MySQL MyISAM Storage Engine
Overview
In this tutorial, we will learn about MyISAM Storage Engine. MyISAM was the default storage engine for older MySQL versions until it was replaced by InnoDB in MySQL 5.x.
MyISAM Storage Engine
MyISAM storage engine is based on Indexed Sequential Access Method(ISAM) indexing algorithm that retrieves information from large sets of data in a fast manner.
MyISAM is a non-transactional engine, light with high-speed performance, portable easy to copy between
systems and has a small data footprint. The MyISAM storage engine manages tables that have the following characteristics:
Represents each table using multiples files like :
- A data file(.myd) that stores the contents of table rows.
- An index file(.myi) that stores any indexes on the table.
Tables can be converted into fast, compressed, read-only tables to save space.
The table storage format is portable, so table files can be copied directly to another host.
We can specify preference of number of rows that a table should hold (minimum or maximum)
Storage Formats
The MyISAM storage engine supports three different table storage formats
- FIXED Format
- DYNAMIC Format
- COMPRESSED Format
FIXED format
All rows have the same size.
Rows are stored within the table at positions that are multiples of the row size, for easy to look up.
Fixed-size rows take more space.
DYNAMIC format
Rows take varying amounts of space.
Rows cannot be looked up as efficiently.
Dynamic-rows tables usually take less space because rows are not padded to a fixed size.
Fragmentation can occur more easily than for fixed- row tables.
COMPRESSED format
Tables are packed to save space.
Storage is optimized for quick retrieval.
Tables are read-only.
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