Globally buffering files uses system resources. To find out how much address space and memory globally buffering a data file will require, enter the following at the DCL prompt:
$DIRECTORY/FULL myfile.dat
MYFILE.DAT;1 File ID: (1316,116,0)
.
.
.
File attributes: Allocation: 13314, Extend: 90,
Maximum bucket size: 6
Global buffer count: 50, Version limit: 3
.
.
.
Total of 1 file, 13314/13314 blocks.
One of the file attributes displayed is the maximum bucket size. The
Global buffer count will also be displayed if global buffering has
been set on this file.
A.1.1 Address Space
ADDRESS SPACE = Maximum bucket size x Global buffer count
The amount of address space consumed EACH time the file is opened is Maximum bucket size times Global buffer count. For example, from doing Directory/full on myfile.dat we see:
Maximum bucket size = 6
Global buffer count = 20
----
120 address pages will be used EACH
time the file is opened.
PHYSICAL MEMORY = Zero to Maximum bucket size x
Global buffer count
The amount of physical memory consumed NO MATTER HOW MANY TIMES the file is open is zero to Maximum bucket size times Global buffer count. For example, from doing Directory/full on myfile.dat we see:
Maximum bucket size = 6
Global buffer count = 20
----
0 to 120 pages of physical memory
NO MATTER HOW MANY TIMES
the file is open.
Use these calculations to determine the number of global buffers to add to your hot files.