Understanding access plan evaluation decisions

The topics in this section list typical access plan analysis questions, and areas that you can investigate to increase pushdown opportunities.

Why isn't this predicate being evaluated remotely?
This question arises when a predicate is very selective and thus could be used to filter rows and reduce network traffic. Remote predicate evaluation also affects whether a join between two tables of the same data source can be evaluated remotely.
Why isn't the GROUP BY operator evaluated remotely?
There are several areas that you can check to determine why a GROUP BY operator is not evaluated remotely.
Why isn't the SET operator evaluated remotely?
You can check the operands and check data source restrictions to determine why the SET operator is not evaluated remotely.
Why isn't the ORDER BY operation evaluated remotely?
You can check the input to the operation, what the clause contains, and check data source restrictions to determine why the ORDER BY operator is not evaluated remotely.
Why is a remote INSERT with a fullselect statement not completely evaluated remotely?
You can check several elements of the subselect to determine why a remote INSERT with a fullselect statement is not completely evaluated remotely.
Why is a remote INSERT with VALUES clause statement not completely evaluated remotely?
You can check the VALUES clause and the expression to determine why a remote INSERT with a VALUES clause statement is not completely evaluated remotely.
Why is a remote, searched UPDATE statement not completely evaluated remotely?
You can check elements of the SET clause and search condition to determine why a remote, searched UPDATE statement is not completely evaluated remotely.
Why is a positioned UPDATE statement not completely evaluated remotely?
This happens when the federated database chooses to evaluate the update expression locally before sending the UPDATE statement to the data source. This approach should not significantly affect performance.
Why is a remote, searched DELETE statement not completely evaluated remotely?
You can check elements of the search condition to determine why a remote, searched DELETE statement is not completely evaluated remotely.

Parent topic: Tuning query processing

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