"borg compact" reports a wrong "freed space" value

[LaurentBonnaud]

Have you checked borgbackup docs, FAQ, and open Github issues?

Yes

Is this a BUG / ISSUE report or a QUESTION?

BUG

System information. For client/server mode post info for both machines.

Intel with 16GB of RAM

Your borg version (borg -V).

1.2.0b2

Operating system (distribution) and version.

Ubuntu 20.10

Hardware / network configuration, and filesystems used.

local repo on btrfs

How much data is handled by borg?

1.1TB

Full borg commandline that lead to the problem (leave away excludes and passwords)

$ borg-1.2b2 -v compact /myrepo
compaction freed about 244.55 MB repository space.

$ borg-1.2b2 -v compact /myrepo
compaction freed about 106.94 MB repository space.

$ borg-1.2b2 -v compact /myrepo
compaction freed about 106.93 MB repository space.

Describe the problem you're observing.

borg compact needs several iterations to reach a final state and does not seem to compact as much as it should. More precisely a lot of 17 bytes files remain after compacttion:

# find /myrepo | wc
 200649  200649 2351093

# find /myrepo -size 17c | wc
  20344   20344  244128

Can you reproduce the problem? If so, describe how. If not, describe troubleshooting steps you took before opening the issue.

I observed the same behavior on several machines/systems/repos.

[ThomasWaldmann]

Interesting, have to investigate...

In general, there is a default --threshold which is not 0, so it won't compact segments with little space to free. But even with that, it should be stable after first iteration.

[ThomasWaldmann]

(borg-env) user@development:~/w/borg$ borg -V
borg 1.2.0b2

(borg-env) user@development:~/w/borg$ borg init -e none repo

(borg-env) user@development:~/w/borg$ borg create repo::arch1 src/
(borg-env) user@development:~/w/borg$ du -sk repo
10704   repo

(borg-env) user@development:~/w/borg$ borg create repo::arch2 /bin 
(borg-env) user@development:~/w/borg$ du -sk repo
17532   repo

(borg-env) user@development:~/w/borg$ borg delete repo::arch1
(borg-env) user@development:~/w/borg$ du -sk repo
17584   repo

(borg-env) user@development:~/w/borg$ borg compact repo
(borg-env) user@development:~/w/borg$ du -sk repo
6896    repo

(borg-env) user@development:~/w/borg$ borg compact repo
(borg-env) user@development:~/w/borg$ du -sk repo
6896    repo

(borg-env) user@development:~/w/borg$ borg delete repo::arch2
(borg-env) user@development:~/w/borg$ du -sk repo
6920    repo

(borg-env) user@development:~/w/borg$ borg compact repo
(borg-env) user@development:~/w/borg$ du -sk repo
80      repo

(borg-env) user@development:~/w/borg$ ls -lR repo/data/
repo/data/:
total 4
drwx------ 2 user user 4096 Feb  8 23:23 0

repo/data/0:
total 8
-rw------- 1 user user 476 Feb  8 23:23 27
-rw------- 1 user user  17 Feb  8 23:23 29

[ThomasWaldmann]

So, for a simple case, it works as expected. Can you write a script that reproduces your issue?

[ThomasWaldmann]

Note: not sure about the amount, but some 17b files are expected with borg 1.2 - commits are intentionally made in separate files.

[LaurentBonnaud]

So, for a simple case, it works as expected.

Your test case is very simple, indeed. There is probably little in common between arch1 and arch2.

Can you write a script that reproduces your issue?

My repo contains full weekly backups of Ubuntu systems (that change a lot) and were started more than 2 years ago.
Generating something similar would not be a trivial task...

btrfs has an interesting util named "btrfs-image". It allows making bug reports about btrfs without making a full copy of a FS by extracting only the internal data structures. A similar tool for borg would be very useful...

[LaurentBonnaud]

In general, there is a default --threshold which is not 0,

I am currently running borg compact --threshold 0 but it takes quite a lot of time.

I will also try the --cleanup-commits option and report back when everything is finished...

[LaurentBonnaud]

(borg-env) user@development:~/w/borg$ borg compact repo

You did not use the -v option.

[ThomasWaldmann]

Can you run the command on your repo again, this time with --debug?

[GeNTooFReaK]

Does compact only works on repos created with 1.2?
I tried 1.2.0b3 compact on a multi-TB repo I created with 1.1 and compact didn't do anything. Tried also with --threshold 0 and --cleanup-commits. I would have expected to reduce at least 300 GB.

Then I created a new repo with 1.2 and put some files into it, deleted some archives and compact correctly cleaned up.