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https://issues.apache.org/jira/browse/KAFKA-4113?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16937950#comment-16937950
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Matthias J. Sax commented on KAFKA-4113:
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Not sure If I understand. Let's do an example (only showing timestamps,
consuming from left (small offset) to right).
Table-topic-ts: 10, 12, 14, 16, 17, 19, 20
Stream-Topic:ts: 18, 19, 20, 21, 23
Assuming auto.offset.reset=earliest, we would compare the timestamps for both
topic (on a per partition basis, ie, stream-p0 compare to table-p0 etc). In our
example, the table records have the smallest timestamps and would be processed
first, hence, the table would be "bootstraped" from 10 to 17. Afterwards,
stream record with timestamp 18 would be processed because the next table
update has larger timestamp 19.
If the records from both inputs have the same timestamp, there is currently no
guarantee which record is processed first – it's a know gap that we need to
address at some point.
Does this answer your question?
> Allow KTable bootstrap
> ----------------------
>
> Key: KAFKA-4113
> URL: https://issues.apache.org/jira/browse/KAFKA-4113
> Project: Kafka
> Issue Type: New Feature
> Components: streams
> Reporter: Matthias J. Sax
> Assignee: Guozhang Wang
> Priority: Major
>
> 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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