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Oracle Tips by Burleson |
Preparing to Migrate
Invariably, other “experts” (using the term
loosely) and I will be asked hundreds of questions about
installation and migration to Oracle that could have been answered
if the people asking the questions had read the documentation and
tested new features before implementation. The point is, you have to
take the time to study the new features sections of the manuals,
read the readme.doc, and review utility scripts for “hidden”
changes.
Back when the Oracle8 migration was the
rage, I mentioned the compatible parameter in one of my columns. A
couple of weeks later, Oracle announced a spate of bugs that related
to the parameter. Were the two related? Probably. It demonstrated
that people who thought they had “migrated” to a new version of
Oraclehadn’t. Why? Because of the setting of the parameter, they
hadn’t even tested the new features that depended on a new redo log
format! Reading the documentation before they migrated would have
prevented this.
How about the person who buys one of those
great new sport utility vehicles only to discover it won’t fit in
their garage? Obviously, they didn’t check available resources
before “migrating” to a new vehicle. Oracle will take up to 150
percent more space for initial load than Oracle8 and up to three
times the space of Oracle 7.3. Do you have enough free space? You
may want to run both an Oracle and an Oracle8i (or earlier
release) system in parallel. Do you have enough memory (9i may
require twice to three times as much memory as previous releases
(512 megabytes on Linux, for example) or enough CPU? You will
require at least 50 meg of free space in an 8i SYSTEM tablespace to
upgrade to 9i, or the upgrade will fail. You may also want to take
note that the default installation of an Oracle database contains
a SYSTEM tablespace that is near 350 megabytes in size with only 40
Kilobytes free, you should plan your sizing accordingly.
Getting back to our geese versus lemmings
migration analogy: Which chose the better migration path
(overlooking hunters in this case…)? Don’t begin your migration
without a clear plan of how to get from your Oracle8i or earlier
instance to your Oracle instance. Decide on your path, preferably
one that doesn’t lead you over a cliff! Review the possible methods
to migrate your system; choose the best for your situation, and then
plan, plan, plan! In Oracle migration, you have the choice between
export and import, the Data Migration GUI tool, and the migration
command-line utility. Of course, there is also the CTAS method, but
that is only applicable to real S-and-M fanatics. In a 6.x version
database, you must first migrate to Oracle7.3.x and then migrate the
7.3.x database into 9i. In a 7.3.x to 9i, all of the methods are
applicable; however, in an 8.1.x to 9i, only the Data Migration
Assistant, export and import, unload, and SQLLOADER or CTAS are
available. Figures 1.22 through 1.25 show these migration paths.
See Code Depot
www.oracle-script.com |
