topic Re: %wcache in Operating System - HP-UX

%wcache

Steve_3 — Thu, 29 Nov 2001 20:56:48 GMT

Why is my %wcache so low?

%wcache should be > 95%

bufpages=0
dbc_max_pct=2
dbc_min_pct=2
nbuf=0

3 Gig memory

14:44:30 bread/s lread/s %rcache bwrit/s lwrit/s %wcache pread/s pwrit/s
14:44:35 0 165 100 7 9 25 0 0
14:44:40 0 164 100 10 11 16 0 0
14:44:45 3 47 94 20 28 28 0 0
14:44:50 1 5 87 7 7 6 0 0
14:44:55 0 2 100 5 4 0 0 0
14:45:00 8 79 90 24 25 6 0 0
14:45:05 0 233 100 12 19 38 0 0
14:45:10 1 234 100 6 8 22 0 0
14:45:15 2 146 99 21 24 12 0 0
14:45:20 0 8 95 11 12 5 0 0
14:45:25 0 8 100 8 7 0 0 0
14:45:30 0 5 96 8 9 9 0 0
14:45:35 5 43 89 28 33 17 0 0
14:45:40 0 151 100 7 7 5 0 0
14:45:45 2 161 99 23 13 0 0 0

thanks,
steve

Re: %wcache

Sridhar Bhaskarla — Thu, 29 Nov 2001 21:04:11 GMT

Steve,

2% of 3 Gig is 60MB. I guess you may be short of your cache size.

However, it is really dependent on the type of application. If it does a lot of synchronous I/O, then there will not be much help from cache. If it does asynchronous I/O, then you can see dramatic improvement if you increase the buffer cache.

Also setting buffer cache too high will hamper the memory for the applications. Around 300 MB should be fine.

Also, check your sar -u values. If you %wio above 20% and if your %wcache is constantly below 60, then you may gain by increasing the dbc_max_pct provided your application does asynchronous writes.

You may need to try with different sizes and see what fits the best.

-Sri

Re: %wcache

Sanjay_6 — Thu, 29 Nov 2001 21:14:22 GMT

Hi Steve,

Take a look at the thread below,

http://us-support2.external.hp.com/cki/bin/doc.pl/sid=3cffc6d515076c2303/screen=ckiSearchResults?mode=id&searchString=A4460661

http://docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/B2355-90742/B2355-90742_top.html&con=/hpux/onlinedocs/B2355-90742/00/00/57-con.html&toc=/hpux/onlinedocs/B2355-90742/00/00/57-toc.html&searchterms=system%20performance&queryid=20011129-131626

Hope this helps.

Regds

Re: %wcache

Marco Paganini — Fri, 30 Nov 2001 05:23:06 GMT

Hello Steve,

You should (IMHO) increase your dbc_max_pct. However, depending on the writing patterns of your application you may get little benefit out of it (say, if you have a lot of sequential I/O and few rewrites). Also, if you have a database using raw devices, that setting may be of little use (since the RDBMS system uses its own buffering mechanisms).

Regards,
Paga