Tag Archives: Storage Engine

InnoDB Storage Engine

InnoDB is a transaction-safe storage engine for MySQL that has commit, rollback, and crash-recovery capabilities to protect user data. It stores user data in clustered indexes to reduce I/O for common queries based on primary keys. To maintain data integrity, InnoDB also supports FOREIGN KEY referential-integrity constraints.InnoDB has been designed for maximum performance when processing large data volumes. Its CPU efficiency is probably not matched by any other disk-based relational database engine.The InnoDB storage engine maintains its own buffer pool for caching data and indexes in main memory. InnoDB stores its tables and indexes in a tablespace, which may consist of several files .

InnoDB is used in production at numerous large database sites requiring high performance.

MyISAM Storage Engine

MyISAM is the default storage engine. It is based on the older ISAM storage engine with new extensions.
It manages nontransactional tables. It provides high-speed storage and retrieval, as well as fulltext searching capabilities
Each MyISAM table is stored on disk in three files. The files have names that begin with the table name and have an extension to indicate the file type. An .frm file stores the table format.
The data file has an .MYD (MYData) extension. The index file has an .MYI (MYIndex) extension.

Storage engine should be mentioned when we careate tables


Normally, it is unnecessary to use ENGINE to specify the MyISAM storage engine. MyISAM is the default engine unless the default has been changed. To ensure that MyISAM is used in situations where the default might have been changed, include the ENGINE option explicitly.

You can check or repair MyISAM tables with the mysqlcheck client or myisamchk utility.

All data values are stored with the low byte first. This makes the data machine and operating system independent.

All numeric key values are stored with the high byte first to permit better index compression.

Large files (up to 63-bit file length) are supported on file systems and operating systems that support large files.

There is a limit of 232  rows in a MyISAM table. If you build MySQL with the

The maximum number of indexes per MyISAM table is 64.

The maximum number of columns per index is 16.

The maximum key length is 1000 bytes.

When rows are inserted in sorted order ,the index tree is split so that the high node only contains one key. This improves space utilization in the index tree.

MyISAM supports concurrent inserts:

You can put the data file and index file in different directories on different physical devices

BLOB and TEXT columns can be indexed.

NULL values are permitted in indexed columns.

There is a flag in the MyISAM index file that indicates whether the table was closed correctly.

The sum of the lengths of the VARCHAR and CHAR columns in a table may be up to 64KB.


Storage Engines

A storage engine (database engine) is the underlying software component that a database management system (DBMS) uses to create, read, update and delete (CRUD) data from a database. Many of the modern DBMS support multiple database engines within the same database.Below given are the different storage engines that MySQL supports .