High Performance MySQL [Electronic resources] نسخه متنی

9.1 Why Backups?

Strangely, some people never
stop to consider why they need to back up their
servers. The data is important, so we just assume that backing it up
is equally important. That's good, because backups
are important and do need to be done. But by
understanding the various ways in which backups may be used, we gain
some perspective on the utility of various backup strategies.

9.1.1 Disaster Recovery

Disaster recovery is the most popular
motivation for running backups, but in reality it is often not as
relevant as some of the other reasons we'll look at.

What is a disaster? For our purposes, a disaster is any event that
causes significant portions of the data to be corrupted or
unavailable. Some examples of disasters include the following:

Hardware failure

Software failure

Accidental erasure of data^[2]

^[2] The day after writing this
section, Jeremy received a late phone call from a coworker who had
accidentally mistyped the WHERE clause in a
DELETE query. Luckily there was a good backup on
hand.

Stolen server

Physically destroyed server

Any of these disasters can occur at any time. The odds of any one of
them occurring are pretty low, but none of them are impossible.
Having a known good copy of your data on hand will greatly minimize
the pain of having to recover. It's a form of
insuranceand cheap insurance at that.

Some of these disasters might be the result of a natural disaster
(tornado, earthquake, mudslide, etc.). Unlike a simple disk failure,
nature's catastrophes have a habit of physically
damaging and even destroying entire buildings. To be truly safe, you
need to have off-site backups. Something as simple as taking the
tapes home with you every other week or sending a set to a remote
office may prove to be invaluable if nature strikes.

9.1.2 Auditing

There
are times when you'd like to be able to go back in
time and see what a database, table, or even a single record looked
like. Having older backups available makes this relatively easy to
do. Just pull out the correct files, load them onto a test server,
and run some queries. Depending on the type of data you store, there
may even be legal reasons why you need to keep old copies of your
data around.

Why else might you need the ability to go back in time and examine
older copies of your data? You might have to:

Look for data corruption

Decide how to fix a newly discovered bug retroactively

Compute the rate of growth for your databases

Provide evidence for a lawsuit or investigation

Of course, there are countless other situations in which older data
can be invaluable. The trouble is, you may not realize that until it
is too late.

9.1.3 Testing

It's
usually a good idea to test changes to an application before putting
them into production. To do that, you'll probably
have a separate database server you can load data onto to run various
tests. Over the course of development, you may need to wipe the data
clean and reload it several times.

If you have a recent backup of your production server available,
setting up a test server can be downright trivial. Just shut down
MySQL, restore the data, start MySQL, and begin testing.