[Rd] Is it a good choice to increase the NCONNECTION value?
m@ech|er @end|ng |rom @t@t@m@th@ethz@ch
Tue Aug 24 10:44:35 CEST 2021
>>>>> qweytr1--- via R-devel
>>>>> on Tue, 24 Aug 2021 00:51:31 +0800 (GMT+08:00) writes:
> At least in 2015, a github user, tobigithub, submit an
> [issue](https://github.com/sneumann/xcms/issues/20) about
> the error "Error in file(con, "w") : all connections are
> in use" Nowadays, since AMD have really cool CPUs which
> increases the thread numbers to 128 or even 256 on a
> single server, we found that the NCONNECTIONS variable
> could prevent us from utilizing all the 128 threads. It
> might be a good choice to increase its value.
> the variable is defined in
> `R-4.1.1/src/main/connections.c: 17` I have tested that,
> increase it to 1024 generates no error and all the
> clusters (I tried with 256 clusters on my 16 threads
> Laptop) works fine.
> Is it possible increase the size of NCONNECTION?
Yes, of course, it is possible.
The question is how much it costs and to which number it should
A quick look at the source connections.c --> src/R_ext/include/Connections.h
reveals that the Rconnection* <--> Rconn is a struct with about
200 chars and ca 30 int-like plus another 20 pointers .. which
would amount to a rough 400 bytes per connection.
Adding 1024-128 = 896 new ones would then amount to increase
the R executable by about 360 kB .. all the above being rough.
So personally, I guess that's "about ok" --
are there other things to consider?
Ideally, of course, the number of possible connections could be
increased dynamically only when needed
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