This PR adds support for limiting the maximum shares allocated to a
compaction scheduling class by the compaction controller. It introduces
a new configuration parameter, compaction_max_shares, which, when set
to a non zero value, will cap the shares allocated to compaction jobs.
This PR also exposes the shares computed by the compaction controller
via metrics, for observability purposes.
Fixes https://github.com/scylladb/scylladb/issues/9431
Enhancement. No need to backport.
NOTE: Replaces PR https://github.com/scylladb/scylladb/pull/26696
Ran a test in which the backlog raised the need for max shares (normalized backlog above normalization_factor), and played with different values for new option compaction_max_shares to see it works (500, 1000, 2000, 250, 50)
Closesscylladb/scylladb#27024
* github.com:scylladb/scylladb:
db/config: introduce new config parameter `compaction_max_shares`
compaction_manager:config: introduce max_shares
compaction_controller: add configurable maximum shares
compaction_controller: introduce `set_max_shares()`
384bffb8da