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Don Burleson Blog 







VMware: Optimizing Linux

Oracle Tips by Burleson Consulting

With today's cheap hardware costs, it is safe to assume a virtual server host will have multiple processors and lots of memory, most likely greater than 4 GB. And since the virtual server host is the relative center of the universe so to speak, it therefore cannot offer up to clients anything which it cannot itself do or access. So you need to go with 64-bit Linux unless you face some hardware driver issue that prevents this choice.

There is one more little tweak that should be applied to any 64-bit Linux server with significant memory and that is the use of huge pages. This is Linux 2.6 kernel feature simply utilizes larger than the 4K pages to reduce virtual memory I/O operations when working with lots of memory. Here are some documented limits:

Hardware Platform

Kernel 2.4

Kernel 2.6

Linux x86 (IA32)



Linux x86-64 (AMD64, EM64T)



Linux Itanium (IA64)



IBM Power Based Linux (PPC64)



IBM zSeries Based Linux



IBM S/390 Based Linux



The process to enable huge pages is as follows:

  • X = grep Hugepagesize /proc/meminfo

  • Y = Largest (MB of all client SGAs) * 1024

  • Z = # Huge Pages needed = Y / X

  • Set Huge Page Pool size

edit /etc/sysctl.con
vm.nr_hugepages = Z

  • Increase ulimit parameter memlock for oracle user

    • edit /etc/security/limits.conf

    • oracle soft   memlock      Y

    • oracle hard  memlock      Y

  • reboot

To improve I/O for file system requests made by the hosted clients and/or their databases, Linux offers a little known and seldom used option that can yield between 50-150% performance improvements in standard database benchmarks like the TPC-C by simply changing the /etc/fstab file entries for the Oracle data file mount points as follows:

  • For ext2 and 3 file systems, add ,noatime to the third column.

What this does is tell the operating system that it is not necessary to update the last access time for directories and files under that mount point, which translates into radically reduced total I/O. Since the host file system is simply a mechanism to provide abstracted storage to its clients, why spend I/O resources to update time attributes for files or directories? Especially when it is fairly unlikely you will ever access them via the host for any reason other than maybe doing backups.

The one last item to consider for optimizing Linux on your virtual server host is to compile a monolithic kernel, which is nothing more than the kernel compiled to only load those features you must have and not load those that are unnecessary. However, you better be comfortable with compiling, linking and installing a new kernel lest you goof up your Linux install. (Not really, but I want readers to be very sure before going this route!) It consists of just the following rather easy steps:

  • cd /usr/src/linux or /usr/src/kernels/xxx where xxx is the kernel source version

  • make mrproper (simply cleans up under that directory tree)

  • make config or xconfig (if Linux install supports X-Windows)

  • answer all the questions on what to compile or load into the resulting kernel and what not to thus reducing its size, memory footprint and complexity

  • make dep; make clean; make bzImage

  • cp/usr/src/linux/arch/i386/boot/bzImage/vmlinuz-kernel.version.number

  • cp/src/linux/ kernel.version.number

  • edit/boot/grub/grub.conf

 have image= point to new kernel version binaries

The only other item that you might consider for optimization is to recompile and relink the C runtime library with more optimistic compiler optimization directives. But this step requires perfect execution since any failure along the way means a total reinstall of the Linux OS. Therefore, I generally advise most people not to attempt this step although it has been known to yield significant performance improvements for those who can successfully complete it.

This is an excerpt from
Oracle on VMWare: Expert tips for database virtualization by Rampant TechPress.


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