FrankChen021 commented on code in PR #19386:
URL: https://github.com/apache/druid/pull/19386#discussion_r3173283941
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processing/src/main/java/org/apache/druid/math/expr/BuiltInExprMacros.java:
##########
@@ -214,4 +214,95 @@ public Object getLiteralValue()
}
}
+ /**
+ * Expression macro for now() function that returns current system timestamp.
+ * Implemented as a macro to prevent constant folding optimization.
+ */
+ public static class NowExprMacro implements ExprMacroTable.ExprMacro
+ {
+ public static final String NAME = "now";
+
+ @Override
+ public String name()
+ {
+ return NAME;
+ }
+
+ @Override
+ public Expr apply(List<Expr> args)
+ {
+ validationHelperCheckArgumentCount(args, 0);
+ return new NowExpression();
+ }
+
+ static final class NowExpression implements Expr
+ {
+ @Override
+ public ExprEval eval(ObjectBinding bindings)
+ {
+ return ExprEval.ofLong(System.currentTimeMillis());
+ }
+
+ @Override
+ public String stringify()
+ {
+ return "now()";
+ }
+
+ @Override
+ public Expr visit(Shuttle shuttle)
+ {
+ return shuttle.visit(this);
+ }
+
+ @Override
+ public BindingAnalysis analyzeInputs()
+ {
+ // Return analysis indicating this is NOT constant
+ // by pretending we have a free variable
+ return new BindingAnalysis();
Review Comment:
Thanks, this fixes the `ExpressionPlan` constant trait, but I think the
selector path can still fold `now()` once. `NowExpression.analyzeInputs()` now
reports only the synthetic `__dummy__` binding; for normal segments that column
has no capabilities and its selector is nil, so
`ExpressionSelectors.createBindings` drops it and returns
`InputBindings.nilBindings()`. `makeExprEvalSelector` then treats those nil
bindings as a constant expression and returns `new
ConstantExprEvalSelector(plan.getExpression().eval(bindings))`, so `now()` is
still evaluated when the selector is created instead of at row/query processing
time. The new tests cover the planner only; could you add selector-level
coverage and avoid using a missing dummy input as the non-determinism marker?
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