[erlang-questions] Trying to understand the performance impact of binary:split/3
Wed May 20 13:29:07 CEST 2015
Well I'll be damned. I thought I read somewhere that binary module was
implemented in erlang (not bifs) which was why it was slow. I guess I never
checked. I take my statements back :)
On Wed, May 20, 2015 at 1:14 PM, José Valim <jose.valim@REDACTED
> Thank you Sergej.
> I have created a branch that uses the split version you mentioned and it
> is 4x times slower than using binary:split/3. Here is the commit that added
> the new implementation:
> *José Valim*
> Skype: jv.ptec
> Founder and Lead Developer
> On Wed, May 20, 2015 at 12:56 PM, Sergej Jurečko <sergej.jurecko@REDACTED
> > wrote:
>> binary:split is not fast and unfortunately many people do not realize
>> If you want speed, here is an implementation that is made for speed:
>> On Wed, May 20, 2015 at 12:35 PM, José Valim <
>> jose.valim@REDACTED> wrote:
>>> Hello folks,
>>> At the beginning of the month, someone wrote a blog post comparing data
>>> processing between different platforms and languages, one of them being
>>> Erlang VM/Elixir:
>>> After running the experiments, I thought we could do much better. To my
>>> surprise, our biggest performance hit was when calling binary:split/3. I
>>> have rewritten the code to use only Erlang function calls (to make it
>>> clearer for this discussion):
>>> The performance in both Erlang and Elixir variants are the same
>>> (rewritten in Erlang is also the same result). This line is the bottleneck:
>>> In fact, if we move the regular expression check to before the
>>> binary:split/3 call, we get the same performance as Go in my machine.
>>> Meaning that binary:split/3 is making the code at least twice slower.
>>> The binary:split/3 implementation is broken in two pieces: first we find
>>> all matches via binary:matches/3 and then we traverse the matches
>>> converting them to binaries with binary:part/3. The binary:part/3 call is
>>> the slow piece here.
>>> *My question is:* is this expected? Why binary:split/3 (and
>>> binary:part/3) is affecting performance so drastically? How can I
>>> investigate/understand this further?
>>> ## Other bottlenecks
>>> The other two immediate bottlenecks are the use of regular expressions
>>> and the use of file:read_line/3 instead of loading the whole file into
>>> memory. Those were given as hard requirements by the author. None the less,
>>> someone wrote an Erlang implementation that removes those bottlenecks too
>>> (along binary:split/3) and the performance is outstanding:
>>> I have since then rewritten the Elixir one and got a similar result.
>>> However I am still puzzled because using binary:split/3 would have been my
>>> first try (instead of relying on match+part) as it leads to cleaner code
>>> *José Valim*
>>> Skype: jv.ptec
>>> Founder and Lead Developer
>>> erlang-questions mailing list
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