[erlang-questions] HTTP client with sessions support

[Ulf Wiger]

> On 13 Jun 2015, at 21:35, Ingela Andin <ingela.andin@REDACTED> wrote:
> 
> Creating a name for the profile is not that heavy?! The ets-table is an implementation detail not written in stone, it could use some other data structure like a dict or something. Feel free make a PR, if you make a good case it can be changed.

Creating an ets table really isn’t a heavy operation.

Consider the following program:

-module(etsc).

-compile(export_all).


t(N) when N > 0 ->
    T = ets:new(t, []),
    ets:delete(T),
    t(N-1);
t(_) ->
    ok.


Eshell V5.10.4  (abort with ^G)
1> c(etsc).
{ok,etsc}
2> timer:tc(etsc,t,[1000]).
{2775,ok}
3> timer:tc(etsc,t,[1000]).
{2612,ok}
4> timer:tc(etsc,t,[1000]).
{2055,ok}
5> timer:tc(etsc,t,[1000]).
{1881,ok}

That is, on my old Macbook Air, it takes about a microsecond to create an ets table*.

Creating an atom is also obviously cheap, but I cringe a bit when list_to_atom/1 is used in generic code - although in this particular case, I guess creating memory leaks because of it is not very likely.

BR,
Ulf W

* Obviously, this test doesn’t accumulate ets tables. I removed the ets:delete/1 call, and things looked much worse:
- Creating the first 1000 tables took ca 13 ms.
- Creating 1000 tables when there were already 67K tables, took 6.2 seconds.
- However, creating an ets table from another process was still pretty fast - ca 10 usec
I conclude that having thousands of ets tables owned by a single process is a *bad* idea (probably not for this reason alone).

Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.
http://feuerlabs.com



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