dbc_max_pct and db_buffer_cache difference

[???_185]

I know dbc_max_pct usage is used to increase when use of process is much.
dbc_max_pct and dbc_min_pct are the area in system. db don't use this field.
db contains SGA itself.
so, I want to know what kind of system process is using this area.
and,mainly what kind of process use system buffer cache area?

Thanks Regard.

[Arunvijai_4]

This doc has got good information about dbc_max_pct and other mass storage parameters.

http://docs.hp.com/en/939/KCParms/KCparam.DBCmaxPct.html

-Arun

[Zeev Schultz]

Any kind that works with file systems as the name itself says: "file system buffer cache space".It buffers the file system I/O between application and disk resources.So if your app uses less filesystems I/O (like raw devices) it becomes less important.


http://docs.hp.com/en/939/KCParms/KCparam.DBCmaxPct.html

[saju_2]

Hi

This is one of the most discussed parmater related to oracle in itrc.

The buffer cache is an area of memory where pages from the secondary storage devices are
stored. The buffer cache is used to reduce access to the secondary storage devices by storing frequently accessed pages in memory.
Once the file data is in memory, subsequent access can be performed in memory, without the need to access the secondary storage device.


There is static and dynamic buffer cache. If in ur server the nbuf and bufpages parameters are set to zero, then dynamic buffer cahe is used.

When the system is initially booted, the system allocates dbc_min_pct (default 5%) of memory for buffer pages (each page is 4096 bytes). The system also allocates 1 buffer header for every 2 buffer pages. The size of the buffer cache will grow as new pages are brought in from disk. The buffer cache can expand very rapidly, so that it uses the maximum percentage of memory specified by dbc_max_pct. A large file copy and backups are operations that can cause the buffer cache to quickly reach its maximum size. While the buffer cache expands quickly, it decreases in size only when there is memory pressure.

U can get more information about buffer cache and dbc max pct from the attached document.

regards
CS

[saju_2]

Hi

Sorry i missed the attachment. In this doc there is one chapter on buffer cache.


Regards
CS

[Zeev Schultz]

Particulary for Oracle,this discussion on their 's forum may be interesting:

http://asktom.oracle.com/pls/ask/f?p=4950:8:::::F4950_P8_DISPLAYID:7931107631402