HBASE-21879 Read HFile ’s Block into ByteBuffer directly. 1. Background For reducing the Java GC impact to p99/p999 RPC latency, HBase 2.x has made an offheap read and write path. The KV are allocated didn’t accomplish this before because HDFS does not support the ByteBuffer pread interface, also because of its complexity. For the ByteBuffer pread, we have issue ​HDFS-3246​ to track this, so further HDFS can also be easy as the 3.1 part described. 3.3 Make downstream API can accept ByteBuff or ByteBuffer as arguments The first obstacle when implementing the block off-heap reading is: many downstream