最近几年来，地理信息系统无论是在理论上还是应用上都处在一个飞速发展的阶段。 GIS被应用于多个领域的建模和决策支持，如城市管理、区划、环境整治等等，地理信息成为信息时代重要的组成部分之一； “数字地球”概念的提出，更进一步推动了作为其技术支撑的GIS的发展。 与此同时，一些学者致力于相关的理论研究，如空间感知、空间数据误差、空间关系的形式化等等。 这恰好说明了地理信息系统作为应用技术和学科的两个方面，并且这两个方面构成了相互促进的发展过程。
VACUUM The command copies the contents of the master database to a tempdb file, then empties the master database, and reloads the original database file from the replica. This eliminates free pages, arranges the data in the table as contiguous, and cleans up the database file structure.
If there is no explicit integer primary key (INTEGER PRIMARY KEY) in the table, the VACUUM command may change the row ID (ROWID) of the items in the table. The VACUUM command is only applicable to the primary database, and additional database files are impossible to use. VACUUM Orders.
If there is an active transaction, the The following is issued to the entire database at the command prompt You can also visit the You can also run it on a specific table SQLite’s In the SQLite prompt, you can enable / disable it through the following compilation You can run the following command from a command prompt to check VACUUM command fails. The VACUUM command is any operation for an in-memory database. Due to VACUUM Command to recreate the database file from scratch, so VACUUM It can also be used to modify many database-specific configuration parameters. 1.44.1. Manual VACUUM ¶
VACUUM Syntax for the command:$sqlite3 database_name "VACUUM;"
SQLite Run at the prompt VACUUM , as follows:sqlite> VACUUM;
VACUUM , as follows:sqlite> VACUUM table_name;
1.44.2. Automatic VACUUM (Auto-VACUUM) ¶
Auto-VACUUM Vs. VACUUM Different, it just moves free pages to the end of the database, thereby reducing the size of the database. By doing so, it can obviously fragment the database, while VACUUM Is anti-fragmentation. So Auto-VACUUM It only makes the database smaller. SQLite Of Auto-VACUUM :sqlite> PRAGMA auto_vacuum = NONE; -- 0 means disable auto vacuum sqlite> PRAGMA auto_vacuum = INCREMENTAL; -- 1 means enable incremental vacuum sqlite> PRAGMA auto_vacuum = FULL; -- 2 means enable full auto vacuum
auto-vacuum Set up:$sqlite3 database_name "PRAGMA auto_vacuum;"