You Probably Don’t Need RAC
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2010-04-16
12:13:12
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You Probably Don’t Need RAC
If you’ve been holidaying in Siberia or similar places for about a year, you have
probably not talked to an Oracle Sales rep yet about RAC. But you will no doubt find
that there’s a voice mail waiting for you when you turn your mobile phone on again
after returning home from the vacation.
RAC is being pushed very hard by Oracle. You will get high availability, incredible
scalability, a much improved personal life, the ability to partition workloads, buy
cheap Linux servers and what have you.
It sounds pretty good. How can anyone say no to that kind of offer?
RAC is not OPS
No, RAC is not OPS, but it looks a lot like it. Oracle Marketing tries really hard to
distance RAC from OPS, and I don’t understand why. I mean: If the basic code has
been around for many years it means it’s stable, debugged and tried. If it’s all new,
who dares install it in a critical system? Fortunately, it’s not true that RAC is not
OPS. The basic parts of the code – GES and GCS – are pretty much the same as
they’ve always been.
GES stands for Global Enqueue Service and GCS stands for Global Cache Service.
More about that later.
A little history: OPS was created for version 6 of Oracle. The only clusters around
then were VAX/VMS clusters, but unfortunately the VAX/VMS Distributed Lock
Manager (DLM) was created originally to handle the coordination of relatively few
resources, such as files and devices, not 1000s of buffers in a buffer cache (Oracle or
others). It proved way too slow for OPS.
So Oracle had to create their own DLM for VAX/VMS, which they did. It took a
while, though, so it wasn’t until 6.0.35 (which was called “6.2” to celebrate the OPS
feature) that it finally came out.
I remember taking one of the first OPS classes (in Chicago) shortly after joining
Oracle and thinking that Oracle Development had gone mad – creating their own
DLM instead of letting the Digital guys do it (they had, after all, created the clusters
and the whole concept).
I was wrong. Oracle’s own DLM worked very well, and Digital adopted Oracle’s
technology and ideas in their own DLM, so when version 7 of Oracle came out, it was
again Digitals native DLM that was used.
The UNIX vendors then started doing Clusters (well, NCR had done it for a while).
And they mostly got the DLM technology from Oracle.
Microsoft certainly didn’t get their DLM technology from Oracle when they started
making Windows clusters. Oh no. They got it from Digital .
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