On 06/07/11 11:08, Rita wrote:
I have many large files ranging from 2gb to 800gb and I use hadoop fs -cat a
lot to pipe to various programs.
I was wondering if its possible to prefetch the data for clients with more
bandwidth. Most of my clients have 10g interface and datanodes are 1g.
I was thinking, prefetch x blocks (even though it will cost extra memory)
while reading block y. After block y is read, read the prefetched blocked
and then throw it away.
It should be used like this:
export PREFETCH_BLOCKS=2 #default would be 1
hadoop fs -pcat hdfs://namenode/verylarge file | program
Any thoughts?
Look at Russ Perry's work on doing very fast fetches from an HDFS filestore
http://www.hpl.hp.com/techreports/2009/HPL-2009-345.pdf
Here the DFS client got some extra data on where every copy of every
block was, and the client decided which machine to fetch it from. This
made the best use of the entire cluster, by keeping each datanode busy.
-steve
