Hi Todd, Good paper, it would be nice to get the Flush-Pipelining technique (described in the paper) implemented in HBase and HDFS write-ahead logs. (I am CC-ing this to hdfs-...@hadoop as well)
HDFS currently uses Hadoop RPC and the server thread blocks till the WAL is written to disk. In earlier deployments, I thought we could safely ignore flush-pipelining by creating more server threads. But in our largest HDFS systems, I am starting to see 20% sys-time usage on the namenode machine; most of this could be thread scheduling. If so, then it makes sense to enhance the logging code to release server threads even before the WAL is flushed to disk (but, of course, we still have to delay the transaction response to the client till the WAL is synced to disk). Does anybody have any idea on how to figure out what percentage of the above sys-time is spent in thread scheduling vs the time spent in other system calls (especially in the Namenode context)? thanks, dhruba On Fri, Dec 24, 2010 at 8:17 PM, Todd Lipcon <t...@cloudera.com> wrote: > Via Hammer - I thought this was a pretty good read, some good ideas for > optimizations for our WAL. > > http://infoscience.epfl.ch/record/149436/files/vldb10aether.pdf > > -Todd > -- > Todd Lipcon > Software Engineer, Cloudera > -- Connect to me at http://www.facebook.com/dhruba
