My OTP-21 highlights

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_posts/2018-5-02-My-OTP-21-Highlights.md

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+---
+layout: post
+title: My OTP 21 Highlights
+tags: otp 21 release
+author: Lukas Larsson
+---
+
+OTP-21 Release Candidate 1 has just been released. I thought that I would go
+through the changes that I am the most excited about. Most likely this will
+mostly mean features in erts and the core libraries as those are the
+changes that I am the most familiar with.
+
+You can download the readme describing the changes here: [OTP 21-RC1 Readme](http://erlang.org/download/otp_src_21.0-rc1.readme).
+Or, as always, look at the release notes of the application you are interested in.
+For instance here: [OTP 21-RC1 Erts Release Notes](http://erlang.org/doc/apps/erts/notes.html).
+
+# Compiler / Interpreter #
+
+Björn Gustavsson has been doing a lot of work with the compiler and interpreter
+the last year while I have been sitting next to him cheering. The largest changes
+is part of the OTP-14626 ticket. While working on the
+[BEAMJIT](https://www.youtube.com/watch?v=PtgD5WRzcy4) development
+I've been looking a lot at the [luajit](http://luajit.org/) project and what
+Mike Pall has done both in the JIT but also in the interpreter. Inspired by
+this and some other ideas that we got from the BEAMJIT project we decided it was time
+to do a major overhaul of the way that the BEAM interpreter is created. Most of the
+changes done boil down to decreasing the size of beam code in memory, thus making more
+code fit in the L1/L3 caches and in extension making code run faster. We've
+decreased the loaded code size by about 20% using our optimizations. This has
+translated to about a 5% performance increase for most Erlang code
+which is quite amazing. Me or Björn will most likely write more about exactly
+what this has entailed in a future blogpost.
+
+Another compiler change that has had quite a large impact (at least in our benchmarks)
+is OTP-14505 contributed by José Valim in [PR 1080](http://github.com/erlang/otp/pull/1080).
+The change makes the compiler re-write:
+
+    example({ok, Val}) -> {ok, Val}.
+
+to
+
+    example({ok, Val} = Tuple) -> Tuple.
+
+eliminating the extra creation of the tuple. As it turns out this is a quite
+common pattern in Erlang code so this will be good for all programs.
+
+An example of this performance gain can be seen in the estone benchmarks SUITE
+below. OTP-14626 together with some other compiler and erts improvements have
+increased the number of stones from 370000 in OTP-20.3 (the green line), to
+400000 in OTP-21 (the blue line). So about 7.5%.
+
+![Estone OTP-21 benchmark](../images/estone_otp21_benchmark.png)
+
+# Erlang run-time system #
+
+There are many changes in the run-time system.
+
+## File handling ##
+
+All file IO has traditionally been handled through a port. In OTP-21 all of the
+file IO has been rewritten to use nifs instead, OTP-14256. This was mainly done
+in order to run file operation in the dirty IO schedulers. It also had the nice
+side-effect of significantly increasing throughput of certain operations.
+
+![File tiny reads OTP-21 benchmark](../images/file_tiny_reads_otp21_benchmark.png)
+
+For instance in the tiny reads benchmark OTP-21 (the blue line) is about 2.8 times
+faster than OTP-20.3 (the green line).
+
+Also it is now possible to open device files using file:open, see OTP-11462.
+
+## I/O Polling ##
+
+The entire underlying mechanism for checking for I/O on sockets has been rewritten
+and optimized for modern OS kernel polling features. See OTP-14346 and
+[I/O polling options in OTP 21]({{ site.baseurl }}/IO-Polling) for more details.
+
+## Distribution ##
+
+It has always been possible to write your own distribution carrier if you want
+to if, for instance, you wanted to use [RFC-2549](https://tools.ietf.org/html/rfc2549)
+to send your distributed Erlang messages. However you have had to implement it as
+a linked-in driver. With the introduction of OTP-14459 you can now use a process
+or port as the distribution carrier. So now you can use gen_pigeon instead of having
+to call the boost equivalent.
+
+The ability to use processes as distribution carriers is now used by the TLS
+distribution. This allows us to not have to jump through several hoops as was done
+before increasing the throughput of TLS distribution significantly.
+
+## Process signals ##
+
+When running benchmarks using cowboy and hammering it with connections that
+do not use keep-alive, one of the SMP scalability bottlenecks that pop up
+is the link lock of the supervisor that supervises all the connections.
+The reason why this lock pops up is because when you have a lot of linked
+processes, the rb-tree in which the links are stored becomes very large so
+the insertion and deletion time increases. In OTP-14589 this has been
+changed so that all link and monitor requests now are sent as messages
+for the receiving process to take care of. This means that the lock has been
+completely removed. Now all signals (be they messages, links, monitors,
+process\_info, group\_leader etc) are handled through the same queue.
+
+In addition, OTP-14901 now makes it so that monitor + send signals
+are merged into one signal. So the contention is reduced even further
+for gen_server:call like functions.
+
+![GenStress OTP-21 benchmark](../images/genstress_otp21_benchmark.png)
+
+The performance difference is quite significant. The genstress benchmark
+seen above OTP-21 (the blue line) has almost doubled in throughput
+compared to OTP-20.3 (the green line).
+
+# Logger
+
+OTP-13295 adds a completely new logging framework for Erlang/OTP. It is
+inspired by the way that [lager](https://github.com/erlang-lager/lager),
+the [Elixir Logger](https://hexdocs.pm/logger/Logger.html) and the [Python
+logger](https://docs.python.org/3/howto/logging.html) works.
+With logger the logging handlers can intercept the logging
+call in the process that does the actual call instead of having to
+wait for a message. This opens up all sorts of possibilities of early
+rejection of log messages in case of an overload, see [Logger User's Guide](http://erlang.org/documentation/doc-10.0-rc1/lib/kernel-6.0/doc/html/logger_chapter.html#protecting-the-handler-from-overload)
+for more details. The user can also add special purpose filters that are run
+before the handler is invoked in order to silence or amend log messages in the system.
+
+# Misc
+
+HiPE has finally been fixed by Magnus Lång to use the receive reference optimization
+that beam has had for a long time, OTP-14785.
+
+The ftp and tfpt parts of inets have been separated into their own applications
+instead of being bundled, OTP-14113.
+
+The rand module has seen a lot of work, adding new features. I'm not sure when or
+how the difference is use full, but the theory around this is fascinating, OTP-13764.
+
+The maps module now has an maps:iterator/0 and maps:next/1, OTP-14012.
+
+io_lib:format/3 has been added to limit the output of the functions. This is especially
+useful when building logging frameworks as you may get arbitrarily large terms to
+format and may want to cut them in order to not overwhelm the system, OTP-14983.
+
+As a final note, I'm not sure if anyone noticed, but as of OTP-20.3, processes that
+are in the state GARBING when your system crashes now have stack traces in the
+crash dump!!!