dbc_min_pct
dbc_min_pct defines the minimum percentage of memory to be
used by dynamic buffer cache.
2
90
5
Specify integer value. For more information, see Specifying Parameter Values.
During file-system I/O operations, data is stored in a buffer cache, the
size of which can be fixed or dynamically allocated. When the
parameters bufpages
and nbuf are both set to
their default value of 0, the size of the buffer cache grows or shrinks
dynamically, depending on competing requests for system memory.
The value of dbc_min_pct specifies the minimum percentage
of physical memory that is reserved for use by the dynamic buffer
cache.
It is possible to set both dbc_min_pct and dbc_max_pct to the same
value, 12 for example, and create a kernel that uses
exactly that percentage of physical memory for the buffer cache,
regardless of the size of physical memory.
If dbc_min_pct is set to too low a value, very high demand
on the buffer cache can effectively hang the system. The is also true
when using fixed buffer cache. To determine a reasonable (and
conservative) value for the minimum cache size in Mbytes, use the
following formula:
(number of system processes) * (largest
file-system block size) / 1024
To determine the value for dbc_min_pct, divide the result by the
number of Mbytes of physical memory installed in the computer and
multiply that value by 100 to obtain the correct value in percent.
Only those processes that actively use disk I/O should be included in the calculation. All others can be excluded. Here are some examples of what processes should be included in or excluded from the calculation:
nroff, database management applications,
text editors, compilers, etc. that access or use source
and/or output files stored in one or more file systems
mounted on the system.
hpterm,
rlogin, login shells, system daemons,
telnet or uucp connections,
etc. These process use very little, if any, disk
I/O.
dbc_min_pct must be less than or equal to dbc_max_pct .
To use dynamic buffer caching,
bufpages and
nbuf must both be set to zero.