[SAC] ProjectsVM Upgrade Problem

Martin Spott Martin.Spott at mgras.net
Fri Feb 10 03:57:02 EST 2012


The closer I look at the issue, the more I'm uncertain wether blocking
IP's is the right way to deal with the performance drop on the
"projects" VM.  I think it's worth considering the following items:

1.) This system is having access to four CPU's and 8 GByte RAM, but
    the CPU's are idle most of the time and the system is hardly making
    any use of the available RAM.
2.) The I/O load is pretty close to idle.
3.) The Apache is serving approx. 50 to 70 requests per second (much
    easier to count now that Apache log rotation works again  ;-))
    The number is surprisingly high at the first glance, but given the
    fact that most of these requests don't cause any disk I/O -
    except from writing access- and error-log - that's not much. 
    Indeed, the system is doing more disk-writes than reads.
4.) Stopping the sr.org server doesn't make a relevant difference in
    response times of the GRASS web page for example.
5.) A busy file server on this sort of hardware should be capable of
    serving at least 50 to 80 MByte per second while delivering 1k or
    more packets per second and reading approx. 15k to 20k blocks from
    the disk at the same time.  Thus, the load caused by these 50 to 70
    misguided HTTP requests per second is quite small compared to what
    the platform should be able to fulfill.
6.) I can't imagine why this HTTP load didn't occur before the
    dist-upgrade ....

I might be wrong, but, as a consequence of the above, my expectations
into curing the current performance issue on the "projects" VM by
blocking individual IP's or ranges of IP's are not very high any more. 

I think we'll have to look elsewhere in order to identify the cause
....  but I'd still like to try installing my semi-automated IP block
as a test for a day or two.

Cheers,
	Martin.
-- 
 Unix _IS_ user friendly - it's just selective about who its friends are !
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