Matthias J. Sax created KAFKA-4113:
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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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