public void put(Metrics metrics) {
        sessionCache.put(metrics, metrics);
    }
MetricsSessionCache is a key-value cache to hold hot metric in-memory to reduce payload to pre-read.
Every instance of MetricsSessionCache maps to an instance of {@link MetricsPersistentWorker}.

There are two ways to make sure metrics in-cache,
1. Metrics is read from the Database through {@link MetricsPersistentWorker}.loadFromStorage
2. The built {@link InsertRequest} executed successfully.

There are two cases to remove metrics from the cache.
1. The metrics expired.
2. The built {@link UpdateRequest} executed failure, which could be caused
(1) Database error. (2) No data updated, such as the counter of update statement is 0 in JDBC.

@since 9.4.0 Created this from MetricsPersistentWorker.sessionCache.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/worker/MetricsSessionCache.java