What are the differences between MyISAM and InnoDB?

Difference:

1. InnoDB support transactions, MyISAM is not supported, for INNODB each SQL language is encapsulated as a transaction by default, auto-commit, which affects speed, so it is better to put multiple SQL language between Begin and commit, compose a transaction;

2. InnoDB supports foreign keys, while MyISAM is not supported. The conversion of a InnoDB table containing a foreign key to MyISAM will fail;

3. InnoDB is a clustered index, the data file is tied to the index, must have a primary key, through the primary key index efficiency is very high. However, the secondary index requires two queries, first querying the primary key, and then querying the data through the primary key. Therefore, the primary key should not be too large, because the primary key is too large and the other indexes will be large. While MyISAM is a nonclustered index, the data file is detached and the index holds a pointer to the data file. The primary key index and the secondary index are independent.

4. InnoDB does not save the exact number of rows in the table, and a full table scan is required to execute SELECT COUNT (*) from table. and MyISAM with a variable to save the entire table row number, the execution of the above statement only need to read out the variable, fast;

5. InnoDB does not support full-text indexing, while MyISAM supports full-text indexing, and the query efficiency is MyISAM high;

How to choose:

1. Whether to support transactions, if you want to choose InnoDB, if you do not need to consider myisam;

2. If the majority of the table is just read query, you can consider MyISAM, if both read and write are very frequent, please use InnoDB.

3. After the system MyISAM, it is more difficult to recover, can accept;

4. MySQL5.5 version start InnoDB has become the default engine of MySQL (previously MyISAM), stating that its advantages are obvious, if you do not know what to use, then use InnoDB, at least not bad.

The difference in composition:

Each myisam is stored as three files on disk. The first file name begins with the name of the table, and the extension indicates the file type.

The. frm file stores the table definition.

The data file has an extension of. MYD (MYData).

The extension of the index file is. MYI (Myindex).

A disk-based resource is a InnoDB tablespace data file and its log file, and the size of the InnoDB table is limited only by the size of the operating system file, typically 2GB
transaction Processing Aspects :

Tables of the MyISAM type emphasize performance, which is performed more quickly than the InnoDB type, but does not provide transactional support

InnoDB provides transaction support transactions, external keys and other advanced database functions

SELECT Update,insert , Delete Operation
If executing a lot of select,myisam is a better choice

1. If your data performs a large number of inserts or UPDATE, for performance reasons, you should use the InnoDB table

2.DELETE from table , InnoDB does not reestablish the table, but deletes one row at a time.

3.LOAD table from MASTER operation does not work for InnoDB, the solution is to first change the InnoDB table to MyISAM table, import data and then change to InnoDB table, However, tables that use additional InnoDB attributes (such as foreign keys) do not apply

the auto_increment the Operation

The internal processing of one auto_incremen column per table.

MyISAM to be INSERT and the UPDATE The operation automatically updates this column . This makes the Auto_increment column faster (at least 10%). The value at the top of the sequence cannot be exploited after it has been deleted. (When the Auto_increment column is defined as the last column of a multicolumn index, the use of values removed from the top of the sequence can occur).

Auto_increment value can be reset by ALTER TABLE or MYISAMCH

For fields of type auto_increment, InnoDB must contain only the index of the field, but in the MyISAM table, you can establish a federated index with other fields

Better and faster auto_increment processing

If you specify a auto_increment column for a table, the InnoDB table handle in the data dictionary contains a counter called the autogrow counter, which is used to assign a new value to the column.

autogrow counters are stored only in main memory, not on disk

For the algorithm implementation of this calculator, please refer to the

auto_increment listed in InnoDB how to work in

The exact number of rows in the table
Select COUNT (*) from Table,myisam as long as you simply read the number of rows saved, note that when the COUNT (*) statement contains a where condition, the operation of the two tables is the same

The exact number of rows in a table is not saved in InnoDB, that is, when you execute select COUNT (*) from table, InnoDB scans the entire table to calculate how many rows

Lock
Table lock

Provides row lock (locking on row level), providing no lock read consistent with Oracle type (non-locking read in
Selects), in addition, the row lock of the InnoDB table is not absolute, and if MySQL cannot determine the range to scan when executing an SQL statement, the InnoDB table also locks the full table, such as the Update table set num=1 where name like "% aaa% "

What are the differences between MyISAM and InnoDB?