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https://issues.apache.org/jira/browse/FLINK-7169?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16120936#comment-16120936
]
ASF GitHub Bot commented on FLINK-7169:
---------------------------------------
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?
> Support AFTER MATCH SKIP function in CEP library API
> ----------------------------------------------------
>
> Key: FLINK-7169
> URL: https://issues.apache.org/jira/browse/FLINK-7169
> Project: Flink
> Issue Type: Sub-task
> Components: CEP
> Reporter: Yueting Chen
> Assignee: Yueting Chen
> Fix For: 1.4.0
>
>
> In order to support Oracle's MATCH_RECOGNIZE on top of the CEP library, we
> need to support AFTER MATCH SKIP function in CEP API.
> There're four options in AFTER MATCH SKIP, listed as follows:
> 1. AFTER MATCH SKIP TO NEXT ROW: resume pattern matching at the row after the
> first row of the current match.
> 2. AFTER MATCH SKIP PAST LAST ROW: resume pattern matching at the next row
> after the last row of the current match.
> 3. AFTER MATCH SKIP TO FIST *RPV*: resume pattern matching at the first row
> that is mapped to the row pattern variable RPV.
> 4. AFTER MATCH SKIP TO LAST *RPV*: resume pattern matching at the last row
> that is mapped to the row pattern variable RPV.
> I think we can introduce a new function to `CEP` class, which takes a new
> parameter as AfterMatchSKipStrategy.
> The new API may looks like this
> {code}
> public static <T> PatternStream<T> pattern(DataStream<T> input, Pattern<T, ?>
> pattern, AfterMatchSkipStrategy afterMatchSkipStrategy)
> {code}
> We can also make `SKIP TO NEXT ROW` as the default option, because that's
> what CEP library behaves currently.
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