MySQL storage engines
In this chapter, we will talk about MySQL storage engines.
A storage engine is a software module that a database management system uses to create, read, update data from a database. There are two types of storage engines in MySQL. Transactional and non-transactional.
The default storage engine for MySQL prior to version 5.5 was MyISAM. For MySQL 5.5 and later, the default storage engine is InnoDB. Choosing the right storage engine is an important strategic decision, which will impact future development. In this tutorial, we will be using MyISAM, InnoDB, Memory and CSV storage engines. If you are new to MySQL and your are studying the MySQL database management system, then this is not much of a concern. If you are planning a production database, then things become more complicated.
List of storage engines
MySQL supported storage engines:
MyISAM is the original storage engine. It is a fast storage engine. It does not support transactions. MyISAM provides table-level locking. It is used most in Web, data warehousing.
InnoDB is the most widely used storage engine with transaction support. It is an ACID compliant storage engine. It supports row-level locking, crash recovery and multi-version concurrency control. It is the only engine which provides foreign key referential integrity constraint.
Memory storage engine creates tables in memory. It is the fastest engine. It provides table-level locking. It does not support transactions. Memory storage engine is ideal for creating temporary tables or quick lookups. The data is lost when the database is restarted.
CSV stores data in CSV files. It provides great flexibility, because data in this format is easily integrated into other applications.
Merge operates on underlying MyISAM tables. Merge tables help manage large volumes of data more easily. It logically groups a series of identical MyISAM tables, and references them as one object. Good for data warehousing environments.
Archive storage engine is optimised for high speed inserting. It compresses data as it is inserted. It does not support transactions. It is ideal for storing, retrieving large amounts of seldom referenced historical, archived data.
The Blackhole storage engine accepts but does not store data. Retrievals always return an empty set. The functionality can be used in distributed database design where data is automatically replicated, but not stored locally. This storage engine can be used to perform performance tests or other testing.
Federated storage engine offers the ability to separate MySQL servers to create one logical database from many physical servers. Queries on the local server are automatically executed on the remote (federated) tables. No data is stored on the local tables. It is good for distributed environments.
Choosing the right engine
No storage engine is ideal for all circumstances. Some perform best under certain conditions and perform worse in other situations. There are tradeoffs than must be considered. A more secure solution takes more resources. It might be slower, take more CPU time and disk space. MySQL is very flexible in the fact that it provides several different storage engines. Some of them, like the Archive engine, are created to be used in specific situations. Ironically this also brings a question, which storage engine to use? Which may not be easily answered.
In some cases, the answer is clear. Whenever we are dealing with some payment systems, we are obliged to use the most secure solution. We cannot afford to loose such sensitive data. InnoDB is the way to go. If we want full-text search, than we must choose MyISAM. Only InnoDB supports foreign key referential integrity constraint and if we plan to use this constraint, then the choice is clear. In many situations we must have enough experience to choose the right engine. And if we lack the experience, than the best way is to ask some seasoned developer. One of the best ways is to ask on specific Internet forums. stackoverflow.com is a great one. The question is further complicated by the fact that we can choose different storage engines for different tables.
Specifying and altering storage engines
The storage engine is specified at the time of the table creation.
mysql> CREATE TABLE Cars(Id INTEGER PRIMARY KEY, Name VARCHAR(50), -> Cost INTEGER) ENGINE='MyISAM';
ENGINE keyword specifies the storage engine used
for this particular table.
If we do not specify the storage engine explicitly, then the default storage engine is used. Prior to MySQL 5.5 the default storage engine was MyISAM. For MySQL 5.5 and later, the default storage engine is InnoDB.
mysql> SHOW VARIABLES LIKE 'storage_engine'; +----------------+--------+ | Variable_name | Value | +----------------+--------+ | storage_engine | InnoDB | +----------------+--------+ 1 row in set (0.00 sec)
The default storage engine can be found in the
It is possible to migrate to a different storage engine. Note that migrating a large table might take a long time. Also we might run into some problems when migrating tables. Some features might not be supported in both tables.
mysql> SELECT ENGINE FROM information_schema.TABLES -> WHERE TABLE_SCHEMA='mydb' -> AND TABLE_NAME='Cars'; +--------+ | ENGINE | +--------+ | InnoDB | +--------+ 1 row in set (0.00 sec)
This SQL statement finds out the storage engine used for a
Cars table in
mydb database. We could also use
SELECT CREATE TABLE Cars SQL statement. The
is a table which stores technical information about our tables.
mysql> ALTER TABLE Cars ENGINE='MyISAM';
This SQL statement changes the storage engine to MyISAM.
mysql> SELECT ENGINE FROM information_schema.TABLES -> WHERE TABLE_SCHEMA='mydb' -> AND TABLE_NAME='Cars'; +--------+ | ENGINE | +--------+ | MyISAM | +--------+ 1 row in set (0.00 sec)
Now the storage engine is MyISAM.
In this part of the MySQL tutorial, we have covered storage engines.