Re: Oracle memory allocation on Linux 2.6

On Wed, 02 Apr 2008 03:20:27 -0700, vitalisman wrote:

> On 9i, filesystemio_options=none (default) and Oracle binaries are not
> linked for AIO (default, at least with RAC). I'm in the process of
> testing AIO and DIO on RAC 9i following Oracle support questions, but
> the first attempts gave way to some instance internal errors... I've
> asked the support if this is really a supported configuration (at least
> with OCFS1, it was not, apparently.)
>
> Thanks Mladen for your answer!

Jerome, direct I/O should lower memory consumption simply because it bypasses buffer cache over which we have no control. you still can control the amount of consumed memory through

• min_free_kbytes,
• dirty_background_ratio,
• dirty_expire_centisecs
• dirty_writeback_centisecs.

You cannot control the size of cache components (like buffer cache) but you can control behavior and overall limit with min_free_kbytes. It's essentially the same approach as the one taken by oracle. You can determine an overall lump of memory that you want to use, but not the structure of that lump. The structure will be adjusted by some AI predictive component of the software. So far, the "I" part is failing miserably in both cases. With Linux, I really have a problem with the "OOM killer" component. I cannot see how would that be superior to the traditional mechanisms for fine-tuning the memory allocation. I used to work on an ancient and arcane OS, the best one I've ever seen, called "VAX/VMS". I started with the version 4.2 and the last version that I used was 5.5-2. Believe it or not, VAX/VMS used to have far superior monitoring tools and memory tuning mechanisms to any of modern Unix systems. Linux systems are far inferior to things like AIX 5.3, HP-UX 11.11 or Solaris 10 and those systems are, in turn, far inferior to VAX/VMS. I believe that the root of the evil is in the crusade against expensive administrators. DBA personnel, as well as system administrators are considered "expensive" and disliked by the modern management. Just as there is a tendency to cut the number of expensive workers in automobile industry, there is also a tendency to replace everybody by "business professionals", people programming with Hibernate and Tapestry for WebLogic or JBoss, knowing next to nothing about databases or the underlying OS. That's the real spirit of Windows platform, as well as the Linux platform. If I understand the business correctly, what is wanted is the system that can be used and administered by Elbonians. Fortunately for us, the effect is precisely the opposite. Oracle11 is the most complex database to date and Linux 2.6 is the most problems-prone Linux version ever. You need better administrators than ever, fewer and fewer are up to the task. I will not shed a tear over a demise of Linux, when that happens. However, don't be mistaken: the industry will succeed, eventually. They succeeded in the automobile industry, there is no reason to doubt the progress and the prospect of the ultimate victory for idiots. HAL 9000 awaits us.

-- 
Mladen Gogala
http://mgogala.byethost5.com