Re: hugepages question

Now that you have re-created the database, if you shut it down and start it up does it still raise that error (assuming use_large_pages=ONLY)?

A *guess* I have is that your memlock for the oracle user in /etc/security/limits.conf is too low, like lower than the number of bytes you have reserved via the vm.nr_hugepages parameter. So for example, the output from this:
grep nr_hugepages /etc/sysctl.conf

tells you how many huge pages you have allocated, which are 2MB each. So your vm.nr_hugepages times 2MB times 1024kB will give you your huge pages in kilobytes. That must be less than your oracle user memlock limit (kB) from this:
grep memlock /etc/security/limits.conf
(if it's not set in there, 'ulimit -l' will show you what it is defaulting to instead)

If memlock is too low, the oracle user cannot lock enough physical memory into its address space, which is a requirement for allocating huge pages. In your case, my guess would be that as soon as you shut the clone database down, it freed some space within the memlock limit and something else that is not huge pages took it. You can set the oracle user memlock limit 'unlimited' or at or near the amount of physical memory on the server to solve this.

There are other things that I can think of, but it matters what is going on with the other databases: their use_large_pages and pre_page_sga settings, their sga_target and sga_max_size settings, plus the amount of physical memory on the server and your vm.nr_hugepages setting. Generally speaking, you want sga_target=sga_max_size and the sum of all the sga_targets must be less than the huge pages you have reserved via vm.nr_hugepages.

Andy

On Wed, Feb 13, 2019 at 6:11 PM Jeff Chirco <backseatdba_at_gmail.com> wrote:

> Ok I just recently enabled hugepages on Production and Development.
> Everything is going good but I noticed that on my development environment
> which consists of a bunch of thin clones, when I remove and recreate the
> same clone the database fails to create, I am getting:
>
> ORA-27137: unable to allocate large pages to create a shared memory segment
>
> I have the parameter *use_large_pages=ONLY*
> So it makes sense I would get this error when there is not enough pages.
> However I just removed this same database and am recreating it. I would
> think that would free it up but apparently not. Does pages not get
> released immediately when a database is removed? Is there something I
> should run to free it? Or just not have use_large_pages=ONLY and leave it
> at TRUE on Dev? I had to set it to TRUE to get this database up.
>
> Thanks,
> Jeff
>

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