Sqlite事务模型、性能优化Tips、常见误区

This option sets the threading mode to Multi-thread. In other words, it disables mutexing on database connection and prepared statement objects. The application is responsible for serializing access to database connections and prepared statements. But other mutexes are enabled so that SQLite will be safe to use in a multi-threaded environment as long as no two threads attempt to use the same database connection at the same time.

SQLITE_CONFIG_SERIALIZED(串行模式)

This option sets the threading mode to Serialized. In other words, this option enables all mutexes including the recursive mutexes on database connection and prepared statement objects. In this mode (which is the default when SQLite is compiled with SQLITE_THREADSAFE=1) the SQLite library will itself serialize access to database connections and prepared statements so that the application is free to use the same database connection or the same prepared statement in different threads at the same time.

4.1.1 误区一：多线程模式是线程安全的

产生这个误区主的主要原因是官方文档里的最后一句话：

SQLite will be safe to use in a multi-threaded environment as long as no two threads attempt to use the same database connection at the same time.

但大家往往忽略了前面的一句话：

it disables mutexing on database connection and prepared statement objects

即对于单个连接的读、写操作，包括创建出来的prepared statement操作，都没有线程安全的保护。也即在多线程模式下，对单个连接的操作，仍需要在业务层进行锁保护。

4.1.2 误区二：多线程模式下，并发读操作是安全的

关于这一点，#2.4给出了具体的解释;多线程模式下(SQLITE_CONFIG_MULTITHREAD)对prepared statement、connection的操作都不是线程安全的

4.1.3 误区三：串行模式下，所有数据库操作都是串行执行

这个问题比较笼统;即使在串行模式下，所有的数据库操作仍需遵循事务模型;而事务模型已经将数据库操作的锁进行了非常细粒度的分离，串行模式的锁也是在上层保证了事务模型的完整性

4.1.4 误区四：多线程模式性能最好，串行模式性能差

多线程模式下，仍需要业务上层进行锁保护，串行模式则是在sqlite内部进行了锁保护;认为多线程模式性能好的兄弟哪来的自信认为业务层的锁实现比sqlite内部锁实现性能更高?

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