Call now: 252-767-6166  
Oracle Training Oracle Support Development Oracle Apps

 E-mail Us
 Oracle Articles
New Oracle Articles

 Oracle Training
 Oracle Tips

 Oracle Forum
 Class Catalog

 Remote DBA
 Oracle Tuning
 Emergency 911
 RAC Support
 Apps Support
 Oracle Support

 SQL Tuning

 Oracle UNIX
 Oracle Linux
 Remote s
 Remote plans
 Application Server

 Oracle Forms
 Oracle Portal
 App Upgrades
 SQL Server
 Oracle Concepts
 Software Support

 Remote S


 Consulting Staff
 Consulting Prices
 Help Wanted!


 Oracle Posters
 Oracle Books

 Oracle Scripts

Don Burleson Blog 









Oracle shared memory parameters for UNIX/Linux

Oracle Database Tips by Donald Burleson

Oracle MOSC Note 15566.1 Unix Semaphores and Shared Memory Explained, has a great summary of Oracle kernel related UNIX/Linux parameters:

System Parameters
SHMMAX - kernel parameter controlling maximum size of one shared memory
SHMMHI - kernel parameter controlling maximum number of shared memory segments
         in the system
SHMSEG - kernel parameter controlling maximum number of shared memory segments
         a process can attach
SEMMNS - kernel parameter controlling maximum number of semphores in
         the system
SEMMNI - kernel parameter controlling maximum number of semaphore
         sets.  Semphores in Unix are allocated in sets of 1 to SEMMSL.
SEMMSL - kernel parameter controlling maximum number of semaphores in a
         semphore set.
SHMLBA - kernel parameter controlling alignment of shared memory
         segments; all segments must be attached at multiples of this value.
         Typically, non-tunable.
Oracle UNIX/Linux parameters:
SS_SEG_MAX - Oracle parameter specified at compile time (therefore,
             unmodifiable without an Oracle patch) which defines maximum
             number of segements the SGA can reside in.  Normally set to 20.
SS_SEM_MAX - Oracle parameter specified at compile time (therefore,
             unmodifiable without an Oracle patch) which defined maximum
             number of semaphore sets oracle will allocate.  Normally set to 10.

        Recommended Semaphore and Shared Memory Parameters 
Operating System        Shared Memory Parameters                 Semaphore 
----------------        ------------------------                 --------- 
Sun OS                  SHMSIZE = 32768                          SEMMNS = 200 
                        SHMMNI = 50                              SEMMNI = 50 
Solaris                 SHMMAX = 8388608(or larger than max SGA) SEMMNS = 200 
                        SHMSEG = 20                              SEMMSL = 50 
                        SHMMNI = 100                             SEMMNI = 70 
HP/UX                   SHMMAX = 0x4000000 (64 Mb)               SEMMNS = 128 
                        SHMSEG = 12                              SEMMNI = 10 
If you like Oracle tuning, you may enjoy my new book "Oracle Tuning: The Definitive Reference", over 900 pages of BC's favorite tuning tips & scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



Oracle Training at Sea
oracle dba poster

Follow us on Twitter 
Oracle performance tuning software 
Oracle Linux poster


Burleson is the American Team

Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  

and include the URL for the page.


Burleson Consulting

The Oracle of Database Support

Oracle Performance Tuning

Remote DBA Services


Copyright © 1996 -  2017

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.

Remote Emergency Support provided by Conversational