2i stale=ok latency memdb - investigation

For build 1798, memdb state=ok scan latency is at 1.9ms. Looking at indexer log, indexer latency is about 300us (excluding protobuf overhead). Scan throughput is at 60K-80K. Mutation throughput is at 90K-100K. Aggregated throughput at 150K-180K on 3000-3500% cpu utilization.

For node .122 (indexer), out-byte is 20-30MB/s, and in-byte is 30-40MB/s. This is about 560Mb/s. So network should not be saturated.

With indexer latency at 300us, I would expect scan latency to be at 1ms.