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From Michael Dürig (JIRA) <j...@apache.org>
Subject [jira] [Updated] (OAK-4649) Move index files outside of the TAR files
Date Wed, 09 Nov 2016 08:50:58 GMT

     [ https://issues.apache.org/jira/browse/OAK-4649?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael Dürig updated OAK-4649:
-------------------------------
    Labels: technical_debt  (was: )

> Move index files outside of the TAR files
> -----------------------------------------
>
>                 Key: OAK-4649
>                 URL: https://issues.apache.org/jira/browse/OAK-4649
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segment-tar
>            Reporter: Francesco Mari
>            Assignee: Francesco Mari
>              Labels: technical_debt
>
> TAR files currently embed three indexes: an index of the segments contained in the TAR
files, a graph index and an index of external binary references.
> Index files are checked for consistency purposes at the startup of the system. Normally,
if an index file is corrupted it is recreated. Since the index file is contained inside the
TAR file, recreating them implies rewriting the whole TAR file and appending the new index.

> This process creates unnecessary backups, since the biggest part of the TAR file is effectively
immutable. Moreover, because index files are stored in the TAR files, we can't treat TAR files
as true read-only files. There is always the possibility that they have to be opened again
in write mode for the recovery of the index file.
> I propose to move those index files outside of the TAR files. TAR files will end up being
truly read-only files containing immutable data, and index files will be granted their own
physical files on the file system. Being index files derived data, they now can be recreated
at will without impacting the read-only part of the segment store.



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