[jira] [Commented] (FLINK-7424) `CEP` component make `KeyedStream` choose wrong channel

["Aljoscha Krettek (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-7424?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16123143#comment-16123143 ] 

Aljoscha Krettek commented on FLINK-7424:
-----------------------------------------

The key returned from a {{KeySelector}} must be deterministic because Flink will call {{getKey()}} whenever it needs the key for a given element. It will not call {{getKey()}} only once and store the result. This is the reason for your second {{KeySelector}} not working.

Unfortunately this is not well documented but there is an issue for fixing that: https://issues.apache.org/jira/browse/FLINK-4047.

> `CEP` component make `KeyedStream` choose wrong channel
> -------------------------------------------------------
>
>                 Key: FLINK-7424
>                 URL: https://issues.apache.org/jira/browse/FLINK-7424
>             Project: Flink
>          Issue Type: Bug
>          Components: CEP, Streaming
>            Reporter: Benedict Jin
>            Assignee: Benedict Jin
>
> `CEP` component make `KeyedStream` choose wrong channel
> Origin KeySelector is perfect right.
> {code:java}
> public static KeySelector<HBaseServerLog, Integer> buildKeySelector() {
>     return (KeySelector<HBaseServerLog, Integer>) log -> {
>         if (log == null) return 0;
>         Integer flumeId;
>         if ((flumeId = log.getFlumeId()) == null) return 1;
>         return flumeId;
>     };
> }
> {code}
> After some changes, it will throw Key group index out of range of key group range [16, 32) exception.
> {code}
> public static KeySelector<HBaseServerLog, Integer> buildKeySelector(final int parallelism) {
>     return new KeySelector<HBaseServerLog, Integer>() {
>         private Random r = new Random(System.nanoTime());
>         @Override
>         public Integer getKey(HBaseServerLog log) throws Exception {
>             if (log == null) return 0;
>             Integer flumeId;
>             if ((flumeId = log.getFlumeId()) == null) return 1;
>             return Math.max(flumeId + (r.nextBoolean() ? 0 : -1 * r.nextInt(parallelism)), 0);
>         }
>     };
> }
> {code}
> But, after MathUtils.murmurHash(keyHash) % maxParallelism process, it shouldn't be wrong. Actually, when we add some `CEP` component (IterativeCondition/PatternFlatSelectFunction) code after it. It make the KeySelector  choose wrong channel and throw IllegalArgumentException.



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