計算機外文翻譯--數據庫結構

1、- 1 -外文原文Database ConfigurationSQLite doesn’t have a configuration file. Rather, all of its configuration parameters are implemented using pragmas. Pragmas work in different ways. Some are like variables; others are like

2、 commands. They cover many aspects of the database, such as runtime information, database schema, versioning, file format, memory use, and debugging. Some pragmas are read and set like variables, while others require arg

3、uments and are called like functions. Many pragmas have both temporary and permanent forms. Temporary forms affect only the current session for the duration of its lifetime. The permanent forms are stored in the database

4、 and affect every session. The cache size is one such example.This section covers the most commonly used pragmas. A complete list of all SQLite pragmas can be found in Appendix A.The Connection Cache SizeThe cache size p

5、ragmas control how many database pages a session can hold in memory.To set the default cache size for the current session, you use the cache_size pragma:sqlite> PRAGMA cache_size;cache_size---------------2000sqlite>

6、; PRAGMA cache_size=10000;sqlite> PRAGMA cache_size;cache_size---------------10000You can permanently set the cache size for all sessions using the default_cache_sizepragma. This setting is stored in the database. Thi

7、s will only take effect for sessions created after the change, not for currently active sessions.- 3 -0 main /tmp/foods.db2 db2 /tmp/dbsqlite> CREATE INDEX foods_name_type_idx ON foods(name,type_id);sqlite> PRAGMA

8、index_info(foods_name_type_idx);seqn cid name---- ------- --------------------0 2 name1 1 type_idsqlite> PRAGMA index_list(foods);seq name unique----- ------------------- ---------------0 foods_name_type_idx 0sqlite&g

9、t; PRAGMA table_info(foods);cid name type notn dflt pk----- --------------- --------------- ---- ---- ----------0 id integer 0 11 type_id integer 0 02 name text 0 0Synchronous WritesNormally, SQLite commits all changes t

10、o disk at critical moments to ensure transaction durability.However, it is possible to turn this off for performance gains. You do this with the synchronous pragma. There are three settings: FULL, NORMAL, and OFF. They a

11、re defined as follows:? FULL: SQLite will pause at critical moments to make sure that data has actually been written to the disk surface before continuing. This ensures that if the operating system crashes or if there is