MEMORY_TARGET Not Supported on This System

I wasn’t aware, until this very moment, that there’s a strong correlation between the MAX_MEMORY_TARGET parameter and the ORA-00845: MEMORY_TARGET not supported on this system error. I thought that the MEMORY_TARGET is all that counts, considering that the actual memory allocation is based on this setting. However, apparently that’s not the case: Oracle will check the MAX_MEMORY_TARGET too and will complain if the value of this parameter cannot be honored by the available memory from the system.

The Proof

Let’s have a look on the following system:

[oracle@ion ~]$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              49G   20G   27G  43% /
tmpfs                 2.0G     0  2.0G   0% /dev/shm

As we can see, there are 2G of free shared memory in our tmpfs. Let’s configure our database with a MEMORY_TARGET of 1G and a MAX_MEMORY_TARGET of 4G.

SQL> alter system set memory_target=1G scope=spfile;

System altered.

SQL> alter system set memory_max_target=4G scope=spfile;

System altered.

Let’s restart the instance:

SQL> startup force
ORA-00845: MEMORY_TARGET not supported on this system

Ups, it doesn’t start up because the MEMORY_MAX_TARGET is set too high.

More Than One Database

If there are many databases running on the same host then things start to get interesting (kind of). I already have a database running:

[oracle@ion ~]$ ps aux | grep pmon
oracle    7161  0.0  0.4 1284760 19700 ?       Ss   12:21   0:00 ora_pmon_iondb

And the allocation in tmpfs is:

[oracle@ion ~]$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              49G   20G   27G  43% /
tmpfs                 2.0G  250M  1.7G  13% /dev/shm

Good! Let’s start the second database on the same host, using a MEMORY_MAX_TARGET of 1800M and a MEMORY_TARGET of 1500MB. I hand crafted these parameters into a customized init.ora file.

[oracle@ion ~]$ ORACLE_SID=iondb2 sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Mon Jul 21 12:55:45 2014

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup pfile='/home/oracle/init.ora'
ORA-00845: MEMORY_TARGET not supported on this system

Pretty obvious, but please note that the value of the MEMORY_MAX_TARGET is checked against the free available space from the tempfs, not against the total size of the tempfs. This is important to keep in mind, especially because Oracle doesn’t allocate the whole memory from the very beginning, which means that you might be able to startup both databases but, as they begin to allocate stuff in their own SGA, you might end up with this ORA-00845 error later.