MonetDB用户指南4——(资源)磁盘空间

原文：http://www.monetdb.org/Documentation/Userguide/diskspace

Disk space

        

The disk space footprint is determined by the way columns are being stored. MonetDB uses dictionary encoding for string columns, but aside from this there is no default compression applied to reduce the disk footprint. The prime reason being the two-headed sword of compression. It safes (cheap) disk space and IO bandwidth at the cost of expensive CPU (de)compression overhead (Seecompression). Since all columns are memory mapped upon access, i.e. they need not be decompressed.  If disk space comes at a premium and memory residency can be guaranteed for a long time, then one of the compression optimizers may become helpful.

The disk footprint can be assessed using the (Linux) command 'du' on the dbfarm directory or to run the query 'select * from storage();', provided the sql extensions are pre-loaded into your database. (Seestorage model)

磁盘空间是由列的方式被存储。MonetDB使用字典编码为字符串列，但除了这个，没有默认压缩以减少硬盘占用量。首要原因是压缩的两面性。（便宜）磁盘空间和IO带宽和成本昂贵的CPU（DE）的压缩开销（见压缩）。由于所有列是内存映射访问时，即他们需要无法解压缩。如果磁盘空间来可以保证和内存驻留很长一段时间，压缩优化可能很有帮助。

磁盘占用，可以使用（Linux）命令“du”评估，在dbfarm目录或运行查询“SELECT * FROM storage（);'可以评估，需要预先加载到你的数据库SQL扩展。（见存储模型）