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From "Evgeny Kotkov (JIRA)" <>
Subject [jira] [Reopened] (SVN-4658) Can't reconstruct fulltext from DELTA against PLAIN in FSFS
Date Tue, 29 Nov 2016 16:40:58 GMT


Evgeny Kotkov reopened SVN-4658:

(Reopening this issue to adjust Fix Versions)

> Can't reconstruct fulltext from DELTA against PLAIN in FSFS 
> ------------------------------------------------------------
>                 Key: SVN-4658
>                 URL:
>             Project: Subversion
>          Issue Type: Bug
>          Components: libsvn_fs_fs
>    Affects Versions: 1.9.4
>         Environment: All
>            Reporter: Stefan Fuhrmann
>            Assignee: Stefan Fuhrmann
>             Fix For: 1.8.17, 1.9.5, trunk
> A DELTA representation against a PLAIN delta base will not be
> reconstructed correctly if
>   * it spans multiple txdelta windows (100kB), and
>   * there is a match against the base in one window W, and
>   * there has been no match against the base in the previous window W-1,
> because the matching data is being taken from W-1 or earlier instead
> of W.  This causes an MD5 checksum mismatch and the data cannot be
> read.
> In repositories only written to by the Subversion libraries, i.e. no
> third-party code, this issue is virtually restricted to properties and
> directories after enabling their deltification in an existing repository.
> The chances of the problem to actually manifest are small:
>   * Either, there must be node properties > 100kB that changed
>     so much that there is a 100kB that has no 64 byte match
>     with some earlier version of it.  That would basically
>     limit this to non-textual properties.
>   * Or, there must be a directory with several 1000 entries
>     and each of these must have been touched, added or removed
>     over the last 512 revisions (max default delta span).
>     Or there were > 1000 entries added at or removed from the
>     beginning of the directory to shift the delta window
>     sufficiently.
> The data is not being corrupted nor is there a known mechanism to corrupt
> later commits due to this bug.  A workaround is possible by re-instantiating
> the previous version of the node:
>   * svn rm /url/of/unreadable/node
>   * svn cp /url/of/unreadable/node /url/of/unreadable/node@R-1
> or by disabling directory and / or property deltification.

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