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Posted to oak-issues@jackrabbit.apache.org by "Axel Hanikel (Jira)" <ji...@apache.org> on 2020/06/29 13:37:00 UTC
[jira] [Updated] (OAK-7932) A distributed node store for the cloud
[ https://issues.apache.org/jira/browse/OAK-7932?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Axel Hanikel updated OAK-7932:
------------------------------
Summary: A distributed node store for the cloud (was: A distributed segment store for the cloud)
> A distributed node store for the cloud
> --------------------------------------
>
> Key: OAK-7932
> URL: https://issues.apache.org/jira/browse/OAK-7932
> Project: Jackrabbit Oak
> Issue Type: Wish
> Components: segment-tar
> Reporter: Axel Hanikel
> Assignee: Axel Hanikel
> Priority: Minor
>
> h1. Outline
> This issue documents some proof-of-concept work for adapting the segment tar nodestore to a
> distributed environment. The main idea is to adopt an actor-like model, meaning:
> - Communication between actors (services) is done exclusively via messages.
> - An actor (which could also be a thread) processes one message at a time, avoiding sharing
> state with other actors as far as possible.
> - Segments are kept in RAM and are written to external storage lazily only for disaster recovery.
> - As RAM is a very limited resource, different actors own their share of the total segment space.
> - An actor can also cache a few segments which it does not own but which it uses often (such as
> the one containing the root node)
> - The granularity of operating on whole segments may be too coarse, so perhaps reducing the segment
> size would improve performance.
> - We could even use the segment solely as an addressing component and operate at the record level.
> That would avoid copying data around when collecting garbage: garbage records would just be
> evicted from RAM.
> h1. Implementation
> The first idea was to use ZeroMQ for communication because it seems to be a high-quality and
> easy to use implementation. A major drawback is that the library is written in C and the Java
> library which does the JNI stuff seems hard to set up and did not work for me. There is a native
> Java implementation of the ZeroMQ protocol, aptly called jeromq, which seems to work well so far,
> but I don't know about its performance yet.
> A second implementation, at [https://github.com/ahanikel/jackrabbit-oak/tree/zeromq-nodestore] is a simple
> nodestore implementation which is kind of a dual to the segment store in the sense that it is on the other end
> of the compactness spectrum. The segment store is very dense and avoids duplication whereever possible.
> The nodestore in this implementation, however, is quite redundant: Every nodestate gets its own UUID (a hash of the serialised
> nodestate) and is saved together with its properties, similar to the document node store.
> This redundancy wastes space, but on the other hand garbage
> collection (yet unimplemented) is easier because there is no segment that needs to be rewritten to get rid of data that is no
> longer referenced; unreferenced nodes can just be deleted. This implementation still has bugs, but being much simpler
> than the segment store, it can eventually be used to experiment with different configurations and examine their
> performance.
>
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