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12-29-2009 07:46 PM
12-29-2009 07:46 PM
OS Buffer Cache
How do I find out the OS buffer Cache?
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12-29-2009 08:39 PM
12-29-2009 08:39 PM
Re: OS Buffer Cache
You can use glance utility.
Regards
Sunny
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12-29-2009 09:10 PM
12-29-2009 09:10 PM
Re: OS Buffer Cache
You can also use:
# sar -b 2 5
Report buffer activity:
bread/s
Number of physical reads per second from the disk (or other block devices) to the buffer cache;
bwrit/s
Number of physical writes per second from the buffer cache to the disk (or other block device);
lread/s
Number of reads per second from buffer cache;
lwrit/s
Number of writes per second to buffer cache;
%rcache
Buffer cache hit ratio for read requests e.g., 1 - bread/lread;
%wcache
Buffer cache hit ratio for write requests e.g., 1 - bwrit/lwrit;
pread/s
Number of reads per second from character device using the physio() (raw I/O) mechanism;
pwrit/s
Number of writes per second to character device using the physio() (that is, raw I/O) mechanism; mechanism.
See man page for more info:
http://docs.hp.com/en/B3921-60631/sar.1M.html
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12-29-2009 09:28 PM
12-29-2009 09:28 PM
Re: OS Buffer Cache
After the 11.00 release there the Buffer cache is dynamic. This is defined by the kernal parameters ( example taken from 11.23).
# kctune |grep db
dbc_max_pct 50 Default Immed
dbc_min_pct 5 Default Immed
Minimum is 5% of your total memory and maximum is 50%. If you want to make it static, configure both parameter with same value.
Buffer cache usage can be monitored using the sar command
# sar -b 1 15
HP-UX rx260-17 B.11.23 U ia64 12/30/09
00:24:50 bread/s lread/s %rcache bwrit/s lwrit/s %wcache pread/s pwrit/s
00:24:51 0 49 100 1 1 0 0 0
00:24:52 0 1 100 3 1 0 0 0
00:24:53 0 930 100 1 79 99 0 0
00:24:54 0 1 100 1 1 0 0 0
00:24:55 0 1 100 2 1 0 0 0
00:24:56 0 2 100 5 2 0 0 0
00:24:57 0 5 100 1 5 80 0 0
00:24:58 0 19 100 3 9 67 0 0
00:24:59 0 3 100 3 3 0 0 0
00:25:00 0 13 100 2 3 33 0 0
00:25:01 0 87 100 18 19 5 0 0
00:25:02 0 278 100 2 343 99 0 0
00:25:03 0 16 100 1 32 97 0 0
00:25:04 0 71 100 3 7 57 0 0
00:25:05 0 5 100 0 3 100 0 0
Average 0 99 100 3 34 91 0 0
==============================================
Regards,
Sooraj
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12-29-2009 09:57 PM
12-29-2009 09:57 PM
Re: OS Buffer Cache
Remember that Glance will nt give a complete analysis.
It will tell you whats size of the memory which is used for buffer cache
Glance - memory report (m) - bottom side
Total VM : 795mb Sys Mem : 528mb User Mem: 460mb Phys Mem : 2.0gb
Active VM: 333mb Buf Cache: 280mb Free Mem: 768mb FileCache: na
Regards,
Sooraj
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12-29-2009 11:19 PM
12-29-2009 11:19 PM
Re: OS Buffer Cache
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12-30-2009 12:05 AM
12-30-2009 12:05 AM
Re: OS Buffer Cache
Now my next question is:
my Sys Mem is very high: from glance
Total VM : 6.9gb Sys Mem : 1.7gb User Mem: 3.4gb Phys Mem : 8.0gb
Active VM: 6.5gb Buf Cache: 2.6gb Free Mem: 227mb FileCache: na
MemFS Blk Cnt: na MemFS Swp Cnt: na
How can I reduce it?
As for the Buf Cache, i can reduced it by changing dbx_min_pct and dbc_max_pct
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12-30-2009 12:19 AM
12-30-2009 12:19 AM
Re: OS Buffer Cache
decrease system kernel parameter dbc_max_pct in 10 and it will consize the system memory usage.
Regards
Sunny
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12-30-2009 12:29 AM
12-30-2009 12:29 AM
Re: OS Buffer Cache
If you are thinking you system memory usage is very high, take are of that.
What is your swap usage ?
Depending on environment reducing buffercache may reduce system performace.
Regards,
Sooraj
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