Add Support for --skip-if-unchanged

[fortysix2ahead]

V0.17 introduced the option to skip if there are no changes. It seems that backrest does not have support for that.

To Reproduce Add --skip-if-unchanged to backup options and try to make a snapshot

Expected behavior No snapshot created and no event should be visible.

Screenshots Backrest fails with the following error message:

[restic] command: /bin/restic-0.17.0 snapshots --json -o sftp.args=-oBatchMode=yes --tag plan:playground,created-by:pi5
...
[restic] command: /bin/restic-0.17.0 backup --json /home/playground -o sftp.args=-oBatchMode=yes --exclude-caches --tag plan:playground --tag created-by:pi5 --parent ad9c71eadde1f92dada2388f9da8d461c8502610fc09f23a64d8017d3bd21f20 --host pi5 --skip-if-unchanged
[restic] {"message_type":"summary","files_new":0,"files_changed":0,"files_unmodified":105,"dirs_new":0,"dirs_changed":0,"dirs_unmodified":60,"data_blobs":0,"tree_blobs":0,"data_added":0,"data_added_packed":0,"total_files_processed":105,"total_bytes_processed":1776972,"total_duration":0.016859796}

task "backup for plan \"playground\"" returned error: failed to backup: command "/bin/restic-0.17.0 backup --json /home/playground -o sftp.args=-oBatchMode=yes --exclude-cac..." failed: processing command output: no summary event found
Output:
{"message_type":"summary","files_new":0,"files_changed":0,"files_unmodified":105,"dirs_new":0,"dirs_changed":0,"dirs_unmodified":60,"data_blobs":0,"tree_blobs":0,"data_added":0,"data_added_packed":0,"total_files_processed":105,"total_bytes_processed":1776972,"total_duration":0.016859796}

Platform Info

• ARM64 on Docker
• Backrest Version 1.4.0

[oliver-la]

The flag works almost without issues for me, albeit not as one would expect. Snapshots are still created because restic has a weird handling of absolute and relative paths in combination with the flag. As documented here, backrest would need to change the directory first and use relative paths to backup. That might work for single path snapshots, not with multiple paths - at least it seems it'd be hell to implement.

An alternative might be to provide an extra checkbox "Skip identical snapshots" that does a dry-run of the command first. If the output indicates any changes, backrest would run the backup without the dry-run option. Otherwise it'd skip the backup and maybe also provide a visual indication alongside the dry-run command output.

I'm new to restic and backrest, so I'm just spitballing here. Maybe I'm missing something.

To circle back to your issue: Backrest marks snapshots as failed if no snapshot is created using this flag. Otherwise it works as expected.

[fortysix2ahead]

Yes, I am sure. The backrest header says 1.4.0 and the docker image contains restic 0.17.0, which also says 0.17 when called with --version arg.

[fortysix2ahead]

But you are right, actually it works as expected. It's just confusing, that the failed event appears in the list of backups, pretending it being backup that has failed. Pressing "Clear Error History" button removes those events.

[garethgeorge]

Thanks for the report -- overlooked this when initially scanning the update log :)

Interestingly a summary event is definitely printed -- but Backrest ignores it because it fails validation due to the missing snapshot ID.

This probably needs to be a new boolean flag in plan settings. There's some interesting questions of what this should look like in the UI as well i.e. how should all of the backup operations that don't add snapshots be displayed without cluttering the UI (e.g. should they all be linked to the last created snapshot ID?).

Interested to hear what behaviors people would expect.

[oliver-la]

@garethgeorge In my opinion, a skipped snapshot should not appear in the tree view. Thus, I'm able to quickly see a timeline of changes and in case of a restore, be able to pinpoint the precise snapshot I want to restore. To verify the backups are running as scheduled, a corresponding entry in the operation list should be enough. What do you think?

[fortysix2ahead]

I have a similar feeling. Skipped snapshots should not appear. If have a working folder and you worked on a single document in that folder over the last four weeks it would be easy to see, yes there's a change last Friday, last Tuesday and two weeks ago. You could easily search and restore what you want.

[patrontheo]

would love support for that as well :)

[garethgeorge]

Supported in 1.6.0