[Twisted-Python] process output modulation

[David]

We are streaming a large amount of program output to the browser via a
twisted app, and we are seeing huge memory consumption.

We have a database process that generates large amounts of data to
stdout, and we are streaming that to the browser through a twisted
web2 app.  We are using web2 because it supports upload streaming as
well.

Our code looks like:

        env = {}
        input = stream.MemoryStream('')
        SQLDUMP = '/usr/bin/dump'

        pstream = stream.ProcessStreamer(input, SQLDUMP,
                             [SQLDUMP,'--format=p','--clean',
                              '--host='+cfg.SOCKET,
                              '--username='+self.role,dbname],
                             env)
        pstream.run()

        outstream = WatchedStream(pstream.outStream)

        response = http.Response( headers=headers, stream=outstream)


        class WatchedStream(object):

           def __init__(self,stream):
                self.stream = stream
           def split(self, point):
                ... some implementation
           def close(self):
                ... some implementation
           def read(self):
                d = self.stream.read()
                bufSize = sum( [len(b) for b in self.stream.buffer if b])
                log.msg('buffer size: %s'%bufSize)
                return d

Watching the log shows us that the stream (a web2.ProducerStream)
buffer is growing continuously to hundreds of MB.  Doesn't a stream
object have a bufferSize attribute and the ability to throttle the
flow of data based on buffer fullness?  Does that throttling behavior
have to be triggered explicitly?

Yes, I know that web2 is deprecated, but I don't know that the problem
is in the web2 components.  The reactor.spawnProcess documentation
does not seem to address the matter of modulating the read speed.  Any
assistance will be appreciated.


-- 
dkeeney at travelbyroad.net
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