Database System Implementation

Chapter13 第二级存储管理

 

Especially import for understanding the operation of  a database system is the fact that the disk is organized into disk blocks of perhaps 4-64 KB.Entire blocks are moved to  or from  a  continuous section of main memory called a buffer .Thus , a key technique for speeding up database operations is to arrange data so that when one piece of  a disk block is needed,it is likely that other data on the same block will also be needed at about the same time.

 

A significant part of the complexity in a DBMS comes from the requirement that no change to the database can be considered final until it has migrated tononvolatile, secondary storage.

 

Virtual memory is an artifact of the operating system andits use of the machine's hardware, and it is not a level of the memory hierarchy.

 

Main-memory database systems, like most applications , are most useful when the data is small enough to remain in main memory without being swapped out by the operating system.

 

13.2