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From Branko ─îibej <br...@apache.org>
Subject Re: Backward or forward deltas, backend, FSX
Date Fri, 16 Feb 2018 01:07:38 GMT
On 15.02.2018 22:11, Daniel Shahaf wrote:
>> With say, 100000 revisions, when someone checks out the last revision: 
>> svn starts (would start, with the FSX backend) 
>> with the 30 years old, "fossile" ancient revision? (It would be case 
>> with the "FSFS-like way".) Which has nothing common 
>> with the recent revisions? And applies (at least) 17 deltas (patches)? 
>> Of which many deltas are very "heavy" (huge 
>> changings, complete rewritings)?.. I would marvel at that and do not 
>> understand the reasons..
> Note that when the delta is larger than the file it results in,
> Subversion stores a compressed fulltext rather than a delta.  Your
> example of a file that has undergone multiple complete rewrites might
> exercise that logic, which will shorten the walk.
>
> I'm not sure why you say "at least" 17 deltas.  The default value of
> max-linear-deltification (see fsfs.conf) is 16, meaning that no fulltext
> will require 17 delta applications to produce.

Another important thing to note is that the deltas are not applied in
series; they are _combined_ in series and then the resulting combined
delta is applied to the initial fulltext. Combining deltas is (in
general) lot cheaper than applying them.

-- Brane


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