Re: Oracle on AIX hangs

That link certainly is a good resource. Just a caution to casual readers, though, the the particular settings described in that article don't necessarily describe what you would really want on an Oracle database server. (On my servers, where I still use JFS, I usually set minperm/maxperm to something in the range of 5/10 to 10/20.)

Anyway, there are definitely useful tips for JFS2 users. An important JFS2 tip that *is* relevant to Oracle servers is "concurrent I/O" (CIO). JFS2 users who use concurrent I/O may find that their settings of minperm/maxperm/maxclient/whatever are almost irrelevant (okay, /those/ are brave words!) because database I/O will bypass filesystem buffers entirely...

On AIX with JFS2, CIO is definitely your friend. Or, at least, that's been my experience...


Adrian wrote:

Brandon,

As previously discussed, I also have these issues periodically.

Found this from aixtips.com which looks possibly relevant. Basically Maxperm
does not restrict memory usage alone.

http://www.circle4.com/jaqui/eserver/aixtra-May05-TuningJFS2.pdf

Like most UNIX systems, AIX leaves in memory the pages-from local JFS, JFS2
or remote (NFS) file systems-of files that have been read or written. If
they're referenced again, it saves an I/O operation, as they're already in
memory. Since reads usually involve just a pagein-whereas computational- or
workingset pages tend to involve both a pagein and a pageout-it's useful to
tweak the minperm and maxperm values to favor computational pages. However,
maxperm only affects JFS. JFS2's correct parameter is maxclient and many I/O
problems that I look at involve misunderstandings about this parameter.
For JFS, maxperm specifies the file-page value (%) above which the page
stealer should steal only file pages. The default is 80 percent, but this
isn't a hard limit. If you set maxperm to 30 percent and the pages
are available, I/O can still use up to 100 percent of memory. What you're
changing is which pages get stolen when a page is needed. On the other end
of the scale, minperm specifies the file-page value (%) below which the page
stealer steals both file and computational pages. When the percentage of
file pages falls between minperm and maxperm, the page stealer steals file
pages unless the number of file repages exceeds the number of computational
repages.

Not at work, so cant check my settings, but looks like the maxperm may not
restrict memory as expected without tweaking strict_maxclient.

HTH

Adrian



-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Allen, Brandon
Sent: 26 January 2006 22:33
To: Paul G Parker; oracle-l@xxxxxxxxxxxxx; MARK BRINSMEAD
Subject: RE: Oracle on AIX hangs

Yes, minperm and maxperm have been restricted:

/usr/sbin ->vmstat -v|grep perm
     10.0 minperm percentage
     20.0 maxperm percentage

hdisk0 contains the swap space and it appears we were paging/swapping to
death:

/usr/sbin ->lsps -a
Page Space      Physical Volume   Volume Group    Size %Used Active  Auto
Type
hd6             hdisk0            rootvg       10240MB     1     yes   yes
l

/opt/oracle ->vmstat 15
System Configuration: lcpu=4 mem=15808MB
kthr       memory              page              faults           cpu
-----   -----------   ------------------------  ------------    -----------
r  b   avm      fre  re  pi   po   fr    sr cy in   sy    cs    us sy id wa
2  7   4965756   27   0   2    2  437   514  0 1388 30629 13078 11  5 73 11
1  180 4985880  503   0  56 1278 1411  1971  0 1311  5568  2984 27  4  0 69
2  184 4998310    0   0  36  741  853 10011  0 1250  6287  1733 28  3  0 69
1  184 5015464    0   0  44 1069 1228 10090  0 1283  4044  2431 28  3  0 69
1  190 5019796  527   0  43  349  341   382  0 1216  3377  1323 27  1  0 71
1  200 5031743  277   0  41  743  819   951  0 1225  2585  1924 27  2  0 71


Now to figure out why . . .

Thanks,
Brandon


-----Original Message----- From: parkerpg@xxxxxxxxx [mailto:parkerpg@xxxxxxxxx]On Behalf Of Paul G Parker Sent: Thursday, January 26, 2006 3:19 PM To: Allen, Brandon; oracle-l@xxxxxxxxxxxxx Subject: Re: Oracle on AIX hangs


Brandon,
The default settings on AIX for Virtual Memory Management are inappropriate
for a database server. Confirm the settings of minperm and maxperm (use vmstat -v) and check out
Metalink note: 316533.1


Another useful site reference is www.aixtips.com

Paul



On 1/26/06, Allen, Brandon <Brandon.Allen@xxxxxxxxxxx> wrote:
Yes, I think you might be right - see attached.  Unfortunately I didn't save
the output of lsps, but I did run it and I'm pretty sure it said 49% used.
Now we just need to find the cause of the paging.

Thanks,
Brandon


-----Original Message----- From: parkerpg@xxxxxxxxx [mailto:parkerpg@xxxxxxxxx]On Behalf Of Paul G Parker Sent: Thursday, January 26, 2006 2:29 PM To: Allen, Brandon Subject: Re: Oracle on AIX hangs


Brandon,

My guess would be excessive paging.  What is the output of lsps -a ?
Do you have any vmstat output during this "hang"?

Paul



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