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From "Matthias J. Sax (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-6249) Interactive query downtime when node goes down even with standby replicas
Date Tue, 28 Nov 2017 16:28:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-6249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16268997#comment-16268997
] 

Matthias J. Sax commented on KAFKA-6249:
----------------------------------------

Thanks. I understand what you are saying. This is related to another issue (basically, your
fail-over behaves the same way as scale-out scenario for which StandbyTasks don't help): KAFKA-6145

Will close this as duplicate.

> Interactive query downtime when node goes down even with standby replicas
> -------------------------------------------------------------------------
>
>                 Key: KAFKA-6249
>                 URL: https://issues.apache.org/jira/browse/KAFKA-6249
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 1.0.0
>            Reporter: Charles Crain
>
> In a multi-node Kafka Streams application that uses interactive queries, the queryable
store will become unavailable (throw InvalidStateStoreException) for up to several minutes
when a node goes down.  This happens regardless of how many nodes are in the application as
well as how many standby replicas are configured.
> My expectation is that if a standby replica is present, that the interactive query would
fail over to the live replica immediately causing negligible downtime for interactive queries.
 Instead, what appears to happen is that the queryable store is down for however long it takes
for the nodes to completely rebalance (this takes a few minutes for a couple GB of total data
in the queryable store's backing topic).
> I am filing this as a bug, realizing that it may in fact be a feature request.  However,
until there is a way we can use interactive queries with minimal (~zero) downtime on node
failure, we are having to entertain other strategies for serving queries (e.g. manually materializing
the topic to an external resilient store such as Cassandra) in order to meet our SLAs.
> If there is a way to minimize the downtime of interactive queries on node failure that
I am missing, I would like to know what it is.
> Our team is super-enthusiastic about Kafka Streams and we're keen to use it for just
about everything!  This is our only major roadblock.



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