ORA-00845 Raised When Starting Instance (文檔 ID465048.1)

ORA-00845 Raised When Starting Instance (文檔 ID465048.1)

APPLIESTO:                                                    

OracleDatabase - Enterprise Edition - Version 11.1.0.6 and later

OracleDatabase - Standard Edition - Version 11.2.0.1 to 11.2.0.1 [Release 11.2]

Linuxx86

Linuxx86-64

***Checkedfor relevance on 30-Sep-2014***

SYMPTOMS                                                      

Duringthe startup of the database instance the following error is raised:

SQL>connect sys as sysdba

Enterpassword: *****

Connectedto an idle instance.

SQL>STARTUP NOMOUNT

ORA-00845:MEMORY_TARGET not supported on this system

Theinstance alert file shows:

StartingORACLE instance (normal)

WARNING:You are trying to use the MEMORY_TARGET feature.

Thisfeature requires the /dev/shm file system to be mounted for at Least<size> bytes.The /dev/shm is either not mounted or is mounted withavailable space less than this size.

Pleasefix this so that MEMORY_TARGET can work as expected. Current available is<size> and used is <size> bytes.memory_target needs larger /dev/shm

Alsoerror messages like ORA-4031 may be reported and no new connections can beestablished to the database.

CHANGES                                                        

TheAutomatic Memory Management (AMM) has been implemented by setting parameterslike MEMORY_TARGET and/or MEMORY_MAX_TARGET.

CAUSE                                                          

Thenew Automatic Memory Management functionality uses /dev/shm on Linux for SGAand PGA management. The errors occur if either MEMORY_TARGET orMEMORY_MAX_TARGET is configured larger than the configured /dev/shm size, or if/dev/shm is mounted incorrectly.

SOLUTION                                                       

Pleaseconfirm that ORACLE_HOME is set correctly. This error sometimes happens when itis not set correctly.

Makesure that the /dev/shm size is configured large enough, like in:

#mount -t tmpfs shmfs -o size=7g /dev/shm

Inthis case, the size of the shared memory device is configured to be 7GB.

Inorder to make the same change persistent across system reboots, add an entryfor this to the /etc/fstab mount table, as in:

shmfs/dev/shm tmpfs size=7g 0

Note:                                                          

Youshould check with your System Administrator what the "best" size for/dev/shm is, based on what has been reported in the alert file.

Also,many best practices now suggest disabling AMM especially in Exa* Engineeredboxes that have larger memory capability and can use Huge / Large pages.

Thisis because AMM and Huge / Large pages are mutually exclusive and overallperformance will be better using Huge pages

Makesure that the df output shows the correct /dev/shm configuration when usingOracle on the system:

$ df-k

Filesystem1K-blocks Used Available Use% Mounted on

...

shmfs6291456 832356 5459100 14% /dev/shm

REFERENCES                                                     

NOTE:361323.1- HugePages on Linux: What It Is... and What It Is Not...