[CentOS] CENTOS 4.7 or 5.2 32 bits O.S. for ORACLE DB server??

Adam Tauno Williams awilliam at whitemice.org
Fri Jan 16 16:57:45 UTC 2009


> mcclnx mcc wrote:
> > we plan to setup our ORACLE database server (32 bits DB) and use dell
> > r900 server.  This server can put up to 128GB RAM.
> > We are thinking use 32 bits CENTOS 4.7 or 5.2.  My concern about
> > CENTOS 5.2 is it only support up to 16 GB RAM on 32 bits O.S.
> > Any suggestion?
> To get beyond 4 GB of RAM with a 32-bit Intel CPU, you have to turn on
> PAE mode, which is a very ugly hack, invented several years ago now.  It
> dates back to the old Pentium Pro!  It was created before inexpensive
> 64-bit CPUs were available.  Systems being built today should not use
> PAE mode, IMHO.  If you need more than 4 GB of RAM today, use a 64-bit
> OS and applications.  That will let you address the full memory
> capability of that server.
> In PAE mode, the system runs a little slower due to the extra overhead
> of the more complicated memory management scheme, and it can't really
> address that 16 GB all at once.  It's kind of a like the old DOS days
> when we had 32-bit CPUs but could only address 64 KB of memory at a
> time, and could only access 640 KB without resorting to PAE-like hacks
> called EMS and XMS.  These workarounds are best consigned to the dustbin
> of history.

Not true.  The comparison of PAE to EMS/XMS is completely bogus, the
technologies aren't alike at all.  PAE does *NOT* involve any bank
switching; a system using PAE can "address that 16 GB all at once".
Comparing PAE to EMS/XMS has the same level of validity as comparing
a .NET or Java virtual machine to a shell script interpreter.

<http://en.wikipedia.org/wiki/Physical_Address_Extension#Page_table_structures>

There is a, usually very small, performance penalty to PAE due to the
using a three level verses a two level page directory.



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