[erlang-questions] Erlang http servers
Mon Oct 1 21:52:53 CEST 2012
On 10/01/2012 08:11 PM, Kenneth Lundin wrote:
> > * OTP has a long release process. Many companies need their fixes to
> be included quickly to avoid maintaining huge branches for their
> changes. They generally agree in return to keep track of changes that
> might happen during the product's development.
> I think we are pretty fast with service releases about every 3rd month
> and updates on the maint branch in git between that.
But doesn't that imply upgrading the whole of OTP? If it does, that
means more testing and more chances for new issues. If you can build a
release upgrade with one app from one OTP version and the rest from a
previous version, I'd like to know how.
> > Note that while not everyone uses inets, most servers do use
> erlang:decode_packet/3 which does most of the job. Cowboy doesn't
> anymore, because it needed backward incompatible changes to
> erlang:decode_packet/3. I didn't ask your thoughts, simply because the
> experiment I did hinted that doing the parsing in full Erlang was a
> better idea: this change results in improved HiPE optimizations and
> better reduction management which results in better latency under load.
> Interesting, would be good if you could give us more info on this. The
> http parsing in
> decode_packet is there to improve performance. If it is not ( without
> using HiPE) we should consider removing it!
Between now and then binaries appeared, got performance improvements,
and considering Cowboy is full binary (no conversion to atom for methods
or header names or anything) and only receives requests, not responses,
that means it can skip many steps that decode_packet/3 can't.
Binaries also mean you can parse the request line and all the headers
using a single match context which seems to be very fast (good job!) and
I'm guessing is the main reason for improved performance under HiPE (I'm
about to start reading the HiPE papers to understand that better).
> >> In Erlang/OTP we have keep strict compatibility with many of our APIs
> >> which is both a strength and sometimes a burden (when we are not happy
> >> with the old API) but there are mostly ways around that if there is
> >> strong case for a change.
> > It's a big strength for people looking for stability and a big burden
> for people looking for reactivity. Can't really blame the second group
> for finding solutions to their problems.
> I am not blaming people
I used a word too strong there. :)
> for implementing their own solution, it is good
> to have a lot to choose from. But I still think the stability is very
> important for the majority of users making systems with a longer life
> cycle than a year.
> Our experience is that we have to be very compatible in order to
> convince our
> users (often big projects) to step up to our latest release.
> By this we can also stop supporting older versions.
Yes and I wouldn't want that to stop, that's a strong point. In fact
having both ways is great, it means you can make sure the important
parts of your system are stable while the more bleeding-edge parts are
kept, well, bleeding-edge.
> >> I think it is of great value to have a relative complete functionality
> >> in Erlang/OTP so that
> >> the user can implement basic functionality without having to search
> >> for separate implementations of, with unknown quality and completeness
> >> at least for a beginner.
> > I would prefer Erlang/OTP to focus on the core features and leave the
> satellite features to third parties. OTP has an HTTP server but doesn't
> have proper Unicode support. OTP has OpenGL but doesn't have proper
> timezones support. These 2 examples missing from OTP are some of many
> things that are too complex for most people to implement, and that would
> not benefit from having alternatives.
> What is missing when it comes to timezones? Has it been mentioned in
> another thread?
> I think we rely on the OS configuration here.
Date/time conversion from one timezone to another. For example if your
data is saved with UTC time but the user is in Paris you want to convert
it to Europe/Paris.
Perhaps it exists, but I haven't found it.
I think there's a lot of work to be done with regards to localization
and internationalization support, but I haven't had enough time to think
about it in details yet. Unicode (not just Unicode though, but a native
string type abstracting encodings, EEP coming in a few weeks),
timezones, graphical drawing libraries are pretty much what I find lacks
the most for the web side of things. Graphical drawing libraries are
fine outside of OTP for a while (until there's one that can do near
everything and do it well) though.
Thanks for the info on package management and bug tracker. Hope we'll be
involved in the process of creating the former. And thanks for your nice
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