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New Up to 1GB under 2.4 kernel
But its limited to the value of SHMMAX with which the kernel was compiled. SHMMAX is defined in shmparam.h.

However, if I read the docs correct, this value is the per-segment limit, not the grand total. The number of segments is capped by SHMALL. So if your DB can be taught to allocate more than one segment you can avoid recompiling.
I have SHMMAX set to 32 meg and SHMALL set to 256 meg. I'll take a look at the .h file.

We may remove some of the 486 code from the kernel to make it smaller, too, if we decide to recompile.


Glen Austin
New linux/shm.h for i386
It seems not all architectures store SHMMAX in shmparam.h. For i386, they are defined in linux/shm.h instead. I didn't have all the kernel sources handy earlier. Sorry for the wild goose chase.

But the documentation does seem to conflict. shm.h gives the impression that SHMMAX is a default which can be adjusted through sysctl; the kernel docs claim its the max. segment size.
     Shared Memory Limitations in Linux - (gdaustin) - (3)
         Up to 1GB under 2.4 kernel - (scoenye) - (2)
             SHMMAX, SHMALL - (gdaustin) - (1)
                 linux/shm.h for i386 - (scoenye)

Hey, it was good enough for Terry Pratchett.
126 ms