The discussion glosses over another important factor: the speed with which your pages are actually put together on your server. Most big modern websites store their information in a database and use a language such as PHP or ASP to extract it, turn it into HTML and send it to the Web browser.
So, even if you get your home page down to 1.5 seconds (Google’s threshold for being considered a “fast” website), you can still frustrate customers if your search page takes too much time to respond, or if the product pages load quickly but the “Customer reviews” delay for several seconds.
What Is A Database? What Is SQL?
A database is basically a collection of tables of information, such as a list of customers and their orders. It could be a filing cabinet, a bunch of spreadsheets, a Microsoft Access file or Amazon’s 40 terabytes of book and customer data.
A typical database for a blog has tables for users, categories, posts and comments. WordPress includes these and a few other starter tables. A typical database for an e-commerce website has tables for customers, products, categories, orders and order items (for the contents of shopping baskets). The open-source e-commerce software Magento includes these and many others. Databases have many other uses — such as for content management, customer relations, accounts and invoicing, and events — but these two common types (i.e. for a blog and an e-commerce website) will be referenced throughout this article.
Some tables in a database are connected to other tables. For example, a blog post can have many comments, and a customer can make multiple orders (these are one-to-many relationships). The most complicated type of database relationship is a many-to-many relationship. One relationship is at the core of all e-commerce databases: an order can contain many products, and a single product can be added to many different orders. This is where the “order items” table comes in: it sits between the products and the orders, and it records every time a product is added to an order. This will be relevant later on in the article, when we look at why some database queries are slow.
The word database also refers to the software that contains all this data, as in “My database crashed while I was having breakfast,” or “I really need to upgrade my database.” Popular database software include Microsoft Access 2010, Microsoft SQL Server, MySQL, PostgreSQL and Oracle Database 11g.
The acronym SQL comes up a lot when dealing with databases. It stands for “structured query language” and is pronounced “sequel” or “es-cue-el.” It’s the language used to ask and tell a database things — exciting things like SELECT lastname FROM customers WHERE city='Brighton'. This is called a database query because it queries the database for data. There are other types of database statements: INSERT for putting in new data, UPDATE for updating existing data, DELETE for deleting things, CREATE TABLE for creating tables, ALTER TABLE and many more.
How Can A Database Slow Down A Website?
A brand new empty website will run very fast, but as it grows and ages, you may notice some sluggishness on certain pages, particularly pages with complicated bits of functionality. Suppose you wanted to show “Customers who bought this product also bought…” at the bottom of a page of products. To extract this information from the database, you would need to do the following:
1. Start with the current product,
2. See how many times the product has recently been added to anyone’s shopping basket (the “order items” table from above),
3. Look at the orders related to those shopping baskets (for completed orders only),
4. Find the customers who made those orders,
5. Look at other orders made by those customers,
6. Look at the contents of those orders’ baskets (the “order items” again),
7. Look up the details of those products,
8. Identify the products that appear the most often and display them.
You could, in fact, do all of that in one massive database query, or you could split it up over several different queries. Either way, it might run very quickly when your database has 20 products, 12 customers, 18 orders and 67 order items (i.e. items in shopping baskets). But if it is not written and programmed efficiently, then it will be a lot slower with 500 products, 10,000 customers, 14,000 orders and 100,000 order items, and it will slow down the page.
This is a very complicated example, but it shows what kind of stuff goes on behind the scenes and why a seemingly innocuous bit of functionality can grind a website to a halt.
A website could slow down for many other reasons: the server running low on memory or disc space; another website on the same server consuming resources; the server sending out a lot of emails or churning away at some other task; a software, hardware or network fault; a misconfiguration. Or it may have suddenly become a popular website. The next two sections, therefore, will look at speed in more detail.