MySQLD B Engines

By Khushbu Varshney

One of the greatest things about MySQL, other than being free, widely supported and fast, is the flexibility of choosing different storage engines for different tables.MySQL comes with various storage enginesEvery storage engine is completely different, designed

to address a unique application needNot being locked down to a single storage engine (like

Oracle), means you can optimize and choose the best

tool for the jobMySQL storage engines include both those that handle

transaction-safe tables and those that handle

nontransaction-safe tables

MySQL DBEngines

Transaction-safe tables (TSTs) have several advantages over nontransaction-safe tables (NTSTs):

They are safer. Even if MySQL crashes or you get hardware problems, you

can get your data back, either by automatic recovery or from a backup

plus the transaction log.You can combine many statements and accept them all at the same time

with the COMMIT statement (if autocommit is disabled).You can execute ROLLBACK to ignore your changes (if autocommit is

disabled).If an update fails, all of your changes are reverted. (With nontransaction-

safe tables, all changes that have taken place are permanent.)Transaction-safe storage engines can provide better concurrency for

tables that get many updates concurrently with reads.

MySQL DBEngines

MyISAMInnoDBMERGEMEMORY (HEAP)BDB (Berkeley DB)FEDERATED ARCHIVECSVBLACKHOLE

Show Engine will show all of the supportive engine

provided by your DB

MySQL DBEngines

mysql> SHOW ENGINES\G*************************** 1. row *************************** Engine: MyISAMSupport: DEFAULTComment: Default engine as of MySQL 3.23 with great performance*************************** 2. row *************************** Engine: MEMORYSupport: YESComment: Hash based, stored in memory, useful for temporary tables*************************** 3. row *************************** Engine: InnoDBSupport: YESComment: Supports transactions, row-level locking, and foreign keys*************************** 4. row *************************** Engine: BerkeleyDBSupport: NOComment: Supports transactions and page-level locking*************************** 5. row *************************** Engine: BLACKHOLESupport: YESComment: /dev/null storage engine (anything you write to it disappears)

You can set the default storage engine to be used during the current session by setting the storage_engine or table_type variable:

SET storage_engine=MYISAM;SET table_type=BDB;

ISAM

ISAM is a well-defined, time-tested method of managing data tables, designed with

the idea that a database will be queried far more often than it will be updated.

ISAM performs very fast read operations and is very easy on memory and storage

resources.

The two main downsides of ISAM are that it doesn't support transactions and isn't

fault-tolerant: If your hard drive crashes, the data files will not be recoverable.

MyISAM

MyISAM is MySQL's extended ISAM format and default database engine. In addition

to providing a MyISAM uses a table-locking mechanism to optimize multiple

simultaneous reads and writes. MyISAM also has a few useful extensions such as the

MyISAMChk utility to repair database files and the MyISAMPack utility for

recovering wasted space.

MyISAM, with its emphasis on speedy read operations, is probably the major reason

MySQL is so popular for Web development, . As a result, most hosting and Internet

Presence Provider (IPP) companies will allow the use of only the MyISAM format.

MySQL DBEngines

MyISAM manages nontransactional tables. It provides

high-speed storage and retrieval, as well as fulltext

searching capabilities. MyISAM is supported in all

MySQL configurations, and is the default storage engine

unless you have configured MySQL to use a different

one by default.

Offers great performance for read heavy applications.

Most web services and data warehousing applications

use MyISAM heavily.

MySQL DBEngines

Important notes about MyISAM tables:

1. Your tables will get corrupted eventually! Plan accordingly.

2. Turn on auto-repair by adding this flag to your my.cnf file:

myisam-recover=backup,force

3. Super fast for read (select) operations.

4. Concurrent writes lock the entire table. Switch everything to

offline processing where you can, to serialize writes without taking

the database down. (Offline processing is golden and applies to all

table types)

MySQL DBEngines

CREATE TABLE tblMyISAM ( id INT NOT NULL AUTO_INCREMENT, PRIMARY KEY (id), value_a TINYINT) TYPE=MyISAM or ENGINE=MyISAM

CREATE TABLE tblISAM ( id INT NOT NULL AUTO_INCREMENT, PRIMARY KEY (id), value_a TINYINT) TYPE=ISAM or ENGINE=MyISAM

Memory or HEAP: The MEMORY storage engine provides in-memory tables. HEAP allows for temporary tables that reside only in memory. Residing in memory makes HEAP faster than ISAM or MyISAM, but the data it manages is volatile and will be lost if it's not saved prior to shutdown. HEAP also doesn’t waste as much space when rows are deleted. HEAP tables are very useful in situations where you might use a nested SELECT statement to select and manipulate data. Just remember to destroy the table after you’re done with it.

Note

The MEMORY storage engine formerly was known as the

HEAP engine.

MySQL DBEngines

While this type of table offers super fast retrieval, it only works well for small temporary tables.

If you try to load too much data into a Memory table,

MySQL will start swapping information to disk and then

you lose the benefits of an all-memory storage

MySQL DBEngines

The InnoDB and BDB storage engines provide transaction-safe tables. To maintain data integrity, InnoDB also supports FOREIGN KEY referential-integrity constraints.

Although much slower than the ISAM and MyISAM

engines, InnoDB and BDB include the transactional and

foreign-key support missing from the former two

choices. As such, if your design requires either or both

of these features, you’re actually compelled to use one

of these two choices

MySQL DBEngines

Important notes about InnoDB tables:

1. ACID transactions support. Row-level locking (compared to table level

locking with MyISAM) means faster concurrent writes.

2. Doing a "SELECT Count(*) FROM table" without specifying any indexes is

very slow on InnoDB and requires a full table scan. (With MyIsam this

operation doesn't cost anything because MyIsam stores an internal record

counter with each table).

If you need to "SELECT COUNT(*)" often on InnoDB tables, create MySQL

insert/delete triggers that will increment/decrement a counter whenever

records are added or deleted from the table.

MySQL DBEngines

3. Backup:

MySQLDump backup is too slow with InnoDB.

4. InnoDB has built-in recovery that works 99% of the times automatically. Never try to

move .frm or .ibd files around as a way of "helping" the database to recover.

5. InnoDB is less forgiving than MyIsam when it comes to queries on non indexes.

InnoDB is going to "School" you into ensuring every single query and update statement

runs on an index. Issue no index queries and you'll pay dearly in execution time.

6. Never ever change my.cnf INnoDB log file size while the database is running. You'll

corrupt the log sequence number beyond repair.

The ARCHIVE storage engine is used for storing large amounts of data without indexes with a very small footprint.

The CSV storage engine stores data in text files using comma-separated

values format.

The BLACKHOLE storage engine accepts but does not store data and

retrievals always return an empty set.

The FEDERATED storage engine was added in MySQL 5.0.3. This engine

stores data in a remote database. Currently, it works with MySQL only,

using the MySQL C Client API. In future releases, we intend to enable it to

connect to other data sources using other drivers or client connection

methods.

MySQL DBEngines

Examples:

Below are some examples of using the best storage engine for different tasks:

Web stats logging - Flat file for the logging with an offline processing demon processing and writing all stats into InnoDB tables.

Financial Transactions - InnoDB

Session data - MyISAM

Localized calculations - HEAP

Dictionary - MyISAM