.getTopRecords(TableResizer.java:266) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.data.table.IndexedTable.finish(IndexedTable.java:151) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.data.table.Table.finish(Table.java:59) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.query.reduce.GroupByDataTableReducer.getIndexedTable(GroupByDataTableReducer.java:386) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.query.reduce.GroupByDataTableReducer.reduceWithIntermediateResult(GroupByDataTableReducer.java:146) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.query.reduce.GroupByDataTableReducer.reduceAndSetResults(GroupByDataTableReducer.java:114) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.core.query.reduce.BrokerReduceService.reduceOnDataTable(BrokerReduceService.java:158) ~[org.apache.pinot.pinot-core.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.broker.requesthandler.SingleConnectionBrokerRequestHandler.processBrokerRequest(SingleConnectionBrokerRequestHandler.java:150) ~[org.apache.pinot.pinot-broker.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.broker.requesthandler.BaseBrokerRequestHandler.handleRequest(BaseBrokerRequestHandler.java:766) ~[org.apache.pinot.pinot-broker.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.broker.requesthandler.BaseBrokerRequestHandler.handleRequest(BaseBrokerRequestHandler.java:282) ~[org.apache.pinot.pinot-broker.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.broker.requesthandler.BrokerRequestHandlerDelegate.handleRequest(BrokerRequestHandlerDelegate.java:107) ~[org.apache.pinot.pinot-broker.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]
        at org.apache.pinot.broker.requesthandler.BrokerRequestHandler.handleRequest(BrokerRequestHandler.java:48) ~[org.apache.pinot.pinot-broker.jar:1.1.0e54888f597105216666ee3b0f4d28596434e9652]

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (17db0fd) 61.69% compared to head (db75e44) 61.76%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #12347      +/-   ##
============================================
+ Coverage     61.69%   61.76%   +0.06%     
- Complexity      207     1152     +945     
============================================
  Files          2424     2424              
  Lines        132340   132498     +158     
  Branches      20436    20479      +43     
============================================
+ Hits          81651    81834     +183     
+ Misses        44693    44657      -36     
- Partials       5996     6007      +11     

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unittests2	27.72% <0.00%> (+0.09%)	⬆️

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[vvivekiyer]

Can we please test this if this indeeds helps?

As discussed offline, as a result of the aggregationFunction.merge() step, all Sketch objects should be converted to ThetaSketchAccumulator. So can you clarify why we saw this?

[jackjlli]

Good question! It could be possible that there is only 1 old server returning a non-empty intermediate result, which skipped the merge step in broker.

I've tested this code by setting up a local cluster and running 2 servers with old version and 1 broker with new version, and I don't see exception any more. So we should be good with this hotfix PR.