MySQL Database Engine isam, MyISAM, heap

Reposted from: Workshop. If you want to, you can even use MySQL ++ API to create your own database engine, just like hitting the cylinder and installing your own carburetor. Now let's take a look at how you choose an engine and how to switch between available engines. Select your engine
The database engine you can use depends on how MySQL is compiled during installation. To add a new engine, you must recompile MySQL. The concept of compiling an application just to add a feature may be strange for Windows developers, but it has become a standard in the UNIX world. By default, MySQL supports three engines: ISAM, MyISAM, and HEAP. The other two types of InnoDB and Berkley (BDB) are also frequently used.

ISAM
ISAM is a well-defined and time-tested data table management method. It is designed to take into account that the number of database queries is much larger than the number of updates. Therefore, ISAM performs read operations quickly without occupying a large amount of memory and storage resources. The two major disadvantages of ISAM are that it does not support transaction processing or fault tolerance: If your hard disk crashes, data files cannot be recovered. If you are using ISAM in a key task application, you must always back up all your real-time data. With its copy feature, MySQL can support such backup applications.

MyISAM
MyISAM is the MySQL ISAM extension format and default database engine. In addition to providing a large number of functions for indexing and field management not available in ISAM, MyISAM also uses a table lock mechanism to optimize multiple concurrent read/write operations. The cost is that you need to run the optimize table command frequently to restore the space wasted by the update mechanism. MyISAM also has some useful extensions, such as the MyISAMChk tool used to fix database files and the MyISAMPack tool used to restore wasted space.

MyISAM emphasizes fast read operations, which may be the main reason why MySQL is so favored by Web development: In Web development, a large number of data operations you perform are read operations. Therefore, most VM providers and Internet platform providers (Internet Presence Provider, IPP) only allow the use of MyISAM format.

HEAP
HEAP allows only temporary tables in memory. HEAP is faster than ISAM and MyISAM in the memory, but the data it manages is unstable. If it is not saved before shutdown, all the data will be lost. When a row is deleted, HEAP does not waste much space. HEAP tables are useful when you need to use SELECT expressions to SELECT and manipulate data. Remember to delete the table after the table is used up. Let me repeat it again: do not forget to delete the table after you have used up the table.

InnoDB and Berkley DB
InnoDB and Berkley DB (BDB) database engines are both direct products that make MySQL flexible technology. This technology is MySQL ++ API. When using MySQL, almost every challenge you face comes from the fact that the ISAM and MyISAM database engines do not support transaction processing or foreign keys. Although it is much slower than ISAM and MyISAM engines, InnoDB and BDB include support for transaction processing and Foreign keys, both of which are not available in the first two engines. As mentioned above, if your design requires one or both of these features, you will be forced to use one of the two engines.

If you feel that you are indeed highly skilled, you can also use MySQL ++ to create your own database engine. This API provides you with the functions of operation fields, records, tables, databases, connections, and security accounts, as well as all the other numerous functions required to create DBMS such as MySQL. An in-depth explanation of the API is beyond the scope of this article, but you need to understand the existence of MySQL ++ and the technology behind the interchangeable engine. This is very important. It is estimated that the plug-in database engine model can even be used to create a local XML provider for MySQL ). (Any MySQL ++ developer reading this article may regard this as a requirement .) [Page]

Press Switch
The switch that makes all flexibility possible is to provide the MySQL extension-TYPE parameter for ansi SQL. MySQL allows you to specify the database engine at the table layer, so they sometimes referTable formats. The following sample code shows how to create tables using the MyISAM, ISAM, and HEAP engines. Note that the code for creating each table is the same except for the final TYPE parameter, which is used to specify the Data Engine.
 
Create table tblMyISAM (
Id int not null AUTO_INCREMENT,
Primary key (id ),
Value_a TINYINT
) TYPE = MyISAM
Create table tblISAM (
Id int not null AUTO_INCREMENT,
Primary key (id ),
Value_a TINYINT
) TYPE = ISAM
Create table tblHeap (
Id int not null AUTO_INCREMENT,
Primary key (id ),
Value_a TINYINT
) TYPE = Heap
 
You can also use the alter table command to move the original TABLE from one engine to another. The following code shows how to use alter table to move a MyISAM TABLE to the InnoDB engine:
 
Alter table tblMyISAM change type = InnoDB
 
MySQL uses three steps to achieve this goal. First, a copy of the table is created. Then, any changes to input data are queued, and the copy is moved to another engine. Finally, any changes made to data in the queue are sent to a new table, and the original table is deleted.

Alter table shortcuts
To update a table from ISAM to MyISAM, you can use Mysql_convert_table_format Command without the need to write the alter table expression