FrankChen021 commented on code in PR #19386:
URL: https://github.com/apache/druid/pull/19386#discussion_r3189389262
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processing/src/main/java/org/apache/druid/math/expr/BuiltInExprMacros.java:
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@@ -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, the selector constant-folding path I called out is fixed now:
`now()` carries a non-deterministic analysis flag and `ExpressionSelectors`
skips `ConstantExprEvalSelector` for it. I think two related constant/cache
paths still need the same treatment, though. `Expr.asBitmapColumnIndex` still
treats any expression with no required bindings as a constant bitmap index, so
an expression filter around `now()` can still be evaluated once while building
the bitmap. Also, `ExpressionDimFilter` and `ExpressionVirtualColumn` cache
keys still serialize the stable expression cache key (`now()` stringifies the
same way every time), so cached query results can be reused across wall-clock
changes. Could you either make non-deterministic expressions non-cacheable for
these query components, or include a non-stable cache key / disable the
affected optimizations when `analysis.isNonDeterministic()` is true?
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