mysql 数据库引擎

Alternative Storage Engines

Table of Contents

15.1 Setting the Storage Engine15.2 The MyISAM Storage Engine 15.3 The MEMORY Storage Engine15.4 The CSV Storage Engine 15.5 The ARCHIVE Storage Engine15.6 The BLACKHOLE Storage Engine15.7 The MERGE Storage Engine 15.8 The FEDERATED Storage Engine 15.9 The EXAMPLE Storage Engine15.10 Other Storage Engines15.11 Overview of MySQL Storage Engine Architecture

Storage engines are MySQL components that handle the SQL operations for different table types. InnoDB is the default and most general-purpose storage engine, and Oracle recommends using it for tables except for specialized use cases. (The CREATE TABLE statement in MySQL 5.7 creates InnoDB tables by default.)

MySQL Server uses a pluggable storage engine architecture that enables storage engines to be loaded into and unloaded from a running MySQL server.

To determine which storage engines your server supports, use the SHOW ENGINES statement. The value in the Support column indicates whether an engine can be used. A value of YES, NO, or DEFAULT indicates that an engine is available, not available, or available and currently set as the default storage engine.

mysql> SHOW ENGINES\G
*************************** 1. row ***************************
      Engine: PERFORMANCE_SCHEMA
     Support: YES
     Comment: Performance Schema
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 2. row ***************************
      Engine: InnoDB
     Support: DEFAULT
     Comment: Supports transactions, row-level locking, and foreign keys
Transactions: YES
          XA: YES
  Savepoints: YES
*************************** 3. row ***************************
      Engine: MRG_MYISAM
     Support: YES
     Comment: Collection of identical MyISAM tables
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 4. row ***************************
      Engine: BLACKHOLE
     Support: YES
     Comment: /dev/null storage engine (anything you write to it disappears)
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 5. row ***************************
      Engine: MyISAM
     Support: YES
     Comment: MyISAM storage engine
Transactions: NO
          XA: NO
  Savepoints: NO
...

This chapter covers use cases for special-purpose MySQL storage engines. It does not cover the default InnoDB storage engine or the NDB storage engine which are covered in Chapter 14, The InnoDB Storage Engine, and Chapter 21, MySQL NDB Cluster 7.5 and NDB Cluster 7.6. For advanced users, this chapter also contains a description of the pluggable storage engine architecture (see Section 15.11, “Overview of MySQL Storage Engine Architecture”).

For information about storage engine support offered in commercial MySQL Server binaries, see MySQL Enterprise Server 5.7, on the MySQL website. The storage engines available might depend on which edition of Enterprise Server you are using.

For answers to commonly asked questions about MySQL storage engines, see Section A.2, “MySQL 5.7 FAQ: Storage Engines”.

MySQL 5.7 Supported Storage Engines

• InnoDB: The default storage engine in MySQL 5.7. InnoDB is a transaction-safe (ACID compliant) storage engine for MySQL that has commit, rollback, and crash-recovery capabilities to protect user data. InnoDB row-level locking (without escalation to coarser granularity locks) and Oracle-style consistent nonlocking reads increase multi-user concurrency and performance. InnoDB stores user data in clustered indexes to reduce I/O for common queries based on primary keys. To maintain data integrity, InnoDB also supports FOREIGN KEY referential-integrity constraints. For more information about InnoDB, see Chapter 14, The InnoDB Storage Engine.
• MyISAM: These tables have a small footprint. Table-level locking limits the performance in read/write workloads, so it is often used in read-only or read-mostly workloads in Web and data warehousing configurations.
• Memory: Stores all data in RAM, for fast access in environments that require quick lookups of non-critical data. This engine was formerly known as the HEAP engine. Its use cases are decreasing; InnoDB with its buffer pool memory area provides a general-purpose and durable way to keep most or all data in memory, and NDBCLUSTERprovides fast key-value lookups for huge distributed data sets.
• CSV: Its tables are really text files with comma-separated values. CSV tables let you import or dump data in CSV format, to exchange data with scripts and applications that read and write that same format. Because CSV tables are not indexed, you typically keep the data in InnoDB tables during normal operation, and only use CSV tables during the import or export stage.
• Archive: These compact, unindexed tables are intended for storing and retrieving large amounts of seldom-referenced historical, archived, or security audit information.
• Blackhole: The Blackhole storage engine accepts but does not store data, similar to the Unix /dev/null device. Queries always return an empty set. These tables can be used in replication configurations where DML statements are sent to slave servers, but the master server does not keep its own copy of the data.
• NDB (also known as NDBCLUSTER): This clustered database engine is particularly suited for applications that require the highest possible degree of uptime and availability.
• Merge: Enables a MySQL DBA or developer to logically group a series of identical MyISAM tables and reference them as one object. Good for VLDB environments such as data warehousing.
• Federated: Offers the ability to link separate MySQL servers to create one logical database from many physical servers. Very good for distributed or data mart environments.
• Example: This engine serves as an example in the MySQL source code that illustrates how to begin writing new storage engines. It is primarily of interest to developers. The storage engine is a “stub” that does nothing. You can create tables with this engine, but no data can be stored in them or retrieved from them.

You are not restricted to using the same storage engine for an entire server or schema. You can specify the storage engine for any table. For example, an application might use mostly InnoDB tables, with one CSV table for exporting data to a spreadsheet and a few MEMORY tables for temporary workspaces.

Choosing a Storage Engine

The various storage engines provided with MySQL are designed with different use cases in mind. The following table provides an overview of some storage engines provided with MySQL, with clarifying notes following the table.

Table 15.1 Storage Engines Feature Summary

Notes:

1. Implemented in the server, rather than in the storage engine.

2. Compressed MyISAM tables are supported only when using the compressed row format. Tables using the compressed row format with MyISAM are read only.

3. Implemented in the server via encryption functions. Data-at-rest tablespace encryption is available in MySQL 5.7 and later.

4. Support for foreign keys is available in MySQL Cluster NDB 7.3 and later.

5. InnoDB support for FULLTEXT indexes is available in MySQL 5.6 and later.

6. InnoDB support for geospatial indexing is available in MySQL 5.7 and later.

7. InnoDB utilizes hash indexes internally for its Adaptive Hash Index feature.

8. See the discussion later in this section.