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https://issues.apache.org/jira/browse/KAFKA-3726?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15295541#comment-15295541
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Radoslaw Gruchalski commented on KAFKA-3726:
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[~benstopford]: This is exactly what I pointed out in the writeup. The case is
not to commit to a certain kind of storage for cold storage and consume the
data. The case is to have an option to take a backup of offset files and
consume them later, when / if necessary. The raw data is already in Kafka in a
most optimal format for re-consumption. Having a backup of offset files frees
the operator from:
- consuming (utilizing resources for consumption) and committing to a certain
storage format
- injecting back to Kafka for re-consumption
The point of this ticket is to discuss an option of a structured, out of the
box method for taking backups of the offset files and not relying on
eventuality of the offset files still being there when the operator wants to
back them up. In other words, it would be great if the deletion of compacted
offset files could be controlled a little bit more allowing operators backing
them up with 100% accuracy.
> Enable cold storage option
> --------------------------
>
> Key: KAFKA-3726
> URL: https://issues.apache.org/jira/browse/KAFKA-3726
> Project: Kafka
> Issue Type: Wish
> Reporter: Radoslaw Gruchalski
> Attachments: kafka-cold-storage.txt
>
>
> This JIRA builds up on the cold storage article I have published on Medium.
> The copy of the article attached here.
> The need for cold storage or an "indefinite" log seems to be quite often
> discussed on the user mailing list.
> The cold storage idea would enable the opportunity for the operator to keep
> the raw Kafka offset files in a third party storage and allow retrieving the
> data back for re-consumption.
> The two possible options for enabling such functionality are, from the
> article:
> First approach: if Kafka provided a notification mechanism and could trigger
> a program when a segment file is to be discarded, it would become feasible to
> provide a standard method of moving data to cold storage in reaction to those
> events. Once the program finishes backing the segments up, it could tell
> Kafka “it is now safe to delete these segments”.
> The second option is to provide an additional value for the
> log.cleanup.policy setting, call it cold-storage. In case of this value,
> Kafka would move the segment files — which otherwise would be deleted — to
> another destination on the server. They can be picked up from there and moved
> to the cold storage.
> Both have their limitations. The former one is simply a mechanism exposed to
> allow operator building up the tooling necessary to enable this. Events could
> be published in a manner similar to Mesos Event Bus
> (https://mesosphere.github.io/marathon/docs/event-bus.html) or Kafka itself
> could provide a control topic on which such info would be published. The
> outcome is, the operator can subscribe to the event bus and get notified
> about, at least, two events:
> - log segment is complete and can be backed up
> - partition leader changed
> These two, together with an option to keep the log segment safe from
> compaction for a certain amount of time, would be sufficient to reliably
> implement cold storage.
> The latter option, {{log.cleanup.policy}} setting would be more complete
> feature but it is also much more difficult to implement. All brokers would
> have keep the backup of the data in the cold storage significantly increasing
> the size requirements, also, the de-duplication of the data for the
> replicated data would be left completely to the operator.
> In any case, the thing to stay away from is having Kafka to deal with the
> physical aspect of moving the data to and back from the cold storage. This is
> not Kafka's task. The intent is to provide a method for reliable cold storage.
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