[jira] [Commented] (OAK-2527) Update SegmentMK header format definition

["Michael Dürig (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-2527?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14322952#comment-14322952 ] 

Michael Dürig commented on OAK-2527:
------------------------------------

Committed a fix in trunk at http://svn.apache.org/r1660154. This shouldn't have any impact as the header format stays the same, only its interpretation changed. 

[~alex.parvulescu], would you know about other places in the code where the header format is hard coded and where we'd need to change it? Other wise I'd go forward and merge these changes to the 1.0 branch so we get OAK-2294 unblocked. 

> Update SegmentMK header format definition
> -----------------------------------------
>
>                 Key: OAK-2527
>                 URL: https://issues.apache.org/jira/browse/OAK-2527
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segmentmk
>            Reporter: Michael Dürig
>            Assignee: Michael Dürig
>             Fix For: 1.0.12, 1.1.8
>
>
> Even though the Oak's [segment header format | http://jackrabbit.apache.org/oak/docs/nodestore/segmentmk.html] defines a version, that version is not checked when running Oak. In effect this means current Oak versions pretend to be infinitely forward compatible. 
> To prevent older versions of Oak to run with incompatible, newer storage formats we need to devise a way for Oak to fail fast in that scenario. 
> One thing we could do to introduce versions checking retroactively is to redefine the segment header format from:
> {noformat}
> +--------+--------+--------+--------+--------+--------+--------+--------+
> | magic bytes: "0aK\n" in ASCII     |version |idcount |rootcount        |
> +--------+--------+--------+--------+--------+--------+--------+--------+
> {noformat}
> to: 
> {noformat}
> +--------+--------+--------+--------+--------+--------+--------+--------+
> | magic bytes: "0aK" ASCII |version |reserved|idcount |rootcount        |
> +--------+--------+--------+--------+--------+--------+--------+--------+
> {noformat}
> where version would be {{10}} for the current storage format and {{11}} for the next storage format. 



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