[erlang-questions] 64-bit erlang

Tomas Abrahamsson <>
Wed Nov 28 11:49:34 CET 2007


> We've had reason to start discussing 64-bit Erlang, and
> I thought I'd share some thoughts, hoping that others will
> share theirs.
>
> In one application, we're starting to hit the 4 GB ceiling,
> and we're discussing ways to address the situation. One
> option is to install more RAM, but then we need to either
> run multiple nodes on each machine (affects software
> complexity), or switch to 64-bit Erlang.
>
> But 64-bit Erlang consumes up to twice as much memory as
> 32-bit Erlang, so if we switch to more expensive RAM and
> install 8 GB, worst case, we'll still have roughly the
> same capacity. The cost per GB goes up, which cuts into
> the per-unit profit margin.

We start several erlang virtual machines and spread the
application over these.

The 4 GB ceiling is one reason for this (our only
remaining, I guess). In the pre-smp times, this was
also a way of making use of the computing power in
multicpu machines.

We've also tried the 64-bit Erlang from a performance
persective, but concluded that the 32-bit Erlang is
faster for our application. In addition to using more
main memory, it'd also use more CPU cache due to its
larger pointers.

> After all, I doubt that anyone is seriously looking at having
> process heaps larger than 4 GB...

We haven't hit _that_ limit yet :-)


/Tomas



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