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i have at customer side a server (win2003 R2 SP2 standard edition 32-bit) with a sql-server 2005 and some databases. This system starts with the /3GB-Switch. The system reports 3.25 GB RAM and taskmanager reports the process of sqlserver.exe with 2758255 K as the process with the highest consumption.

The OS separates RAM for applications and for itself, normaly 50:50. But here we have the /3GB-Switch aktivated and i think the part for the applications is more than 50% of RAM.

Knowledge (or better not knowledge):

Somebody told me that if the OS runs out of memory within his part of RAM, the server runs into pressing mode.

Questions:

  • What is this pressing mode?

  • Is pressing mode possible at all in this szenario?

  • What should be done to get more performance out of this sql-server, beside optimizing the database and all this stuff.

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migrated from superuser.com Jan 14 '10 at 15:06

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4 Answers

Never heard about this "pressing mode", and Google can't seem to find nothing about it; howewer, this could actually be a problem, but usually it isn't.

It's quite difficult for the kernel to actually use up a whole GB of memory; this could happen with memory-intensive device drivers, or if you also enable the /PAE switch, which induces increased memory management overhead.

The best option here would be switching to x64 Windows; even if you only have 4 GB of physical memory, you could at least use all of them and not need to worry about kernel/user space issues anymore. You're using SQL Server 2005, so this is a viable option (unless you have other application issues).

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it's not tht the kernel uses up 1 GB of memory but that you run out of the ability to manage the other 3gb of ram. Tthese are called free page table entries and it's usually the first problem you run into when running apps when you've turned on the 3gb switch (which typically show up as I/O request failures). All the details are in my answer. –  Jim B Jan 15 '10 at 2:49
    
Yes, I was referring exactly to that with the expression "increased memory management overhead"; I've seen a 18-GB server literally agonizing after enabling both /3GB and /PAE. It shouldn't be a problem with 4 GB and no /PAE, though. –  Massimo Jan 15 '10 at 8:18
    
Of course, x64 is the way to go here. –  Massimo Jan 15 '10 at 8:21
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I've never heard of "pressing mode" but you can read more than you probably want to know about windows memory handling in this answer. The first thing I'd do to optimize this server is see if you can get the system rebuilt as 64 bit.

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You sure that the one who told you about this "pressing" mode didn't actually call that thing "paging"?

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Or "thrashing", maybe... –  Massimo Jan 14 '10 at 21:11
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up vote 0 down vote accepted

thanks for your attention. i regrett my humble question but the problem is described om the following blog. http://blogs.msdn.com/slavao/archive/2006/11/13/q-a-does-sql-server-always-respond-to-memory-pressure.aspx

I found it in neverending research and it's exact what i meant.

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