注意：
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sqlite3只支持一写多读. 读与读可以同时进行 读与写不可同时进行 写与写不可同时进行 |
什么时候会返回SQLITE_BUSY错误码？
官方文档给出的解释是：
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The SQLITE_BUSY result code indicates that the database file could not be written (or in some cases read) because of concurrent activity by some other database connection, usually a database connection in a separate process. For example, if process A is in the middle of a large write transaction and at the same time process B attempts to start a new write transaction, process B will get back an SQLITE_BUSY result because SQLite only supports one writer at a time. Process B will need to wait for process A to finish its transaction before starting a new transaction. The sqlite3_busy_timeout() and sqlite3_busy_handler() interfaces and the busy_timeout pragma are available to process B to help it deal with SQLITE_BUSY errors. |
SQLite只支持库级锁，库级锁意味着什么？——意味着同时只能允许一个写操作，也就是说，即事务T1在A表插入一条数据，事务T2在B表中插入一条数据，这两个操作不能同时进行，即使你的机器有100个CPU，也无法同时进行，而只能顺序进行。表级都不能并行，更别说元组级了——这就是库级锁。但是，SQLite尽量延迟申请X锁，直到数据块真正写盘时才申请X锁，这是非常巧妙而有效的。
简单的办法，全局加锁，单线程执行，复杂一点，则可以启用一个专门的数据库线程异步执行操作。
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Many concurrent writers? → choose client/server If many threads and/or processes need to write the database at the same instant (and they cannot queue up and take turns) then it is best to select a database engine that supports that capability, which always means a client/server database engine. SQLite only supports one writer at a time per database file. But in most cases, a write transaction only takes milliseconds and so multiple writers can simply take turns. SQLite will handle more write concurrency than many people suspect. Nevertheless, client/server database systems, because they have a long-running server process at hand to coordinate access, can usually handle far more write concurrency than SQLite ever will. |
参考链接
- sqlite3 database is locked解决方案
- SQLiteException: database is locked异常的解决
- 解决SQLite database is locked
- SQLITE_BUSY
- SQLite Begin Concurrent
- What does, if many threads and/or processes need to write the database at the same instant, mean?
- Appropriate Uses For SQLite
- SQLiteDatabaseLockedException: database is locked
- Why are concurrent writes not allowed on an SQLite database?