Tuesday, November 2, 2010

locality of reference -- why

When data volume threatens latency, why is it important to /host/ application and its required data physically close? Why LoR?

J4: fewer hops on traceroute.
J4: network bandwidth is shared. Look at email traffic. Most GS emails travel only inside GS intranet, and don't add load to email gateways.
J4: ethernet is collision-sensitive. When ethernet is saturated, performance degrades. LoR reduces satuation.
J4: the backbone link between 2 "email gateways" tend to be an expensive and limited resource, so the less you use it, the more you can save on equipment and bandwidth lease.

In low-latency systems, it's best to avoid distributed cache. Use a single-JVM design to eliminate all serialization costs. Probably 2 orders of magnitude faster.

If all the required data by a particular application is physically close by (ideally single-jvm) then less serialization, less replication, less I/O stream synchronization (thread-unsafe by default)...

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