What is the difference between innodb and myisam in mysql?

Difference: 1. MyISAM does not support transactions, but InnoDB does. 2. InnoDB supports data row locking, while MyISAM does not support row locking and only supports locking the entire table. 3. InnoDB supports foreign keys, but MyISAM does not. 4. The primary key range of InnoDB is larger, up to 2 times that of MyISAM.

The difference between MyISAM and InnoDB

MySQL uses MyISAM by default.

MyISAM does not support transactions, but InnoDB does. InnoDB's AUTOCOMMIT is turned on by default, that is, each SQL statement will be encapsulated into a transaction by default and automatically submitted. This will affect the speed, so it is best to display multiple SQL statements between begin and commit to form a transaction. Go submit.

InnoDB supports data row locking, while MyISAM does not support row locking and only supports locking the entire table. That is, read locks and write locks on the same MyISAM table are mutually exclusive. When MyISAM concurrently reads and writes, if there are both read requests and write requests in the waiting queue, the default write request has a higher priority, even if the read request arrives first, so MyISAM is not suitable for situations where a large number of queries and modifications coexist, as the query process will be blocked for a long time. Because MyISAM is a lock table, a time-consuming read operation will starve other writing processes.

InnoDB supports foreign keys, but MyISAM does not.

The primary key range of InnoDB is larger, up to 2 times that of MyISAM.

InnoDB does not support full-text indexing, but MyISAM does. Full-text indexing refers to establishing an inverse sorted index for each word in char, varchar, and text (except stop words). MyISAM's full-text index is actually useless because it does not support Chinese word segmentation. The user must add spaces after word segmentation and then write it into the data table. Moreover, words with less than 4 Chinese characters will be ignored like stop words.

MyISAM supports GIS data, but InnoDB does not. That is, MyISAM supports the following spatial data objects: Point, Line, Polygon, Surface, etc.

Count(*) without where uses MyISAM much faster than InnoDB. Because MyISAM has a built-in counter, it reads directly from the counter when counting(*), while InnoDB must scan the entire table. Therefore, when executing count(*) on InnoDB, it is generally accompanied by where, and where must contain index columns other than the primary key. Why is there a special emphasis on "other than the primary key" here? Because the primary index in InnoDB is stored together with the raw data, while the secondary index is stored separately, and then there is a pointer pointing to the primary key. Therefore, if it is just count(*), it is faster to use the secondary index to scan, while the primary key is mainly used to scan the index and return raw data at the same time.

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