Re: sga_max_size - pre-allocated at instance startup?

Laurenz Albe wrote:

>We asked specifically for AIX and the answer was: yes, all the shared
>memory in SGA_MAX_SIZE is allocated at instance startup, but only
>SGA_TARGET of it is actually used.

AIX is weird, see metalink on lock_sga and what _it_ requires, and it varies by version of everything.

Mladen Gogala wrote:

>As oracle uses the same POSIX IPC services across the whole range
>of Unix-like platforms, one can safely conclude that oracle will
>allocate all of the shared memory specified in the SGA_MAX_SIZE
>at the instance startup.

On hp-ux, I see it all being allocated on startup, even if startup screws up, sometimes leaving shared memory associated with a non-extant process, and not removable with ipcrm -m. Only reason I had to reboot with 6 month uptime (some processes were unable to get sockets).

Solaris and hp-ux have always implemented shared memory different from each other in my experience (back to SunOS 1.2 and hp-ux 9). Just because Posix has a service definition and ipc* have the same syntax doesn't mean things work the same, although they are getting closer in more recent Oracle.

Hey, I remember when posix was added to VMS and the joke was "VMS is more unix than unix."

jg

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