Github user yestinchen commented on a diff in the pull request:
https://github.com/apache/flink/pull/4331#discussion_r132348950
--- Diff:
flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
---
@@ -150,6 +160,59 @@ long getWindowTime() {
}
/**
+ * Check pattern after match skip strategy.
+ */
+ private void checkPatternSkipStrategy() {
+ AfterMatchSkipStrategy afterMatchSkipStrategy =
currentPattern.getAfterMatchSkipStrategy();
+ if (afterMatchSkipStrategy.getStrategy() ==
AfterMatchSkipStrategy.SkipStrategy.SKIP_TO_FIRST ||
+ afterMatchSkipStrategy.getStrategy() ==
AfterMatchSkipStrategy.SkipStrategy.SKIP_TO_LAST) {
+ Pattern<T, ?> pattern = currentPattern;
+ while
(!pattern.getName().equals(afterMatchSkipStrategy.getPatternName())) {
+ pattern = pattern.getPrevious();
+ }
+ // pattern name match check.
+ if (pattern == null) {
+ throw new
MalformedPatternException("the pattern name specified in AfterMatchSkipStrategy
" +
+ "can not be found in the given
Pattern");
+ } else {
+ // can not be used with optional states.
+ if
(pattern.getQuantifier().hasProperty(Quantifier.QuantifierProperty.OPTIONAL)) {
+ throw new
MalformedPatternException("the AfterMatchSkipStrategy "
+ +
afterMatchSkipStrategy.getStrategy() + " can not be used with optional
pattern");
+ }
+ }
+
+ // start position check.
+ if (pattern.getPrevious() == null) {
--- End diff --
I agree with you that the fallback approach is much easier to understand
and maintain.
If we discard nothing, the actual sematics is to use SKIP_TO_NEXT_EVENT for
the next match process. But it will have an impact on matching sematics, which
may lead to incorrect results. I think users should be aware of what happens.
My original thought was to add a configuration switch, to let user choose
between throwing exceptions and falling back to a default skip strategy.
Do you have any ideas about that?
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