Can there be limits on message queue length?

[Ulf Wiger (AL/EAB)]

David Hopwood wrote:

> Hmm, the "Erlang specification" pointed to by the FAQ seems 
> to be the "Erlang 4.7.3 Reference Manual, DRAFT (0.7)" dated 
> February 1999.
> Is this really the most up-to-date written specification of Erlang?

As far as ambitious specifications go, I guess it is. However, 
the Erlang Reference Manual
(http://erlang.se/doc/doc-5.4.12/doc/reference_manual/part_frame.html)
is at least much more up-to-date.


> Anyway, this specification doesn't appear (by skimming 
> section 10) to say whether there are, or are required not to 
> be any limits (besides heap size) on message queue length.

The most informative (and up-to-date) text on system limits is 
most likely the "System Limits" chapter (7.2) of the efficiency
guide in the Erlang/OTP documentation:

http://erlang.se/doc/doc-5.4.12/doc/efficiency_guide/advanced.html#7.2

I spotted at least one error in there: It says that the 
maximum number of processes can be 268435456, when in fact
it was changed to 134217727 as of erts-5.4.9.

The System Limits document doesn't say anything specific about
message queues. As far as I can tell from erl_message.c, messsage
buffers are pretty much handled like other objects on the process
heap, i.e. limited only by available memory.

/Uffe