On Sep 11, 2009, at 2:41 PM, Doug Cutting wrote:
I'm considering an HTTP-based transport for Avro as the preferred,
high-performance option.
HTTP has lots of advantages. In particular, it already has
- lots of authentication, authorization and encryption support;
- highly optimized servers;
- monitoring, logging, etc.
Q. Is this to replace the client-DN data-transfer protocol or for ALL
Hadoop rpc?
Q. Was authentication one of your main motivation?
The current plans for authentication is centered around kerberos.
HTTP does not fit in too well in that picture.
sanjay
Tomcat and other servlet containers support async NIO, where a
thread is
not required per connection. A servlet can process bulk data with a
single copy to and from the socket (bypassing stream buffers). Calls
can be multiplexed over a single HTTP connection using Comet events.
http://tomcat.apache.org/tomcat-6.0-doc/aio.html
Zero copy is not an option for servlets that generate arbitrary data,
but one can specify a file/start/length tuple and Tomcat will use
sendfile to write the response. That means that while HDFS datanode
file reads could not be done via RPC, they could be done via HTTP with
zero-copy. If authentication and authorization are already done in
the
HTTP server, this may not be a big loss. The HDFS client might make
two
HTTP requests, one to read a files data, and another to read its
checksums. The server would then stream the entire block to the
client
using sendfile, using TCP flow control as today.
Thoughts?
Doug
