This lesson will be a partial review for people who have gone through the developer courses but I still think it's important that we talk a little bit about storage engines here as we're talking about features of the MySQL server because it's such an important one. As a matter of fact the very fact that we can have multiple storage engines in MySQL distinguishes MySQL from every other database management system out there. So what is some basic things about the storage engines that we need to know. Well one of the first things is that in version 5.5 of MySQL the storage engines are now all plug-ins. So that means that if we need to remove one from our system so that we can free up some RAM for a storage engine that we're never going to use then we can do that simply by uninstalling that plug-in. That's a nice thing and if we find a third party storage engine that we want to incorporate, we no longer have to compile it into our MySQL server into a special compilation for ourselves. We can simply introduce it as a plug-in. So that's a nice thing. There are many features of the MySQL server that are storage engine dependent. So different storage engines will do those things in different ways. One of those is transaction support. That's not something that's overall in MySQL. As a matter of fact in our default installation only the InnoDB storage engine provides transaction support. So it's the only one that knows how to commit and especially how to rollback. The level at which we can perform locking also varies from engine to another. Most engines can do table level locking. However, in the default installation of MySQL, only the InnoDB engine can do row level locking and there's an older storage engine that we no longer put into our copy of MySQL called the BDB or the Berkeley Database Engine, that did page level locking but not row level locking. A page is like a collection of rows. The storage medium can vary from one engine to another. Most of our engines store their data on disk. However, the memory engine stores things in RAM. So it has no physical presence on the machine. If the server software MySQL D goes down, if we just stop the server or if we have a crash of some kind then all of the data in all of our memory tables is gone. So we want to be careful about that. There are ways of dealing with that and we'll talk about those in due course. The NDB engine expects it's data to be stored in a cluster somewhere that this MySQL server is accessing. So it's called an NDB cluster as a matter of fact, NDB is a whole technology. So there's a different kinds of storage media that we might be addressing. Data type and index type support is another thing that varies from one storage engine to another. So for example the memory engine doesn't support the long string data types, text or blog types at all. The MyISAM engine supports geospacial indexing and full text indexing but the InnoDB engine doesn't, nor does the memory engine or a bunch of the other ones. And some engines will also claim to support a specific data type but then will convert that to a different kind of data internally. So for example the memory engine will accept a variable character column but it will turn it into a character column even if it's more than 255 characters wide. Just so you know. And finally the caching of data in indexes will vary from one to the other and the very storage of the data and indexes will vary from one engine to another. Okay. Let's quickly look at what some of the common storage engines are, people who are already in the developer course know these things. MyISAM is the core engine of everything. It's the one that runs the show. It's the one that manages all the tables in the MySQL database which is the main administrative database in the MySQL server. It's the one that houses all the user accounts all the stored procedures and stored functions, a lot of different things are just stored in there in the MySQL database. It's also the one that the MySQL server uses for setting up implicit temporary tables, temporary tables that are used as part of the execution of some statement, those are all set up as MyISAM tables. InnoDB on the other hand is now the official default database. It used to be that the configuration file came with MySQL server with InnoDB set up to be the default database. But if we took that line out of the configuration file, the real default database storage engine was MyISAM. Not anymore. Without putting anything in the configuration file the InnoDB engine is now the default storage engine for MySQL in 5.5. It offers transaction support, row level locking, foreign key constraints and some other interesting things. The memory engine is just flat out fast. It's faster than anything else out there and it's used internally for a lot of things too. So when a person logs in, their login information is stored in memory table. As a matter of fact there are a lot of things from the MySQL database that are elevated to memory tables for the duration of the running of the server. User accounts and privileges are just one of those things but there are some other things as well and we will discuss those things as we go along. So it's all RAM based except for it's schema. So the format file for the memory table is still stored on disk so that we know how to reestablish that memory file again. And the other thing to know about the engines that you would, might not know if you weren't in the developer course, is that engines are assigned to tables on a table by table basis. We don't just say, "Well we're just going to use the InnoDB engine." We have to specify each table as being an InnoDB table and sometimes that's not the best choice. So we do have choice in the matter, we do have the ability to set a storage engine somewhat permanently as the engine that manages a specific table. Alright. So much on storage engines for now. We have an entire chapter a few chapters from now on storage engines where we go into a lot more detail about a lot of the features of each of them. The next thing I'd like to address is the information schema, that's going to be the subject of the next lesson.
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