This adds back ruby_memory_bytes for backwards compatibility, limits
code duplication, cleans up unused methods, and limits the unicorn
worker sampling scope.
This updates monitor docs to reflect the new ruby and unicorn metrics as
well as making it so we fetch process start time via the proc table
instead of via CLOCK_BOOTTIME
On reload, references to Metrics within classes in the Gitlab::Metrics
module fail. Update all references to ::Gitlab::Metrics so that
constant lookup finds the right module in development. This fix should
not impact production.
* Use a simple counter for sampler duration instead of a histogram.
* Use a counter to collect GC time.
* Remove unused objects metric.
* Cleanup metric names to match Prometheus conventions.
* Prefix generic GC stats with `gc_stat`.
* Include worker label on memory and file descriptor metrics.
In MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15834 we
removed use of the data produced by the Allocations Gem. However, we
never removed the code that just enables tracking of allocations. In
this commit we remove all remaining traces of this Gem.
