Data storage: the difference between MySQL InnoDB and MyISAM

storage

        InnoDB use frm Definition of file storage table 、ibd Store data and index .

        Mysql8.0 Before ：

                MyISAM use 3 Files to store data ,frm Definition of file storage table 、MYD Files store data 、MYI File storage index .

        Mysql8.0：

                MySQL8 Started deleting the original frm file , And USES the Serialized Dictionary Information (SDI), yes MySQL8.0 A new product introduced after redesigning the data dictionary , And has been used uniformly InnoDB The storage engine stores the metadata information of the table .SDI Information source records are kept in ibd In file .SDI With JSON Format store

                MyISAM use sdi Definition of storage table 、MYD Files store data 、MYI File storage index .

Functional aspects

        1.InnoDB Support transactions ,MyISAM I won't support it . because MyISAM Unsupported transaction , More secure transaction operations MyISAM More emphasis on performance , Therefore, the query efficiency will be higher than InnoDB Higher .

        2.InnoDB Support foreign keys ,MyISAM I won't support it . A containing foreign keys InnoDB turn MyISAM Will fail .

        3.InnoDB It's a clustered index ,MyISAM It's a non clustered index .InnoDB The primary key index of is a clustered index ,InnoDB You must have a primary key .

If the primary key is not explicitly defined when the table is created , be InnoDB The storage engine selects or creates a primary key as follows :

1 First, determine whether there is a non empty unique index in the table , If there is , Then the column is the primary key

2 If the above conditions are not met ,InnoDB The storage engine automatically creates a 6 Byte size primary key ( The user is not visible )

        4.InnoDB Do not save the specific rows of the table , perform select count(*) from table You need a full scan .MyISAM The number of records in the entire table is saved in one variable , When querying, you only need to get it out , fast .

        5.InnoDB Table level lock and row level lock are supported , and MyISAM Only table level locks are supported .