n Thursday, October 30, 2003, at 12:19 pm, gianny DAMOUR wrote:
> Hello,
>
> Just a couple of questions regarding this design:
>
> - Is it possible to configure the weight of a node? If yes, is the
> same auto-partitioning policy applicable? My concern is that a
> "clockwise" policy may add a significant load on nodes hosted by low
> spec hosts.
This is partly a problem for the sticky load balancer to deal with i.e.
it should load requests to primary machines based on spec/power.
If we partitioned the session data into buckets (rather than one big
lump), then the buckets of session data can be distributed evenly
around the cluster so that each session bucket has N buddies (replicas)
but that a load-balancing algorithm could be used to distribute the
buckets based on (say) a host spec weighting or whatnot. e.g. nodes in
the cluster could limit how many buckets to accept due to their lack of
resources etc.
Imagine having 1 massive box and 2 small ones in a cluster - you'd
probably want to give the big box more buckets than the smaller ones.
The previous model Jules described still holds (that was a view of 1
session bucket) - its just that the total session state for a machine
might be spread over many buckets.
Having multiple buckets could also help spread the load of recovering
from a node failure in larger clusters.
>
> - I have the feeling that one can not configure a preferred
> replication group for primary sessions of a specific node: if four
> nodes are available, I would like to configure that sessions of the
> first node should be replicated by the third node, if available, or
> the fourth one.
>
> - Is it not an overhead to have b-1 replica? AFAIK, a single secondary
> should be enough.
It all depends on your risk profile I suppose. I backup is usually
enough but you may want 2 for extra resilience - especially as one of
those could be in a separate DR zone for really serious fail-over
scenarios.
James
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