This was attempting to clean up any vectors that no longer have metrics
associated with them. Unfortunately this isn't really possible because
the prometheus client registry allows the second registration of the
same metric, and then throws an error when gathering the metrics.
Another options would be to unregister the metric with the client
library, but that's not implemented for unchecked collectors.
Unfortunately this means that if we have a lot of metrics with differing
label sets appearing and disappearing, that we'll leak some amount of
memory for vectors that are never used again, but this is the way the
old metric tracking code worked also.
Signed-off-by: Clayton O'Neill <claytono@github.com>
This reworks/rewrites the way that metric registration and tracking is
handled across all of statsd_exporter. The goal here is to reduce
memory and cpu usage, but also to reduce complexity by unifying metric
registration with the ttl tracking for expiration.
Some high level notes:
* Previously metric names and labels were being hashed three times for
every event accepted: in the container code, the save label set code and
again in the prometheus client libraries. This unifies the first two
and caches the results of `GetMetricWith` to avoid the third.
* This optimizes the label hashing to reduce cpu overhead and memory
allocations. The label hashing code previously showed up high on all
profiling done for both CPU and memory allocations
Using the BenchmarkExporterListener benchmark, the improvement looks
like this.
Before:
cpu: 11,341,797 ns/op
memory allocated: 1,731,119 B/op
memory allocations: 58,028 allocs/op
After:
cpu: 7,084,651 ns/op
memory allocated: 906,556 B/op
memory allocations: 42,026 allocs/op
Signed-off-by: Clayton O'Neill <claytono@github.com>
