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From "Matthias J. Sax (JIRA)" <j...@apache.org>
Subject [jira] [Created] (KAFKA-4113) Allow KTable bootstrap
Date Thu, 01 Sep 2016 18:42:20 GMT
Matthias J. Sax created KAFKA-4113:
--------------------------------------

             Summary: Allow KTable bootstrap
                 Key: KAFKA-4113
                 URL: https://issues.apache.org/jira/browse/KAFKA-4113
             Project: Kafka
          Issue Type: Sub-task
          Components: streams
            Reporter: Matthias J. Sax
            Assignee: Guozhang Wang


On the mailing list, there are multiple request about the possibility to "fully populate"
a KTable before actual stream processing start.

Even if it is somewhat difficult to define, when the initial populating phase should end,
there are multiple possibilities:

The main idea is, that there is a rarely updated topic that contains the data. Only after
this topic got read completely and the KTable is ready, the application should start processing.
This would indicate, that on startup, the current partition sizes must be fetched and stored,
and after KTable got populated up to those offsets, stream processing can start.

Other discussed ideas are:
1) an initial fixed time period for populating
(it might be hard for a user to estimate the correct value)
2) an "idle" period, ie, if no update to a KTable for a certain time is
done, we consider it as populated
3) a timestamp cut off point, ie, all records with an older timestamp
belong to the initial populating phase

The API change is not decided yet, and the API desing is part of this JIRA.

One suggestion (for option (4)) was:
{noformat}
KTable table = builder.table("topic", 1000); // populate the table without reading any other
topics until see one record with timestamp 1000.
{noformat}



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