Compressing local backups

[IdahoPL]

Can I compress (tar.bz2) local backups directories, and delete it (using rm) after compression, to save disk space? Of course for restore I'd uncompress it to original state for recovery. Will it work?

[Slach]

It have no sense.

Local backup is just a hard-links to exist data files, so it doesn't allocate disk space, until original files not deleted (during background merges for example)

And whole clickhouse data already compressed by LZ4 or ZSTD, so additional compression also have no sense in modern version of clickhouse-server

[IdahoPL]

I'm using Bacula to back up this server. Clickhouse directory is excluded, as it's pointless to backup files from running database. I'm backing up with Bacula backups created by clickhouse-backup. So in my case backup data is allocating disk space (in Bacula's backup).

As for compression - single clickhouse-backup backup (directory) is 21 GB. After compression (tar.bz2) it drops to 12 GB. It's 43% or, if you look for a month, 630 GB vs 360 GB.

Anyway - can I safely compress and remove backups made by clickhouse-backup or should I not do it for some reason?

[Slach]

Yes you can safely compress and remove /var/lib/clickhouse/backup/backup_name.
About current compression Which clickhouse-sever version do you use?
Do you have *.cmrk* files in your backup files? or just *.mrk*?

[IdahoPL]

Thank you. I'm using clickhouse-server 25.3.3.42. Only *.cmrk2 and *.cmrk3 files are in backup, no *.mrk*.

[Slach]

in this case, really weird how you achieve x2 compression to already compressed data

[IdahoPL]

Hard to tell why. As far as I could tell data in CH is in fact compressed but still it looks like that:

# clickhouse-backup list 2>/dev/null | grep 2025-07-05T21-00-01
clickhouse-backup_2025-07-05T21-00-01   05/07/2025 21:00:14   local      all:20.78GiB,data:20.78GiB,arch:0B,obj:58.77KiB,meta:0B,rbac:2.04KiB,conf:0B   embedded

# du -sh clickhouse-backup_2025-07-05T21-00-01
21G     clickhouse-backup_2025-07-05T21-00-01

# tar cjpf clickhouse-backup_2025-07-05T21-00-01.tbz2 clickhouse-backup_2025-07-05T21-00-01 && ls -lh clickhouse-backup_2025-07-05T21-00-01.tbz2
-rw-r--r-- 1 root root 12G Jul  6 17:38 clickhouse-backup_2025-07-05T21-00-01.tbz2