private void updateBufferMetrics() {
        bufferSizeSensor.record(memBufferSize, context.currentSystemTimeMs());
        bufferCountSensor.record(index.size(), context.currentSystemTimeMs());
    }
As of 2.1, there's no way for users to directly interact with the buffer,
so this method is implemented solely to be called by Streams (which
it will do based on the {@code cache.max.bytes.buffering} config.
<p>
It's currently a no-op.
streams/src/main/java/org/apache/kafka/streams/state/internals/InMemoryTimeOrderedKeyValueChangeBuffer.java