The client will block after the buffer is full, and will wait until the outstanding requests are ack'd from the server. So the times will still be pretty close

The client will block after the buffer is full, and will wait until the outstanding requests are ack'd from the server. So the times will still be pretty close to correct. Only the last few puts won't be timed. https://github.com/elliottneilclark/hbase/blob/trunk/hbase-server/src/main/java/org/apache/hadoop/hbase/client/HTable.java#L828 https://github.com/elliottneilclark/hbase/blob/trunk/hbase-s... So I created a pull request for YCSB so that last little bit of the buffer is counted for HBase.