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 performance of before/after HBASE-21879, we build the following clusters. And we have designed three test cases to prove the performance improvement after HBASE-21879: 1. Disabled BlockCache cache Gets read HDFS directly in before-HBASE-21879 case then it will make so many heap allocations and have a very high GC pressure on heap, while after HBASE-21879 all reads will allocate from pooled offheap