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From "Richard Yu (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (KAFKA-4499) Add "getAllKeys" API for querying windowed KTable stores
Date Fri, 27 Oct 2017 01:39:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4499?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16221561#comment-16221561
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Richard Yu edited comment on KAFKA-4499 at 10/27/17 1:38 AM:
-------------------------------------------------------------

I just like to seek confirmation on something: from my understanding, the fetch() methods
found in ReadOnlyWindowStore, the keys must be sorted when returned. Does that neccesarily
have to be the case with the new methods as well? If so, is it pre or post serialization?



was (Author: yohan123):
I just like to seek confirmation on something: for the fetch() methods found in ReadOnlyWindowStore,
the keys must be sorted when returned. Does that neccesarily have to be the case with the
new methods as well?


> Add "getAllKeys" API for querying windowed KTable stores
> --------------------------------------------------------
>
>                 Key: KAFKA-4499
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4499
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Matthias J. Sax
>              Labels: needs-kip
>
> Currently, both {{KTable}} and windowed-{{KTable}} stores can be queried via IQ feature.
While {{ReadOnlyKeyValueStore}} (for {{KTable}} stores) provide method {{all()}} to scan the
whole store (ie, returns an iterator over all stored key-value pairs), there is no similar
API for {{ReadOnlyWindowStore}} (for windowed-{{KTable}} stores).
> This limits the usage of a windowed store, because the user needs to know what keys are
stored in order the query it. It would be useful to provide possible APIs like this (only
a rough sketch):
>  - {{keys()}} returns all keys available in the store (maybe together with available
time ranges)
>  - {{all(long timeFrom, long timeTo)}} that returns all window for a specific time range
>  - {{allLatest()}} that returns the latest window for each key
> Because this feature would require to scan multiple segments (ie, RockDB instances) it
would be quite inefficient with current store design. Thus, this feature also required to
redesign the underlying window store itself.
> Because this is a major change, a KIP (https://cwiki.apache.org/confluence/display/KAFKA/Kafka+Improvement+Proposals)
is required. The KIP should cover the actual API design as well as the store refactoring.



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