[SQLite]揭秘SQLite数据库：如何掌握事务隔离级别，避免数据不一致难题

SQLite是一种轻量级的数据库，广泛用于嵌入式系统和小型应用程序。在处理并发事务时，SQLite的事务隔离级别对于确保数据一致性至关重要。本文将深入探讨SQLite的事务隔离级别，并指导您如何避免数...

SQLite是一种轻量级的数据库，广泛用于嵌入式系统和小型应用程序。在处理并发事务时，SQLite的事务隔离级别对于确保数据一致性至关重要。本文将深入探讨SQLite的事务隔离级别，并指导您如何避免数据不一致的难题。

1. 事务与隔离级别概述

1.1 事务

事务是一组操作，这些操作要么全部成功，要么全部失败。SQLite通过确保事务的ACID属性（原子性、一致性、隔离性和持久性）来维护数据库的完整性。

1.2 隔离级别

隔离级别定义了事务之间的可见性和相互影响。SQLite提供了以下四种隔离级别：

• 读未提交（READ UNCOMMITTED）
• 读已提交（READ COMMITTED）
• 可重复读（REPEATABLE READ）
• 串行化（SERIALIZABLE）

2. 隔离级别详解

2.1 读未提交（READ UNCOMMITTED）

在最低的隔离级别下，事务可以读取其他事务尚未提交的数据。这可能导致脏读，即读取到未提交的数据，从而影响数据一致性。

2.2 读已提交（READ COMMITTED）

该级别下，事务只能读取其他事务已经提交的数据。这避免了脏读，但可能出现不可重复读，即同一事务中多次读取同一数据可能得到不同的结果。

2.3 可重复读（REPEATABLE READ）

在可重复读级别下，事务在整个执行期间只能看到已经提交的数据。这避免了脏读和不可重复读，但可能出现幻读，即事务执行期间，由于其他事务的插入或删除操作，导致读取结果不一致。

2.4 串行化（SERIALIZABLE）

这是最高的隔离级别，通过串行化事务执行来确保数据一致性。它避免了脏读、不可重复读和幻读，但会降低并发性能。

3. 选择合适的隔离级别

选择合适的隔离级别取决于您的应用需求和性能考虑。以下是一些指导原则：

• 如果您的应用对数据一致性要求不高，可以选择读未提交或读已提交级别，以提高并发性能。
• 对于需要保持数据一致性的应用，如金融系统，建议使用可重复读或串行化级别。

4. 实践示例

以下是一个SQLite示例，演示如何设置事务隔离级别：

”`sql PRAGMA journal_mode = PERSIST; PRAGMA locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -1; PRAGMA temp_store = DEFAULT; PRAGMA synchronous = OFF; PRAGMA journal_mode = WAL; PRAGMA default_cache_size = 20000; PRAGMA default_locking_mode = EXCLUSIVE; PRAGMA foreign_keys = ON; PRAGMA synchronous = ON; PRAGMA cache_size = -