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https://issues.apache.org/jira/browse/KAFKA-4499?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16178466#comment-16178466
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Matthias J. Sax commented on KAFKA-4499:
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First, the description above is just a sketch/place-holder and the actual
design must be done in a KIP. For methods to be added: they should be added to
{{ReadOnlyWindowStore}} ({{WindowStore}} will automatically inherit them of
course -- note, that {{WindowStore}} extends {{ReadOnlyWindowStore}}, but not
the other way round). The actual implementation would be done in
{{RocksDBWindowStore}} and {{CachingWindowStore}} (of course other classes will
be affected, too). It's not a trivial change, if that was your question.
> 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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