[Spread-users] Spread scaling
alex at alex.org.uk
Tue Nov 4 04:28:41 EST 2008
This is the first of five (possibly newbie - sorry) questions about spread.
I've split them up into separate emails for ease of reply and to
help others search.
1. The environment I am evaluating using spread in will have a number of
machines that may reach the low single digit thousands. Life would be
greatly simplified if these are within a single domain. There will be
a maximum of 10 clients on each machine. Connectivity between machines
is gigabit and uncontended, and I am not that fussed about total
latency (under a second would be fine) though obviously the faster the
Spread's documentation (possibly outdated) and a mailing list
says there is a hard limit of 127/128 machines at the protocol
level (i.e. I can't just adjust a compile time constant). Is that
still correct in 4.0 given the dynamic membership stuff?
My environment is homogenous (i.e. I cannot use several unconnected
instances of spread). I cannot run spread daemons on a subset of
machines only with each node only connecting to one machine, because
the whole point is to detect machine/process failure and death of
the machine running the spread node will be too catastrophic. I could,
in theory, somehow run spread on say 5% of the machines, and make
each machine try and connect to 3 of them, failing over. However,
I am not convinced this would still result in reliable delivery and
no message disordering. I could also, in theory, run (say) 20 separate
instances of spread and construct an "interdomain router" (to borrow
some old terminology) and route messages between them. Doing this
reliably (e.g. coping with the failure of the router means having
more than one of them) sounds horribly complicated and like it would be
easier to reengineer spread.
2. Assuming I can fix (1), there also seems to be a limit of 127 machines
per segment. All machines will be on the same switched L2 gig ethernet
fabric. Of course I can arbitrarily divide this into segments of
maximum size 127 for Spread - is this sufficient? Or has this limit
been raised too / can I lift it?
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