01-scaling-across-cores

Introduction
------------
The general issue is how to insure that the resolver scales.

Currently resolvers are CPU bound, and it seems likely that both
instructions-per-cycle and CPU frequency will not increase radically,
scaling will need to be across multiple cores.

How can we best scale a recursive resolver across multiple cores?

Some possible solutions:

a. Multiple processes with independent caches
b. Multiple processes with shared cache
c. A mix of independent/shared cache
d. Thread variations of the above

All of these may be complicated by NUMA architectures (with
faster/slower access to specific RAM).

How does resolution look like:

                               Receive the query. @# <------------------------\
                                       |                                      |
                                       |                                      |
                                       v                                      |
                                 Parse it, etc. $                             |
                                       |                                      |
                                       |                                      |
                                       v                                      |
                              Look into the cache. $#                         |
       Cry  <---- No <---------- Is it there? -----------> Yes ---------\     |
        |                            ^                                  |     |
 Prepare upstream query $            |                                  |     |
        |                            |                                  |     |
        v                            |                                  |     |
  Send an upstream query (#)         |                                  |     |
        |                            |                                  |     |
        |                            |                                  |     |
        v                            |                                  |     |
    Wait for answer @(#)             |                                  |     |
        |                            |                                  |     |
        v                            |                                  |     |
       Parse $                       |                                  |     |
        |                            |                                  |     |
        v                            |                                  |     |
   Is it enough? $ ----> No ---------/                                  |     |
        |                                                               |     |
       Yes                                                              |     |
        |                                                               |     |
        \-----------------------> Build answer $ <----------------------/     |
                                        |                                     |
                                        |                                     |
                                        v                                     |
                                   Send answer # -----------------------------/

Legend:
 * $ - CPU intensive
 * @ - Waiting for external event
 * # - Possible interaction with other tasks