lock_sga on AIX 5L

AIX 5.3 ORA-27126: unable to lock shared memory segment in core

when setting lock_sga=true

This doesn’t appear to be documented many places, so I’ll put it here. There can be a tangible performance increase to ‘locking’ SGA to pinned memory. Paging spaces are, after all, on a slower medium (disk). In AIX 5.3 you also need to ‘pin’ shared memory. (SGA is shared memory)

First, you’ll need to set the ‘vmo’ option v_pinshm to 1. This tells AIX to ‘pin’ shared memory into RAM.

Second, you’ll need to give the ‘oracle’ user (or whatever user the database runs as) the following capabilities:

CAP_BYPASS_RAC_VMM and CAP_PROPAGATE

The commands to do this (as root on the system) are as follows:

***To set v_pinshm***
# vmo -p -o v_pinshm=1


***To give the "oracle" user the necessary capabilities***
# chuser capabilities=CAP_BYPASS_RAC_VMM,CAP_PROPAGATE oracle

large memory pages may also help too

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