a bad performance or even not working when the number of region is very large, e.g 1000+ per regionserver Create WriterAndPath Create WriterAndPath Create WriterAndPath Create WriterAndPath appendBuffer of region * number of replica * number of regionserver Streams each datanode need to handle = Number of streams / number of datanodes Number of regionserver usually equals to number of datanodes. ❏ bounded = true ❏ Configurations: hbase.regionserver.hlog.splitlog.buffersize (maxHeapUsage): set it equals or larger than the size limit of HLog. hbase.regionserver.hlog.splitlog.writer.threads : Not having

Amplification When Using Blocking Client RegionServer RegionServer RegionServer Handler-1 Handler-2 Handler-3 Services RegionServer RegionServer RegionServer Handler-1 Handler-1 Handler-1 Services 256 MB ○ hbase.bucketcache.ioengine = offheap Test Environment RegionServer RegionServer RegionServer RegionServer RegionServer HMaster ● Java: JDK 1.8.0_111 ● Heap: 30G Heap + 30G OFF-Heap

Side HBase Client ClientScanner ClientScanner cache(queue) scanner.next() RegionServer-0 RegionServer-1 RegionServer-2 scanResultCache ScannerCallableWithReplicas 1. RPC Request 2. RPC Response Result-1 Cell-4 Result-3 Cell-5 Result-4 Cell-7 Result-5 Cell-6 Cell-8 Cell-2 Result-2 Cell-3 RegionServer Row Data RPC Response Recieved from RS Results get from scanner.next() Cell-9 Size of cell-1 Result-1 Cell-4 Result-3 Cell-5 Result-4 Cell-7 Result-5 Cell-6 Cell-8 Cell-2 Result-2 Cell-3 RegionServer Row Data RPC Response Recieved from RS Results get from scanner.next() Cell-1 Cell-2 Result-1

pre-allocate 2MB *2 for each RPC handler ( The handler count is determined by the config: hbase.regionserver.handler.count, it has the default value 30) . That’s to say, if your ​hbase.server.allocator request), then it will be better to increase the hbase.server.allocator.max.buffer.count. The RegionServer web UI also has the statistic about ByteBuffAllocator: If the following condition meet