helprdiff-backup - Support: sr #105376, geometric series feature


sr #105376: geometric series feature

Submitted by:  Bobby Hesselbo <bhesselbo>
Submitted on:  Tue 30 May 2006 10:50:23 PM UTC  
Votes:  50  
Category:  None Priority:  5 - Normal
Severity:  1 - Wish Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open Operating System:  None

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Sat 25 Jul 2009 06:55:53 PM UTC, comment #4: 

geometrical is not possible in any backup system doing differential incrementals (and I only know rdiff-backup doing this). It's much easier to do in a backup system storing full files for the incrementals.
What is wished and doable is to have a keep philosophy.
A rule idea would be:
Delete all backups older than 1 month except fridays & delete all backups older than 1 year except 1st friday of month.
Result is that you can restore any backup for the last 30 days.
You can also restore backups of fridays for last year (52 backups)
And any backup older than a year done on 1st firday of the month (12 backups/year)


Tue 19 Dec 2006 02:13:17 AM UTC, comment #3: 

I agree that deleting intermediate delta's would be useful and is possible. (It's very easy if you're willing to use a lot of temp space, harder if you want to do it 'correctly'.) However, I believe you can only merge deltas -- moving them along in a non-linear fashion as this post requests seems out of the question.

The thinking I've done on merging deltas correctly currently involves building some skeletal map of the file in memory, and I'm not yet sure if that map will have to completely in memory, or if it could be done in an online method.

Andrew Ferguson <owsla>
Project Administrator
Tue 19 Dec 2006 02:04:32 AM UTC, comment #2: 

sure we could make something like this work... it's actually sort of on the wishlist already -- i forget where ben placed that, but one of the features several of us wanted was the ability to regenerate deltas so as to delete intermediate deltas.  it's all technically possible, but nobody has written the code.

you couldn't really maintain a geometric sequence though because once you'd deleted some of the intermediates you couldn't regenerate them... but you could do various forms of aging.

dean gaudet <dgaudet>
Project Administrator
Mon 18 Dec 2006 10:39:43 PM UTC, comment #1: 

I'm not sure this feature makes sense in the context of rdiff-backup. Here's why:

Let's say on Day N I have my geometric backup. The contents of my archive are:
Day N
Day N-2
Day N-4
Day N-8
Day N-16

Then the next day, Day N+1, I again backup, and again desire my geometric progression. The contents of my archive would be:
Day N+1
Day (N+1)-2 == Day N-1
Day (N+1)-4 == Day N-3
Day (N+1)-8 == Day N-7
Day (N+1)-16 == Day N-15

Since rdiff-backup stores increments of files (ie, diff files), it would be impossible to create Day N-15 from Day N-16 with only Day N-8, etc. We don't have enough information about Day N-15 to reconstruct it.

I believe this kind of setup is simply perpendicular to the design of rdiff-backup, no?

Andrew Ferguson <owsla>
Project Administrator
Tue 30 May 2006 10:50:23 PM UTC, original submission:  

how about having a feature to remove all but a geometric progression of increments, so that one could backup every day and keep days 2, 4, 8, 16 etc. Not possible exactly of course, but can be approximated:

- keep the oldest but remove all increments more than 2/3 as old as the oldest
- repeat with the then next oldest etc

Such a 'remove-geometric' function could be used as often as one felt like (e.g. every backup), to keep the number of increments under control

Maybe there's already an easy way to do this?

Bobby Hesselbo <bhesselbo>


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