In the previous article I discussed using Read Replication Clustering to scale out reads for a website. What I will now do is describe a refined approach to the problem of scaling by creating "Application Clusters with Replication".

A common approach to website design is that a web designer creates a website and decides that search is a feature that they want to implement. If they use the MyISAM engine this means that they can add fulltext indexes to their tables and then make use of them in queries. I will ignore the case where the developer decides that an unanchored LIKE clause is an appropriate solution, since this developer will quickly hit a wall on performance and will need to learn what a fulltext index is.

So the developer adds a fulltext and is good to go? Sounds like an easy solution?

If the site the developer has written begins to see significant traffic





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If there is a common method of scaling with MySQL databases it is the
Read Replication Cluster solution.

Most websites start out with a single database and grow from there.
If the site's content is being generated from their database then
they will eventually hit a wall with reads from the database. Tuning
and hardware will buy you some growth but in the end disks spin only
so quickly. Luckily most websites are predominantly read intensive
and for this reason replication will solve scaling problems for many
people. Replication is a means by which MySQL sends updates of one
database to one or more databases which will act as a slave. These
changes are atomic, which means the changes are applied in full. No
row will ever be partially updated, and no transaction will be seen
on the slave that did not commit on the master












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I've never been all that interested in solving small problems. Small problems with scaling are resolved with single indexes, upgrades to hardware, or simply creating a bigger pipe.

When the measure of the Internet was a T-1, you could flood the network with the average 486. At the time I watched people buy hardware in the hundred's of thousands, and sometimes more, which never went used. Today's hardware is overkill for a lot of applications, so the first step in scaling is often tuning the hardware that you have already purchased. Make use of what you already have.

The "Slashdot Effect" is a perfect example of what is normally a small problem. What is the Slashdot Effect? Point tens of thousands of eyeballs at a website and watch it crash. The root cause of this? Most of the time it is because the site operator had their Apache max connections set to some ridiculous number.



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