Re: Solaris 10 and Oracle 10g - swap space problem

From: Tanel Poder <tanel_at_poderc.com>
Date: Sun, 2 Aug 2009 23:45:55 +0800
Message-ID: <4602f23c0908020845s58ef8479j1e7c5c1cebeefdb9_at_mail.gmail.com>

Hmm... Solaris 10 may be doing something different here. I last tested on Solaris 8 and I'm pretty sure things worked like I said with it. On the other hand, Solaris 8 was released over 10 years ago :)

Time to remember Jonathan Lewis'es article which had something like this in it: "If a claim about some software behavior doesn't have a version number with it, don't trust it" :)

I think this thing needs some testing and elaboration. I'll do some checking and will get back with details soon ;-)

--
Tanel Poder
http://blog.tanelpoder.com


On Sun, Aug 2, 2009 at 1:01 AM, Riyaj Shamsudeen <riyaj.shamsudeen_at_gmail.com


> wrote:




> Tanel

>   I must disagree with you. It looks like swap is allocated even for ISM

> pages in Solaris. Please feel free to correct me if there is any

> misunderstanding from my part.

>

> Here is a small test case:

>

> RS: Intially, 7.4G of swap used

> swap -s

> total: 7207256k bytes allocated + 233128k reserved = 7440384k used,

> 40446656k available

>

> RS: ISM in use and SGA is locked as expected.

>          Address     Kbytes        RSS       Anon     Locked Mode   Mapped

> File

> ..

> 0000000380000000    6422544    6422544          -    6422544 rwxsR    [ ism

> shmid=0x300001c ]

>

> RS: No sga_max_size set in spfile either.

>

> strings  spfilePROD.ora |grep -i sga

> *.sga_target=6272M

>

> RS: Shutting down...

> sqlplus "/ as sysdba"

>

> Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit

> Production

> With the Partitioning, Real Application Clusters, OLAP, Data Mining

> and Real Application Testing options

>

> SQL> shutdown immediate;

> Database closed.

> Database dismounted.

> ORACLE instance shut down.

> SQL>

>

> RS: Just 500M of swap used after instance shutdown..

> wsqfinc1e> swap -s

> total: 451224k bytes allocated + 63928k reserved = 515152k used, 47400568k

> available

>

> RS: Restarting instance..

> ORACLE instance started.

>

> Total System Global Area 6576668672 bytes

> Fixed Size                  2050464 bytes

> Variable Size            2583696992 bytes

> Database Buffers         3976200192 bytes

> Redo Buffers               14721024 bytes

> Database mounted.

> Database opened.

>

> RS: Swap is back to 7.32GB

> swap -s

> total: 7135384k bytes allocated + 191968k reserved = 7327352k used,

> 40566696k available

>

> RS: Still ISM..

>          Address     Kbytes        RSS       Anon     Locked Mode   Mapped

> File

> ...

> 0000000380000000    6422544    6422544          -    6422544 rwxsR    [ ism

> shmid=0x3000048 ]

>

> Even though, ISM is in use and sga_max_size is not in use, swap is

> allocated.

>

>

> Cheers

>

> Riyaj Shamsudeen

> Principal DBA,

> Ora!nternals -  http://www.orainternals.com

> Specialists in Performance, Recovery and EBS11i

> Blog: http://orainternals.wordpress.com

>

>

>

> On Sat, Aug 1, 2009 at 12:51 AM, Tanel Poder <tanel_at_poderc.com> wrote:

>

>> If you use ISM (when SGA_MAX_SIZE = SGA_TARGET or when SGA_MAX_SIZE is

>> unset in parameter file) then all SGA pages are locked in physical memory

>> (by OS VM design) - thus no swap space needs to be reserved as the pages in

>> memory aren't pageable.

>>

>> If you are using DISM (when SGA_MAX_SIZE > SGA_TARGET) then SGA is using

>> pageable large pages in Solaris (which are individually locked in physical

>> memory by Oracle's mlock requests). But as the pages are essentially

>> pageable, swap space needs to be reserved when SGA is created.

>>

>> If you want to avoid your SGA causing the swap space reservation, unset

>> your SGA_MAX_SIZE parameter.

>>

>> I have mentioned this on this blog entry (and in the comments section

>> there's a link to a Solaris kernel internals presentation):

>>

>>

>> http://blog.tanelpoder.com/2007/08/28/operating-systems-are-lazy-allocating-memory/

>>

>> --

>> Tanel Poder

>> http://blog.tanelpoder.com

>>

>>

>>

>> On Wed, Jul 29, 2009 at 7:31 AM, Crisler, Jon <Jon.Crisler_at_usi.com>wrote:

>>

>>>  On Solaris 10, when I start my databases, I see my swap space usage

>>> increase in a one for one ratio with memory utilization.   System has 64gb

>>> of memory.  If I start up a 4gb database, I see 4gb of real memory used and

>>> 4gb of swap space used up as well (as shown by top, swap –l, swap –s

>>> etc.).     This is purely a Oracle database server, and /etc/system and

>>> projects / resource controls seem to be set up, so I do not understand why

>>> swap is being touched.  If I stop all oracle processes, swap drops down to

>>> about 100 Mb used.

>>>

>>>

>>>

>>> I have taken great pains to make sure that NO swap is being used, yet any

>>> little allocation of Oracle gets tossed into swap.  I don’t know where to

>>> look after this- I would have suspected /etc/system or resource control /

>>> projects to be at fault, or /etc/security (ulimits) but everything looks

>>> ok.    The system has 64g real, and about 54 gb swap-  if I get close to

>>> 54gb memory allocated oracle will return out of memory errors..  Needless to

>>> say the system crawls.

>>>

>>>

>>>

>>> What am I overlooking ?  TOP and swap –s / swap –l agree so its not a TOP

>>> anomaly

>>>

>>>

>>>

>>> Example from TOP – I have 20g free, so why so much used in swap ?

>>>

>>>

>>>

>>> load averages:  0.64,  0.57,

>>> 0.46

>>> 00:26:34

>>>

>>> 1073 processes:1071 sleeping, 2 on cpu

>>>

>>> CPU states: 98.3% idle,  1.2% user,  0.5% kernel,  0.0% iowait,  0.0%

>>> swap

>>>

>>> Memory: 64G real, 20G free, 40G swap in use, 17G swap free

>>>

>>>

>>>

>>>    PID USERNAME LWP PRI NICE  SIZE   RES STATE    TIME    CPU COMMAND

>>>

>>>   1997 oracle     1  39    0 4376K 2592K cpu/50   0:02  0.04% top

>>>

>>>   3454 oracle     1  52    0   16G   16G cpu/32   0:00  0.03% oracle

>>>

>>>   3456 oracle     1  24    0   16G   16G sleep    0:00  0.03% oracle

>>>

>>>  18589 oracle     1  59    0   16G   16G sleep    0:13  0.02% oracle

>>>

>>>

>>>

>>> Swap –s

>>>

>>> total: 39170184k bytes allocated + 2262264k reserved = 41432448k used,

>>> 18017608k available

>>>

>>

>>

>>

>> --

>> Tanel Poder

>> http://blog.tanelpoder.com

>>

>>

>



-- 
Tanel Poder
http://blog.tanelpoder.com

--
http://www.freelists.org/webpage/oracle-l

Received on Sun Aug 02 2009 - 10:45:55 CDT