Re: Performance monitor signal handler

* Jan Wieck <JanWieck(at)Yahoo(dot)com> [010316 16:35]:
> Jan Wieck wrote:
> > Tom Lane wrote:
> > > Now this would put a pretty tight time constraint on the collector:
> > > fall more than 4K behind, you start losing data. I am not sure if
> > > a UDP socket would provide more buffering or not; anyone know?
> >
> > Looks like Linux has something around 16-32K of buffer space
> > for UDP sockets. Just from eyeballing the fprintf(3) output
> > of my destructively hacked postleprechaun.
>
> Just to get some evidence at hand - could some owners of
> different platforms compile and run the attached little C
> source please?
>
> (The program tests how much data can be stuffed into a pipe
> or a Sys-V message queue before the writer would block or get
> an EAGAIN error).
>
> My output on RedHat6.1 Linux 2.2.17 is:
>
> Pipe buffer is 4096 bytes
> Sys-V message queue buffer is 16384 bytes
>
> Seems Tom is (unfortunately) right. The pipe blocks at 4K.
>
> So a Sys-V message queue, with the ability to distribute
> messages from the collector to individual backends with
> kernel support via "mtype" is four times by unestimated
> complexity better here. What does your system say?
>
> I really never thought that Sys-V IPC is a good way to go at
> all. I hate it's incompatibility to the select(2) system
> call and all these OS/installation dependant restrictions.
> But I'm tempted to reevaluate it "for this case".
>
>
> Jan
$ ./queuetest
Pipe buffer is 32768 bytes
Sys-V message queue buffer is 4096 bytes
$ uname -a
UnixWare lerami 5 7.1.1 i386 x86at SCO UNIX_SVR5
$

I think some of these are configurable...

LER

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Larry Rosenman http://www.lerctr.org/~ler
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