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                # 存儲引擎 ## 1. 存儲引擎概述 **存儲引擎類似于底層軟件組織**,數據庫管理系統(DBMS)使用數據引擎進行創建、查詢、更新和刪除數據。不同的存儲引擎提供不同的**存儲機制、索引技巧、鎖定水平**等功能,使用不同的存儲引擎,還可以獲得特定的功能。現在許多不同的數據庫管理系統都支持多種不同的數據引擎。 和大多數的數據庫不同, MySQL中有一個存儲引擎的概念, 針對不同的存儲需求可以選擇最優的存儲引擎。 ? 存儲引擎就是存儲數據,建立索引,更新查詢數據等等技術的實現方式 。存儲引擎是基于表的,而不是基于庫的。所以存儲引擎也可被稱為表類型。 ? Oracle,SqlServer等數據庫只有一種存儲引擎。MySQL提供了插件式的存儲引擎架構。所以MySQL存在多種存儲引擎,可以根據需要使用相應引擎,或者編寫存儲引擎。 ? MySQL5.0支持的存儲引擎包含 : InnoDB 、MyISAM 、BDB、MEMORY、MERGE、EXAMPLE、NDB Cluster、ARCHIVE、CSV、BLACKHOLE、FEDERATED等,其中InnoDB和BDB提供事務安全表,其他存儲引擎是非事務安全表。 可以通過指定 show engines , 來查詢當前數據庫支持的存儲引擎 : ~~~ mysql> show engines\G; *************************** 1. row *************************** Engine: ARCHIVE Support: YES Comment: Archive storage engine Transactions: NO XA: NO Savepoints: NO *************************** 2. row *************************** Engine: BLACKHOLE Support: YES Comment: /dev/null storage engine (anything you write to it disappears) Transactions: NO XA: NO Savepoints: NO *************************** 3. row *************************** Engine: MRG_MYISAM Support: YES Comment: Collection of identical MyISAM tables Transactions: NO XA: NO Savepoints: NO *************************** 4. row *************************** Engine: FEDERATED Support: NO Comment: Federated MySQL storage engine Transactions: NULL XA: NULL Savepoints: NULL *************************** 5. row *************************** Engine: MyISAM Support: YES Comment: MyISAM storage engine Transactions: NO XA: NO Savepoints: NO *************************** 6. row *************************** Engine: PERFORMANCE_SCHEMA Support: YES Comment: Performance Schema Transactions: NO XA: NO Savepoints: NO *************************** 7. row *************************** Engine: InnoDB Support: DEFAULT Comment: Supports transactions, row-level locking, and foreign keys Transactions: YES XA: YES Savepoints: YES *************************** 8. row *************************** Engine: MEMORY Support: YES Comment: Hash based, stored in memory, useful for temporary tables Transactions: NO XA: NO Savepoints: NO *************************** 9. row *************************** Engine: CSV Support: YES Comment: CSV storage engine Transactions: NO XA: NO Savepoints: NO 9 rows in set (0.00 sec) ~~~ 創建新表時如果不指定存儲引擎,那么系統就會使用默認的存儲引擎,MySQL5.5之前的默認存儲引擎是MyISAM,5.5之后就改為了InnoDB。 查看Mysql數據庫默認的存儲引擎 , 指令 : ``` show variables like '%storage_engine%' ; ``` ~~~ mysql> show variables like '%storage_engine%'; +----------------------------------+-----------+ | Variable_name | Value | +----------------------------------+-----------+ | default_storage_engine | InnoDB | | default_tmp_storage_engine | InnoDB | | disabled_storage_engines | | | internal_tmp_disk_storage_engine | InnoDB | | internal_tmp_mem_storage_engine | TempTable | +----------------------------------+-----------+ 5 rows in set (0.00 sec) ~~~
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