https://docs.google.com/document/d/1kPIM8Q67wMUBchwym0Fxjp4mtHSaJLwbuuvfxZ8nn28/edit

• Increase the snap-handle-pool-size setting can improve the speed of applying region snapshots.
• Reduce the memory usage during applying region snapshots, from 3 copies to at most 2 copies.
• Use multiple Blocks to store the data of region snapshots.