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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 05:05:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4499?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16221621#comment-16221621
] 

Richard Yu edited comment on KAFKA-4499 at 10/27/17 5:04 AM:
-------------------------------------------------------------

I have realized that this particular way is flawed and should be reconsidered. There is an
another approach from my understanding, which utilizes provided methods in TreeMap:

Thread Cache is used as a general storage area, and would be used to access specific NamedCaches,
with each CachingWindowStore being assigned one name. ThreadCache has a method defined as
all(String namespace) which could return all keys present in the specified NamedCache. However
that does not neccesarily mean it would be sorted. 

However, we could utilize TreeMap's descendingKeySet() method to get all keys in descending
order. This would require the definition of a new method in NamedCache which calls upon descendingKeySet()
but in effect it will allow us a sorted set from which to operate. 


was (Author: yohan123):
I have realized that this particular way is flawed and should be reconsidered. There is an
another approach from my understanding, which utilizes provided methods in TreeMap:

Thread Cache is used as a general storage area, and would be used to access specific NamedCaches,
with each CachingWindowStore being assigned one name. ThreadCache has a method defined as
all(String namespace) which could return all keys present in the specified NamedCache. However
that does not neccesarily mean it would be sorted. 

However, we could utilize TreeMap's descendingKeySet() method to get all keys in ascending
order. This would require the definition of a new method in NamedCache which calls upon descendingKeySet()
but in effect it will allow us a sorted set from which to operate. 

> 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
>         Attachments: 4499-CachingWindowStore-v1.patch
>
>
> 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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