This patch extends the libmetrics logging setup functionality with a
`tracing` layer that increments a Prometheus counter each time we log a
log message. We have the counter per tracing event level. This allows
for monitoring WARN and ERR log volume without parsing the log. Also, it
would allow cross-checking whether logs got dropped on the way into
Loki.
It would be nicer if we could hook deeper into the tracing logging
layer, to avoid evaluating the filter twice.
But I don't know how to do it.
Before this patch, if a tenant would override its eviction_policy
setting to use a lower LayerAccessThreshold::threshold than the
`evictions_low_residence_duration_metric_threshold`, the evictions done
for that tenant would count towards the
`evictions_with_low_residence_duration` metric.
That metric is used to identify pre-mature evictions, commonly triggered
by disk-usage-based eviction under disk pressure.
We don't want that to happen for the legitimate evictions of the tenant
that overrides its eviction_policy.
So, this patch
- moves the setting into TenantConf
- adds test coverage
- updates the staging & prod yamls
Forward Compatibility:
Software before this patch will ignore the new tenant conf field and use
the global one instead.
So we can roll back safely.
Backward Compatibility:
Parsing old configs with software as of this patch will fail in
`PageServerConf::parse_and_validate` with error
`unrecognized pageserver option 'evictions_low_residence_duration_metric_threshold'`
if the option is still present in the global section.
We deal with this by updating the configs in Ansible.
fixes https://github.com/neondatabase/neon/issues/3940
