borg prune visualized
=====================

Assume it is 2016-01-01, today's backup has not yet been made and you have
created at least one backup on each day in 2015 except on 2015-12-20 (no
backup made on that day).

This is what borg prune --keep-daily 14 --keep-monthly 6 would keep.

Backups kept by the --keep-daily rule are marked by a "d" to the right,
backups kept by the --keep-monthly rule are marked by a "m" to the right.

Calendar view
-------------

                            2015
      January               February               March          
Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  
          1  2  3  4                     1                     1  
 5  6  7  8  9 10 11   2  3  4  5  6  7  8   2  3  4  5  6  7  8  
12 13 14 15 16 17 18   9 10 11 12 13 14 15   9 10 11 12 13 14 15  
19 20 21 22 23 24 25  16 17 18 19 20 21 22  16 17 18 19 20 21 22  
26 27 28 29 30 31     23 24 25 26 27 28     23 24 25 26 27 28 29  
                                            30 31                 

       April                  May                   June          
Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  
       1  2  3  4  5               1  2  3   1  2  3  4  5  6  7  
 6  7  8  9 10 11 12   4  5  6  7  8  9 10   8  9 10 11 12 13 14  
13 14 15 16 17 18 19  11 12 13 14 15 16 17  15 16 17 18 19 20 21  
20 21 22 23 24 25 26  18 19 20 21 22 23 24  22 23 24 25 26 27 28  
27 28 29 30           25 26 27 28 29 30 31  29 30m                
                                                                  

        July                 August              September        
Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  
       1  2  3  4  5                  1  2      1  2  3  4  5  6  
 6  7  8  9 10 11 12   3  4  5  6  7  8  9   7  8  9 10 11 12 13  
13 14 15 16 17 18 19  10 11 12 13 14 15 16  14 15 16 17 18 19 20  
20 21 22 23 24 25 26  17 18 19 20 21 22 23  21 22 23 24 25 26 27  
27 28 29 30 31m       24 25 26 27 28 29 30  28 29 30m             
                      31m                                         

      October               November              December        
Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  
          1  2  3  4                     1      1  2  3  4  5  6  
 5  6  7  8  9 10 11   2  3  4  5  6  7  8   7  8  9 10 11 12 13  
12 13 14 15 16 17 18   9 10 11 12 13 14 15  14 15 16 17d18d19d20  
19 20 21 22 23 24 25  16 17 18 19 20 21 22  21d22d23d24d25d26d27d 
26 27 28 29 30 31m    23 24 25 26 27 28 29  28d29d30d31d           
                      30m                                          

List view
---------

--keep-daily 14     --keep-monthly 6
-------------------------------------------------
 1. 2015-12-31          (2015-12-31 kept by daily rule)
 2. 2015-12-30       1. 2015-11-30
 3. 2015-12-29       2. 2015-10-31
 4. 2015-12-28       3. 2015-09-30
 5. 2015-12-27       4. 2015-08-31
 6. 2015-12-26       5. 2015-07-31
 7. 2015-12-25       6. 2015-06-30
 8. 2015-12-24
 9. 2015-12-23
10. 2015-12-22
11. 2015-12-21
    (no backup made on 2015-12-20)
12. 2015-12-19
13. 2015-12-18
14. 2015-12-17


Notes
-----

2015-12-31 is kept due to the --keep-daily 14 rule (because it is applied
first), not due to the --keep-monthly rule.

Because of that, the --keep-monthly 6 rule keeps Nov, Oct, Sep, Aug, Jul and
Jun. December is not considered for this rule, because that backup was already
kept because of the daily rule.

2015-12-17 is kept to satisfy the --keep-daily 14 rule - because no backup was
made on 2015-12-20. If a backup had been made on that day, it would not keep
the one from 2015-12-17.

We did not include yearly, weekly, hourly, minutely or secondly rules to keep
this example simple. They all work in basically the same way.

The weekly rule is easy to understand roughly, but hard to understand in all
details. If interested, read "ISO 8601:2000 standard week-based year".
