Database Reference
In-Depth Information
Address
01
02
03
04
05
06
07
08
09
10
SerialNo. Size
Color
Next Serial No.
File with linked list
34578
12
Blue
08
21933
14
Green
04
Last serial
number
51373
10
Green
05
21934
10
Yellow
10
51477
3
Blue
06
61245
5
Pink
07
First serial
number
71922
6
Blue
null
51372
7
Green
3
12122
8
Yellow
2
21945
4
Purple
1
How file with linked
list is stored
34578
08
21933
04
51373
05
21934
10
51477
06
61245
07
71922
null
51372
3
12122
2
21945
1
Figure 12-9
File with a linked list.
•
Absolute addresses are device-dependent. If you need to reorganize the file
or move the file to a different storage medium, you have to change all the
addresses in the linked list. This could be a major disadvantage.
•
On the other hand, absolute addresses provide a fast method for retrieving
records in the sequence of the linked list. You fetch each record, get the address
of the next record, and use that address directly to get the next record, and so
on.
Relative addresses.
Each record in the linked list contains a relative address, not
the actual physical address, to point to the next record. The relative address of a
storage location is a number indicating the relative offset of the location from the
beginning of the storage device.
•
Relative addresses are device-independent. If you need to reorganize the file
or move the file to a different storage medium, you do not have to change the
addresses in the linked list.
•
On the other hand, data storage and retrieval are slower with relative addresses.
Every time you want to store or retrieve a record, you have to calculate the
actual physical address from the relative address. You have to contend with
address-resolution overhead.
RAID Technology Basics
Currently, in most organizations, disk storage devices form the primary media
for databases. Because storage management is part of the physical design consid-
erations, we need to discuss the nature of disk storage devices. Although disk storage
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