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

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@xxxxxxxxxx> 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@xxxxxxx> 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
>
>

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