GeoIpCache and EnrichCache improvements

[szybia]

• AtomicLong -> LongAdder
  • we largely write stats and read very infrequently, so let's avoid any lock-contention possibilities
  • adding hits_misses_in_millis into DLS cache, and think LongAdder is the better class to use, so changing this to be consistent
• call System::nanoTime twice to measure cache miss times, rather than four times

[elasticsearchmachine]

Pinging @elastic/es-security (Team:Security)

[elasticsearchmachine]

Hi @szybia, I've created a changelog YAML for you.

[joegallo]

There's more prior art (not a ton, but some) for using a CounterMetric for tracking times in the Elasticsearch codebase than for using a LongAdder directly.

joegallo@simulacron:~/Code/elastic/elasticsearch $ git grep 'new LongAdder' | grep -i time | grep -i -E '(nanos|millis)' | grep -iv test/
x-pack/plugin/searchable-snapshots/src/main/java/org/elasticsearch/xpack/searchablesnapshots/store/input/DirectBlobContainerIndexInput.java:            private final LongAdder timeNanos = new LongAdder();
joegallo@simulacron:~/Code/elastic/elasticsearch $ git grep 'new CounterMetric()' | grep -i time | grep -i -E '(nanos|millis)' | grep -iv test/
server/src/main/java/org/elasticsearch/index/engine/Engine.java:        private final CounterMetric throttleTimeMillisMetric = new CounterMetric();
server/src/main/java/org/elasticsearch/ingest/IngestMetric.java:    private final CounterMetric ingestTimeInNanos = new CounterMetric();
server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreSnapshotMetrics.java:    private final CounterMetric snapshotRateLimitingTimeInNanos = new CounterMetric();
server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreSnapshotMetrics.java:    private final CounterMetric restoreRateLimitingTimeInNanos = new CounterMetric();
server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreSnapshotMetrics.java:    private final CounterMetric uploadTimeInMillis = new CounterMetric();
server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreSnapshotMetrics.java:    private final CounterMetric uploadReadTimeInNanos = new CounterMetric();
x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportGetTrainedModelsStatsAction.java:        CounterMetric ingestTimeInMillis = new CounterMetric();

Is there any overriding reason to be unique here, or does it make more sense to just do what we usually do?

[joegallo]

I'd be fine with +1ing the type changes by themselves, but in order to change the logic on the time math, I'm going to have to start by understanding the reason this fence was here in the first place.