Hi List,

I’m tuning up a new database server and I’m finding very mixed information online.

Here are the default shmmax and shmall from my new system

cat /proc/sys/kernel/shmmax
4294967295

cat /proc/sys/kernel/shmall
268435456

SHMALL is close enough to being SHMMAX / 16.

Now, everything I’m finding online tells me that SHMALL = SHMMAX /
PAGE_SIZE. default page size is 4096.

Has something changed in this calculation? should the defaults be set on SHMALL = SHMMAX / 16??

I’m running CentOS Linux release 7.1.1503 (Core), my old database is running CentOS release 6.6 (Final) and I’m seeing the same calculations there too.

Can somebody please point me in the right direction, I’ve had a look at pgtune here http://pgtune.leopard.in.ua/, I will not be using the
‘default’ calculated configuration that it suggests but I noticed the shmall = shmmax / page_size (4096).

I’ll benchmark with both calculations but I would really appreciate some confirmation on this.

thanks

Michael