MySQL engine differences

The MySQL database engine depends on how MySQL was compiled when it was installed. To add a new engine, you must recompile MySQL. By default, MySQL supports three engines: ISAM, MyISAM, and heap. Two other types of InnoDB and Berkley (BDB) are also often available. If you're skilled, you can use MYSQL+API to make an engine yourself. Several database engines are described below:

ISAM: ISAM is a well-defined and time-tested method of data table management that, at design time, takes into account that the number of times the database is queried is much larger than the number of updates. SoISAM performs read operations quickly and does not consume a large amount of memory and storage resources. The two main disadvantages of ISAM are that it does not support transactional processing or fault tolerance: If your hard drive crashes, the data file cannot be recovered. If you are using ISAM in mission-critical applications, you must always back up all of your real-time data, and with its replication features, MySQL can support such a backup application.
MyISAM: MyISAM is the ISAM extended format for MySQL and the default database engine.In addition to providing a number of functions for index and field management not available in ISAM, MyISAM also uses a table-locking mechanism to optimize multiple concurrent read and write operations, at the expense of the need to run the Optimize Table command frequently to restore space wasted by the updated mechanism. MyISAM also has some useful extensions, such as the Myisamchk tool for repairing database files and the Myisampack tool for recovering wasted space.MyISAM emphasizes fast read operations, which may be the main reason why MySQL is so popular with Web development: in Web development, the bulk of your data operations are read operations. SoMYISAM format is the inability to recover data after a table is corrupted.
HEAP : HEAP allows temporary tables that reside only in memory. Residing in memory makes the heap faster than ISAM and MyISAM, but the data it manages is unstable, and if it is not saved before shutting down, all the data will be lost. The heap does not waste a lot of space when data rows are deleted. The heap table is useful when you need to select and manipulate data using a select expression.      InnoDB : InnoDB database engine is a direct product of the technology that makes MySQL flexible, and this technology is MYSQL+API. myisam differs from InnoDB
InnoDB and MyISAM are the two most common table types used by many people when using MySQL, both of which have pros and cons, depending on the application. The basic difference is that the MyISAM type does not support advanced processing such as transaction processing, and InnoDB type support. The MyISAM type of table emphasizes performance, which is performed more quickly than the InnoDB type, but does not provide transactional support, while InnoDB provides transactional support for advanced database functions such as external keys.

The following are some of the details and the specific implementation differences:
1.InnoDB does not support indexes of type Fulltext.
The exact number of rows in the table is not saved in 2.InnoDB, that is, when you execute select COUNT (*) fromtable, InnoDB scans the entire table to calculate how many rows, but MyISAM simply reads the saved rows. Note that when the COUNT (*) statement contains a where condition, the operation of the two tables is the same.
3. For a field of type auto_increment, InnoDB must contain only the index of that field, but in the MyISAM table, you can establish a federated index with other fields.
4.DELETE from table, InnoDB does not reestablish the table, but deletes one row at a time.
5.LOAD Table Frommaster operation does not work for InnoDB, the workaround is to first change the InnoDB table to a MyISAM table, import the data and then change it to a InnoDB table, but not for tables that use additional InnoDB features (such as foreign keys).

In addition, the row lock of the InnoDB table is not absolute, if MySQL cannot determine the scope to scan when executing an SQL statement, the InnoDB table also locks the full table, for example updatetable set num=1 where name like "a%"
The main difference between the two types is that InnoDB supports transactional and foreign key and row-level locks. MyISAM is not supported. So MyISAM tend to be considered only suitable for use in small projects.
I use MySQL as a user point of view, InnoDB and MyISAM are more like, but from my current operation of the database platform to meet the requirements: 99.9% stability, convenient scalability and high availability, MyISAM is definitely my first choice.

The reasons are as follows:
1, first of all, I am currently on the platform of the majority of projects are read more write less projects, and MyISAM reading performance is stronger than InnoDB.
2, MyISAM index and data are separate, and the index is compressed, the memory usage of the corresponding improved a lot. Can load more indexes, and InnoDB is the index and the data is tightly bound, do not use compression which will cause innodb than MyISAM volume is large.
3, from the platform point of view, often 1, 2 months will occur application developers accidentally update a table where the scope of the wrong, resulting in this table can not be normal use, this time MyISAM the superiority of the embodiment, casually from the day copy of the compressed package out of the corresponding table file, Put it in a database directory, then dump into SQL and back to the main library, and binlog the corresponding. If it's InnoDB, I'm afraid it can't be so fast, don't tell me to let InnoDB regularly back up with an export xxx.sql mechanism, because the smallest database instance on my platform has a size of dozens of g of data.
4, from my contact with the application logic, select COUNT (*) and order BY is the most frequent, probably can account for the entire SQL total statement of more than 60% of the operation, and this operation InnoDB actually will lock the table, many people think InnoDB is a row-level lock, That's just where the primary key is valid, and the non-primary key will lock the full table.
5, there is often a lot of application departments need me to give them regular data on some tables, MyISAM words are very convenient, as long as they correspond to the list of the frm. myd,myi files, let them in the corresponding version of the database to start the line, and InnoDB need to export xxx.sql, because the light to other people's files, by the dictionary data file, the other side is not available.
6, if and myisam than insert write operation, InnoDB also not up to MyISAM write performance, if is for index-based update operation, although MyISAM may be inferior innodb, but so high concurrency of write, from the library can chase is also a problem, It might as well be solved by a multi-instance sub-Library table architecture.
7, if it is used MyISAM, the merge engine can greatly speed up the development of the application department, they just do some selectcount (*) operation on this merge table, it is very suitable for a large project total of about hundreds of millions of rows of a type (such as journal, Survey statistics) business table.
Of course, InnoDB is not absolutely not, with business projects such as simulation stocks, I am using InnoDB, active users more than 200,000, is also very easy to cope with, so I personally also like InnoDB, but if from the database platform application, I still headman MyISAM.
In addition, some may say that you myisam can't resist too much write operation, but I can make up by the architecture, say a database platform that I use nowCapacity:The total number of master and slave data is more than hundreds of T, more than 1 billion PV dynamic page per day, there are several major items are called by the data interface method is not counted into PV total, (including a large project because the initial memcached is not deployed, resulting in a single database processing 90 million of queries per day). My overall database server load averaged around 0.5-1.

Generally speaking, MyISAM is suitable for:
(1) do a lot of count calculation;
(2) The insertion is not frequent, the query is very frequent;
(3) No business.

InnoDB Suitable for:
(1) Reliability requirements are relatively high, or require business;
(2) Table updates and queries are fairly frequent, and the chances of table locking are relatively large when specifying the creation of the data engine
The switch that makes all the flexibility possible is the MySQL extension--type parameter that is provided to ANSI SQL. MySQL allows you to specify the database engine at the level of the table, so they sometimes refer to table formats. The following example code shows how to create a table that uses the MyISAM, ISAM, and heap engines, respectively. Note that the code to create each table is the same, except for the last type parameter, which is used to specify the data engine.

MySQL engine differences