Comments on: Oracle 11g internals part 1: Automatic Memory Management http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/ Oracle troubleshooting, internals and performance tuning Mon, 15 Mar 2010 01:50:11 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: Tanel Poder http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-3882 Tanel Poder Thu, 18 Feb 2010 16:17:37 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-3882 <a href="#comment-3881" rel="nofollow">@Sherrie Kubis</a> Hi Sherrie, Replying here what I also said in ORACLE-L list: The memory which is reserved for PGA_AGGREGATE_TARGET will not show up in /dev/shm as it's not shared (PGAs are still allocated using process-private memory). You can query V$MEMORY_DYNAMIC_COMPONENTS to see how Oracle is currently using the memory: SQL> select component, current_size from v$memory_dynamic_components where component like '%Target%'; COMPONENT CURRENT_SIZE ------------------------------ ------------ SGA Target 545259520 PGA Target 293601280 Note that hugepages are not used with AMM on Linux so you may be not getting all the performance out of your hardware... @Sherrie Kubis
Hi Sherrie,

Replying here what I also said in ORACLE-L list:

The memory which is reserved for PGA_AGGREGATE_TARGET will not show up in /dev/shm as it’s not shared (PGAs are still allocated using process-private memory).

You can query V$MEMORY_DYNAMIC_COMPONENTS to see how Oracle is currently using the memory:

SQL> select component, current_size from v$memory_dynamic_components where component like ‘%Target%’;

COMPONENT CURRENT_SIZE
—————————— ————
SGA Target 545259520
PGA Target 293601280

Note that hugepages are not used with AMM on Linux so you may be not getting all the performance out of your hardware…

]]> By: Sherrie Kubis http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-3881 Sherrie Kubis Thu, 18 Feb 2010 13:49:27 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-3881 Tanel, thanks for publishing this, you are shedding light on how our Linux RAC Clusters are working. Question: We have a 3-node (each 32gb ram) Linux RAC cluster running Oracle 11.1.0.7, housing 4 instances with a total memory_target of 8.75 gb. OEM shows 29% ram is used. We are using AMM. The free -mt command shows total used free shared buffers cached Mem: 32189 31519 669 0 1250 25168 -/+ buffers/cache: 5101 27088 Swap: 32767 39 32728 Total: 64957 31559 33397 It looks like tmpfs is 16gb: df -k /dev/shm Filesystem 1K-blocks Used Available Use% Mounted on tmpfs 16481056 5604532 10876524 35% /dev/shm It looks like we are seeing 5.6gb of memory used, so I'm confused about why our sgas are defined to consume 8.75gb, but we only see 5.6gb used. read that the sga by default takes 60% of memory_target and pga gets the rest. Because there are not many connections, is this why we see a lower value? Does the tmpfs at 16gb mean we can only use 16gb of ram for our databases? We are just getting up and running, so there are not yet many connections. I Any insights would be appreciated. Tanel, thanks for publishing this, you are shedding light on how our Linux RAC Clusters are working. Question: We have a 3-node (each 32gb ram) Linux RAC cluster running Oracle 11.1.0.7, housing 4 instances with a total memory_target of 8.75 gb. OEM shows 29% ram is used. We are using AMM. The free -mt command shows
total used free shared buffers cached
Mem: 32189 31519 669 0 1250 25168
-/+ buffers/cache: 5101 27088
Swap: 32767 39 32728
Total: 64957 31559 33397

It looks like tmpfs is 16gb:
df -k /dev/shm
Filesystem 1K-blocks Used Available Use% Mounted on
tmpfs 16481056 5604532 10876524 35% /dev/shm

It looks like we are seeing 5.6gb of memory used, so I’m confused about why our sgas are defined to consume 8.75gb, but we only see 5.6gb used. read that the sga by default takes 60% of memory_target and pga gets the rest. Because there are not many connections, is this why we see a lower value?

Does the tmpfs at 16gb mean we can only use 16gb of ram for our databases?

We are just getting up and running, so there are not yet many connections. I
Any insights would be appreciated.

]]> By: Don Woods http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-3664 Don Woods Wed, 20 Jan 2010 04:52:17 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-3664 Tanel, Thank you for your excellent analysis and summary of Oracle 11g memory management. I am installing 11g on a new Sun server and could not figure out why I received memory allocation errors when the SGA was increased to more than 4GB. Your experience has saved me countless hours of work. --Don Tanel, Thank you for your excellent analysis and summary of Oracle 11g memory management. I am installing 11g on a new Sun server and could not figure out why I received memory allocation errors when the SGA was increased to more than 4GB.

Your experience has saved me countless hours of work.

–Don

]]> By: Tanel Poder http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-2879 Tanel Poder Sun, 01 Nov 2009 16:39:53 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-2879 Glad to be useful! Glad to be useful!

]]> By: jni http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-2878 jni Sun, 01 Nov 2009 16:34:18 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-2878 Well mate, that blog just saved me hours of researching. Thanks alot for sharing! Awesome blog! Well mate, that blog just saved me hours of researching. Thanks alot for sharing! Awesome blog!

]]> By: Hind http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-1625 Hind Sun, 24 May 2009 07:51:43 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-1625 thanks, a note to say: add this entry to /etc/fstab to mount shm every boot tmpfs : /dev/shm tmpfs size=2500m 0 0 thanks, a note to say:
add this entry to /etc/fstab to mount shm every boot tmpfs :
/dev/shm tmpfs size=2500m 0 0

]]> By: Uma http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-1242 Uma Sat, 21 Mar 2009 01:48:43 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-1242 Hello there, Thank you for all the info. I am very new to oracle 11g install on linux, tried to recover a db (created using dbca) using rman, ran into error,when tried to do startup mount, got the error described here, I am trying to implement the solution given by you, tried to umount /dev/shm- got the error device is too busy, does this mean I have to shut down the db and then try to unmount? Can you please help? Many thanks in anticipation. Hello there,
Thank you for all the info.
I am very new to oracle 11g install on linux, tried to recover a db (created using dbca) using rman, ran into error,when tried to do startup mount, got the error described here, I am trying to implement the solution given by you,
tried to umount /dev/shm- got the error device is too busy,
does this mean I have to shut down the db and then try to unmount?
Can you please help? Many thanks in anticipation.

]]> By: Blaine Simpson http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-1111 Blaine Simpson Wed, 04 Mar 2009 15:36:51 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-1111 Most users probably want the shm size adjustment to persist across reboots. So, here's the /etc/fstab entry corresponding to Tanel's mount command above: none /dev/shm tmpfs size=1300M 0 0 (My very healthy OpenSUSE 11.1 system has no /dev/shm fs set up at all by default). Run "mount /dev/shm" to mount it on-demand. Most users probably want the shm size adjustment to persist across reboots. So, here’s the /etc/fstab entry corresponding to Tanel’s mount command above:

none /dev/shm tmpfs size=1300M 0 0

(My very healthy OpenSUSE 11.1 system has no /dev/shm fs set up at all by default). Run “mount /dev/shm” to mount it on-demand.

]]> By: Tanel Poder http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-1057 Tanel Poder Thu, 26 Feb 2009 05:59:36 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-1057 Hi Kirk, no official part-2 yet, here are the posts which I've tagged as related to 11g: http://blog.tanelpoder.com/category/oracle-11g/ Hi Kirk, no official part-2 yet, here are the posts which I’ve tagged as related to 11g:

http://blog.tanelpoder.com/category/oracle-11g/

]]> By: Kirk Brocas http://blog.tanelpoder.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/comment-page-1/#comment-1055 Kirk Brocas Thu, 26 Feb 2009 00:40:03 +0000 http://tanelpoder.wordpress.com/2007/08/21/oracle-11g-internals-part-1-automatic-memory-management/#comment-1055 Is there a part 2? Is there a part 2?

]]>