Chris Reynolds wrote:
> >We currently run all our apps from the server. Is there a
> significant speed
> >difference (for the user), if the apps are on their PC? (Our
> database would
> >still be on a server). Also, is there significant improvement in network
> >performance? We average around 60 users.
> >
> Typical bandwidth on a 10mb LAN is often around 500Kb/sec so if
> your app is 2MB say, that is a 4 seconds more than a local load
> time (assuming lots of other issues
> don't siginificantly affect it.)
Yeah, 500Kb/sec is about right (maybe slightly high) as 10 Mega-bits per
second = 1.25 Mega-bytes per second. But that's peak utilisation of 100%
efficiency and due to the 802.3 protocol (collision sensing and exponential
back-offs), getting higher than 30% utilisation on a shared segment is rare.
So, that's about 375Kb/sec but that's if I remember my Uni papers correctly
and it's quite a while ago now :-)
Switches help this considerably by giving each client 10Mb (or more) full
duplex dedicated bandwidth but all clients are still sharing (or competing
for) the server's single 10Mb path to the switch and causing hard drive head
movement (seek latency) as it moves the head from code to data areas of the
drive.
Also, another factor is applications don't load all in one go and stay put,
they're paged on demand in 4K chunks (usually). So there is usually an
initial pause on startup as lots of library code and resources are brought
across and then there are other smaller pauses as new pages of code are
brought in.
Now, if the client is RAM-starved (sadly, all too common), code pages will
get evicted and these will then need to be refetched across the network
which can cause other pauses. Eviction and refetch is bad but can be
tolerable at local drive throughput rates - it's an order of magnitude worse
across 10Mb network and lowers the thrashing threshold considerably
(thrashing is the state of continuous eviction and refetching of pages to
the point that hardly any actual 'work' is done)
So, there are lots of variables here. Also, we 'guard' more than just the
application - we guard and replicate the help, full PDF manuals, external
(to the app) config files for when the Australian Tax Office changes it's
XML formats and DTDs (again!), etc.
Generally speaking, I tend to treat network bandwidth as our most precious
(and limited) resource, as much out of engineering 'habit' as anything :-)
Otherwise, you can find your fresh new app which runs like a scalded cat on
your high-specced company workstation and network crawls like a strangled
fart for the client.
TTFN,
Paul.
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