[jira] [Created] (FLINK-10831) Consider making processing time monotonically increasing by default

["Andrey Zagrebin (JIRA)" <ji...@apache.org>]

Andrey Zagrebin created FLINK-10831:
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             Summary: Consider making processing time monotonically increasing by default
                 Key: FLINK-10831
                 URL: https://issues.apache.org/jira/browse/FLINK-10831
             Project: Flink
          Issue Type: Improvement
            Reporter: Andrey Zagrebin


At the moment, the processing time is basically implemented in a fixed way as 

System.currentTimeMillis() and not configurable by users.

The timestamp provided this way is not guaranteed to be monotonically increasing. It can jump back for a while because of possible periodic synchronisation of local clock with other more accurate system. It can be a problem for application business logic if we say that the general notion of time is that it always increases.

We can change SystemProcessingTimeService to emit only timestamp which is not less than the latest emitted one, at least for current JVM process.

This change in behaviour can be also configurable if somebody e.g. relies on rather accurate time.
Other option is that if user needs monotonic processing time then custom processing time service should be provided as suggested in FLINK-10830.



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