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| garry |
 Posted: Tue Aug 11, 2009 7:07 pm |
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User
Joined: 11 Aug 2009
Posts: 11
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i am in the process of rewriting an old app in terms of current erlang/otp.
as part of that, i hope to take advantage of the ssh module to provide secure
remote access from python. part of the motivation for this is to reduce complexity
vs. the current interface, and to hopefully achieve some performance gains by
eliminating the overhead of xmlrpc processing.
i have the basics working now, but have been surprised to find that the new system
is considerably slower, by a factor of 3 or so, than the old one. the guts of the
two remain the same for the most part; just the interface has changed. to clarify
things, i hacked up the code a bit so the new one does nothing but echo the text
sent to it, while the old one does all of its normal processing (mysql queries,
aggregation, encodeing/decoding, etc). this minimal new one is still 3 times slower.
the old interface began as a hand-rolled xmlrpc interface, built using xmerl (0.17)
and joe armstrong's pico server framework. later, when it was necessary to secure
it, someone modified the remote python client lib to use ssh to launch a local python
server, which used the xmlrpc interface to talk to the erlang server and send back
the results.
i want to eliminate this excess code, as well as the overhead of xml encoding/decoding.
the new code uses the erlang ssh module, somewhat like this (edited):
init() ->
Opts = [ { shell, fun( U, H ) -> start_repl( U, H ) end } ],
{ ok, DaemonRef } = ssh:daemon( any, Port, Opts ).
...
start_repl( User, Peer ) ->
spawn( fun() -> read_eval_print_loop() end ).
% simple Read-Eval-Print loop
read_eval_print_loop() ->
Line = io:get_line( { format, "", [] } ),
io:format( "~s~n!~n", [ Line ] ),
read_eval_print_loop().
so the question is, is the performance i'm seeing to be expected?
are there known issues around the ssh module performance? am i
doing something dumb? are there better ways to use this (or related)
modules, or other approaches altogether?
it occurs to me the problem could be with my use of io:get_line()
and io:format(). is the io module the problem? the messages i'm sending are small, perhaps 50 chars. are there better ways of
doing that?
any insight would be appreciated. i really like the approach of being
able to talk to our servers this way.
thanks |
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| bpuzon |
| Posted: Thu Aug 13, 2009 8:24 am |
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Joined: 05 Aug 2009
Posts: 23
Location: Cracow, Poland
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| garry |
| Posted: Thu Aug 13, 2009 3:14 pm |
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Joined: 11 Aug 2009
Posts: 11
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> Which erlang version are you using?
R13B
> The io:get_line performance was improved
then perhaps it's in the ssh module. |
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