zfs mountpoints performance drops inside firejail sandbox

[osevan]

I have a database sandbox for my test and benchmarking.
When i make sysbench read oltp benchmark to my database ontop ext4 filesystem my performance drops from 71k-without Sandbox -, to 60k - inside firejail sandbox.

When i make same benchmark on zfs mountpoint, my performance drops from 92k -without sandbox -, to 39k -inside firejail.

Performance drop of more than 50% inside firejail.

I know , this bug isnt related with security, but developer could test this inside test environment and try to figure out, why on zfs mountpoint huge performance drops existing.

Thanks and
Best regards