Re: [Nolug] Quick question on clustering...

Ron can probably answer this better, but I'll take a stab at it.

Many times, the web server is physically separated from the database, so that
one machine doesn't have to do the work of processing requests from the user
(what link did the user click on, etc.), rendering pages, and hosting the
database application. If the database work is shuffled off to a separate
database server, this lightens the load on the webserver. Obviously you would
want the webserver and database server links to be very fast, possibly using
gigabit ethernet. You can then easily load-balance several web servers, all
pulling data from the database.

What about a cluster of database servers? Perhaps Ron can jump in here, but
if most of your database requests are selects or reads, then you can probably
replicate your data at intervals to several slave machines, while your writes
to the database would be sent to the master database, and these changes would
propagate to the slaves during scheduled replications.

Ron was telling me the other day about SAN (storage-attached networks), where
the database servers were networked together not by ethernet, but by scsi or
some other data connection to the storage media. This layout is kind of like
a bicycle tire, where the storage media is at the hub, and the database
servers are on the perimeter. They all share the same hard drive cluster
(RAID) for their reads and writes, therefore eliminating the need for the
staggered scheme detailed above. Replication in this instance would only be
needed for backup purposes.

Disclaimer: I haven't done any real database work, nor any high-load stuff,
but am only echoing what I've picked up over the years here and there. Also I
wrote a research paper on distributed databases for a client once which Scott
might remember reading.

--Joey

Thou spake:
>Craig Jackson <craig.jackson@wild.net> writes:
>> But maybe the answer isn't so quick ;)
>>
>> How is it that web servers can be clustered? How are the databases kept
>> in sync?
>
>Well that's two different issues isn't it? Or perhaps you need to
>provide a more detailed question....

-- 
Joey Kelly
< Minister of the Gospel | Computer Networking Consultant >
http://joeykelly.net
I'd rather crash a Ford than wreck a Chevy
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