By default, MySQL supports three engines: ISAM, MyISAM, and HEAP.The other two types are InnoDB and Berkley (BDB).

ISAM

ISAM is a well-defined and time-tested approach to managing data tables, designed with the database in mind that the number of times the database is queried is much greater than the number of updates.As a result, ISAM performs read operations very fast and does not consume a lot of memory and storage resources.The two main drawbacks of ISAM are that it doesn't support transactions, and it's not fault-tolerant: if your hard drive crashes, the data files can't be recovered.If you are using ISAM in a mission-critical application, you must frequently back up all your real-time data, and through its replication feature, MySQL can support such a backup application.

MyISAM

MyISAM is MySQL's ISAM extension format and default database engine.In addition to providing extensive functionality for index and field management not found in ISAM, MyISAM also uses a table locking mechanism to optimize multiple concurrent read and write operations.The price is that you need to run the OPTIMIZE TABLE command frequently to recover the space wasted by the update mechanism.MyISAM also has some useful extensions, such as the MyISAMChk tool to repair database files and the MyISAMPack tool to recover wasted space.

MyISAM emphasizes fast read operations, which is probably the main reason why MySQL is so favored by web development: a lot of data operations you do in web development are read operations.Therefore, most web hosting providers and Internet platform providers (Internet Presence Provider, IPP) only allow the use of MyISAM format.

HEAP

HEAP allows temporary tables that only reside in memory.Being in-memory makes HEAP faster than both ISAM and MyISAM, but the data it manages is volatile and all data is lost if not saved before shutdown.HEAP also doesn't waste a lot of space when rows are deleted.HEAP tables are useful when you need to use SELECT expressions to select and manipulate data.Remember to delete the form when you are done using it.Let me repeat it again: don't forget to delete the form after you're done using it.

InnoDB and Berkley DB

InnoDB and the Berkley DB (BDB) database engine are both direct products of the technology that enables MySQL's flexibility, the MySQL++ API.Almost every challenge you face when using MySQL stems from the fact that ISAM and the MyISAM database engine do not support transactions or foreign keys.Although much slower than the ISAM and MyISAM engines, InnoDB and BDB include support for transaction processing and foreign keys, both of which the previous two engines did not.As mentioned earlier, if your design requires one or both of these features, you are forced to use one of the latter two engines.