Hi,
Query:
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I am aware of the fact that Expression evaluator is used to filter tuples based on the qual. However, I think it is not the only purpose it serves. As I manipulated the ExecEvalVar in the executor, the queries started behaving abnormally (the comparison operators < , <>, > lost effect and at times started working ). Is the creation of qual also done (in part?) by the expression evaluator? If yes, what part of query creation process is handled by the evaluator? I know ExecInitExpr does expr -> exprstate tree creation, but it is not the evaluator.
If the above is confusing, I just want to ask: "Is expression evaluator, even in part responsible for {PLANNEDSTMT creation?"
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My work / trial so far:
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I see that the target list to be scanned is handled by "ExecTargetList" function.
I am not so sure about this because this function is not listed in the list of functions which GDB shows me (./configure --enable-debug && make clean && make && make install). Rest everything else (almost / perhaps) is shown! (Can anyone tell why? :( )
Whatever be the case, I think the target list creation will somehow call ExecEvalVar because:
1. It is this function whose modification gets me the erroneous behavior.
2. Server, when run in debug 4 / 5 mode shows target entries as VARs.
3. VARs are range table representation in some form and ExecEvalVar makes sense to create the target entry.
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What changes caused this:
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I inserted this line into ExecEvalVar as well as ExecEvalScalarVar:
return cute_datum_array[attnum];
before:
return slot_getattr(slot, attnum, isNull);
It was just an experiment to see how things are getting done. I know most devs here would suggest GDB but I am already using that and I did this to check possible effects than trace.
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I seriously think the target list would involve VARs whose one-time evaluation is done. Since cute_datum_array was a garbage array (intentional), it would crash! Am I right?
Regards,
Vaibhav