Thanks for the blog post, very interesting read. Some questions ... 1. Are the operations "Writes mutation to tablet servers’ WAL/Sync or flush tablet servers’ WAL" and "Adds mutations to sorted in memory map of each tablet." performed by threads in parallel?
2. Could the latency of hsync-ing the WALs be overcome by modifying Accumulo to write them to a separate SSD-only HDFS? To maintain data locality it would require two datanode processes (one for the HDDs and one for the SSD), running on the same node, which is not hard to do.
