>
> My question is:
> Why would they deem it necessary to use yet a third server?   Could it
> be because the main server and the main slave are constantly being
> updated and they wouldn't want to overload the main slave(which
> is not on as high a horsepower of a box I know for a fact).  Could it
> be because maybe the subset of tables that they put on the third server
> are relatively more stable and hence there arent so many writethroughs
> so it can handle the complex selects better.
>
> All theories gladly accepted...
>
I'm not too sure about the third server either, but I do have an idea. It
wouldn't make much sense if the third server had different data on it. That
would tend to make things difficult to keep up to date - or maybe not. It
might be a slave that they only connect to the master every so often.

It's very common to have applications that write to one server and read from
a slave server. Sometimes many slave servers since there are typically way
more reads than writes.

Perhaps they use the third server so that if the master or slave servers die
there will always be a spare server for reads.

As far as any difference in the tables on the third server... Since it is
doing selects only you can start a slave server with a few options to speed
things up like:  --skip-innodb, --skip-bdb, --low-priority-updates,
and --delay-key-write=ALL which will force the server to use
non-transactional MyIsam tables for better performance.

It's really tough to speculate. Every system administrator would probably do
it a different way.

Jim Grill



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