SQLite.NET提供程式的選擇

今日用到了SQLite，發現這個資料庫進行了很大的升級，從3.4.X升級到3.5.X了。版本號發生改變，API介面OS層發生重大改變。

SQLite version 3.5.0 introduces a new OS interface layer that is incompatible with all prior versions of SQLite. In addition, a few existing interfaces have been generalized to work across all database connections within a process rather than just all connections within a thread. The purpose of this article is to describe the changes to 3.5.0 in detail so that users of prior versions of SQLite can judge what, if any, effort will be required to upgrade to newer versions.

1.0 Overview Of Changes

A quick enumeration of the changes in SQLite version 3.5.0 is provide here. Subsequent sections will describe these changes in more detail.

1. The OS interface layer has been completely reworked:
   1. The undocumented sqlite3_os_switch() interface has been removed.
   2. The SQLITE_ENABLE_REDEF_IO compile-time flag no longer functions. I/O procedures are now always redefinable.
   3. Three new objects are defined for specifying I/O procedures: sqlite3_vfs, sqlite3_file, and sqlite3_io_methods.
   4. Three new interfaces are used to create alternative OS interfaces: sqlite3_vfs_register(), sqlite3_vfs_unregister(), and sqlite3_vfs_find().
   5. A new interface has been added to provided additional control over the creation of new database connections: sqlite3_open_v2(). The legacy interfaces of sqlite3_open() and sqlite3_open16() continue to be fully supported.
2. The optional shared cache and memory management features that were introduced in version 3.3.0 can now be used across multiple threads within the same process. Formerly, these extensions only applied to database connections operating within a single thread.
   1. The sqlite3_enable_shared_cache() interface now applies to all threads within a process, not to just the one thread in which it was run.
   2. The sqlite3_soft_heap_limit() interface now applies to all threads within a process, not to just the one thread in which it was run.
   3. The sqlite3_release_memory() interface will now attempt to reduce the memory usages across all database connections in all threads, not just connections in the thread where the interface is called.
   4. The sqlite3_thread_cleanup() interface has become a no-op.
3. Restrictions on the use of the same database connection by multiple threads have been dropped. It is now safe for multiple threads to use the same database connection at the same time.
4. There is now a compile-time option that allows an application to define alternative malloc()/free() implementations without having to modify any core SQLite code.
5. There is now a compile-time option that allows an application to define alternative mutex implementations without having to modify any core SQLite code.

Of these changes, only 1a and 2a through 2c are incompatibilities in any formal sense. But users who have previously made custom modifications to the SQLite source (for example to add a custom OS layer for embedded hardware) might find that these changes have a larger impact. On the other hand, an important goal of these changes is to make it much easier to customize SQLite for use on different operating systems.

由於儲存層的改變，SQLite.NET的各個版本也發生了變化：

SQLite.NET 1.0.46是最後一個基於3.4.X版本的提供程式；
SQLite.NET 1.0.48是當前最新的基於3.5.4程式碼的提供程式；

SQLite.NET的新版本主要是隨SQLite3.4->3.5的改進而進行了相應的修改。效能有很大變化，對比如下：

由測試可知，3.4版的SQLite在很多方面，效能依然要比3.5版的SQLite強不少。但是SQLite 3.5版在OS適配層的改進（引入VFS物件），提高了資料的寫入效率，明顯的，其Commits的時間總是較少。

結論：
3.4版的SQLite在資料插入較多的應用情況下，效率仍然較好；
3.5版的SQLite在資料寫入磁碟方面有很大改進，但其顯然在記憶體資料組織方面還有待改進，插入操作所耗費的時間明顯比3.4版要長；

感覺3.4版的SQLite是非常穩定的一個版本。3.5版，看來等等再使用了。

本文轉自斯克迪亞部落格園部落格，原文連結：http://www.cnblogs.com/sgsoft/archive/2008/02/19/1074055.html，如需轉載請自行聯絡原作者