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A Database Machine consists of two sets of Linux machines. There’s one set of Linux
machines that we call compute nodes, and these have masses of CPU, masses of RAM, and they
run your database instances.
There’s a second set of Linux machines that have a vast amount of disk space. These are
your storage tier, and it’s the Exadata software
that links the compute nodes to the cell nodes, the cell
nodes of the storage machines. Now, you cannot install the Exadata software
independently. It comes pre-installed on your DB
machine. I think, with earlier releases, it was possible to license Exadata software independently
and install it on your own box, but certainly with the current release, you cannot get it
unless you buy a DB machine.
Well, what does Exadata deliver? It delivers certain capabilities that you cannot get in
any other environments, and these are the abilities
that we’ll be studying in the next few slides. The Smart
Scan, that’s the one that gets all the publicity. It’s the ability to offload a large amount
of the SQL processing from the database tier from
the compute nodes to the storage tier to the cell
nodes. You have a storage tier that is aware of the database and can take over some of
the workload of executing your SQL.2
Then there’s Hybrid Columnar Compression. Strictly speaking, that is not unique to Exadata.
You can now use HCC if you have ZFS* or pillar storage, but it was developed for Exadata,
and use of HCC is critical to getting full value
from your Database Machine installation. Storage indexes, these are a technique for
making your full table scans even more efficient than
they were before, another way of evaluation predicates. Again, the predicate evaluation
is done on the cell nodes, not in the database tier.
Then there’s a Smart Flash Cache. The Smart Flash Cache wasn’t around in the earliest
releases of the Database Machine. This is what really
gives you the value for OLTP operations. People used to claim that Database Machine was wonderful
for the warehouse but not good for OLTP. Well, if that was ever true, which I would
dispute, the introduction of the Smart Flash Cache
certainly means it’s no longer true now. Lastly, I/O Resource Manager: this is important
because of the size of the Database Machine. Many sites will be using the Database Machine
for database and server consolidation and if you
are running 20 or 30 databases on one box, you need to be absolutely certain that one
database is not going to impact on another.
The I/O Resource Management capability allows you to set up resource management within the
database instances in the compute nodes and push those priorities down to the storage
tier so the cells themselves are aware that certain databases
must never have performance degradation no matter what the workload is on other databases.3
Well, these facilities are all very good, but experience shows that these features may
be a little more elusive than you might expect and it
can be very difficult and require a lot of work to make
sure that you really do get the value you deserve from installing the machine.