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System Architecture 2-47
Shared-Memory Header
OnLine compares the item key with the key value it is searching for. If the
values match, the item is located. If not, each item in the linked list is
examined in succession until the item is found or the search is ended.
Figure 2-6 illustrates a hashing technique that uses an algorithm that looks at
the first letter of the key value.
Shared-Memory Header
The shared-memory header contains a description of the size of all other
structures in OnLine shared memory, including internal tables and the
OnLine buffer pool. (The tbstat display header contains the size of shared
memory, expressed in kilobytes.)
The shared-memory header also contains pointers to the location of these
structures. When a user process first attaches to shared memory, it reads
address information in the shared-memory header for directions to all other
structures.
The size of the shared-memory header is about one kilobyte, although the
size varies, depending on the machine platform. The administrator cannot
tune the size of the header.
Figure 2-6
This simple
example of a
hashing technique
uses an algorithm
that looks at the
first letter of the key
value.
F - L
A - E
M - Q
R - T
U - Z
Nguyen
Nguyen
Hash value
Key value
Hash algorithm
Hash-table entries Linked list of entries
with same hash value