Two metrics have the same help value

[wangzhao765]

Describe the bug

https://github.com/cortexproject/cortex/blob/master/pkg/compactor/compactor.go
In line 236 and 240, these 2 metrics have the same help value.
It seems that cortex_compactor_blocks_marked_for_deletion_total means the total number of blocks marked for deletion,
and cortex_compactor_garbage_collected_blocks_total means the total number of blocks deleted after being marked?

[pracucci]

It seems that cortex_compactor_blocks_marked_for_deletion_total means the total number of blocks marked for deletion,
and cortex_compactor_garbage_collected_blocks_total means the total number of blocks deleted after being marked?

Not really. They both count the number of blocks marked for deletion. The number of blocks hard deleted (after being marked) is tracked by cortex_compactor_blocks_cleaned_total.

I think the double metric is somewhat a mistake originated from several iterations on compactor and, from a quick look, I believe we could safely remove cortex_compactor_garbage_collected_blocks_total, but I would need to do a double check.

Help wanted, if anyone wanna take a deeper look and investigate if it's 💯 safe removing cortex_compactor_garbage_collected_blocks_total in favour of cortex_compactor_blocks_marked_for_deletion_total.