Hi Barry,
Thanks for the response. Where can I read more about (1). It seems
like that is something I need to explore.
As we already have (2) (cache for each process).
Thanks again for your help.
On Wed, Nov 6, 2019 at 8:39 AM Scott, Barry <barry.sc...@forcepoint.com>
wrote:
> On Wednesday, 6 November 2019 14:21:22 GMT Maarten ter Huurne wrote:
> > On Wednesday, 6 November 2019 07:19:56 CET Waqar Khan wrote:
> > > Hi,
> > > So, I am writing a twisted server. This server spawn multiple child
> > > processes using reactor spawnProcess that initializes a process
> > > protocol.
> > >
> > > Now, each of the childprocess receives some REST requests. Each
> > > process has a dict that acts as cache.
> > > Now, I want to share dict across processes.
> > > In general, python has SharedMemoryManager in multiprocessing module
> > > which would have helped.
> > > https://docs.python.org/3/library/multiprocessing.shared_memory.html#m
> > > ultiprocessing.managers.SharedMemoryManager.SharedMemory But since I
> > > am using twisted internal process implementation, how do I share this
> > > dict across the processes so that all the processes use this common
> > > cache?
> >
> > Keeping a dictionary in SharedMemoryManager seems far from trivial. I
> > don't think you can allocate arbitrary Python objects in the shared
> > memory and even if you could, you would run into problems when one
> > process mutates the dictionary while another is looking up something or
> > also mutating it.
> >
> > It could in theory work if you implement a custom lock-less dictionary,
> > but that would be a lot of work and hard to get right. Also having
> > shared memory mutations be synced between multiple CPU cores could
> > degrade performance, since keeping core-local CPU caches in sync is
> > expensive.
> >
> > Would it be an option to have only one process accept the REST requests,
> > check whether the result is in the cache and only distribute work to the
> > other processes if you get a cache miss? Typically the case where an
> > answer is cached is pretty fast, so perhaps you don't need multiple
> > processes to handle incoming requests.
>
> We have used a couple of ways to cache.
> 1. Use a singleton process to hold the cache and ask it, via IPC, for
> answers
> from the other process.
> 2. have a cache in each process
>
> Barry
>
>
> >
> > Bye,
> > Maarten
> >
> >
> >
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>
>
>
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