32Bit Windows Memory Tuning 101

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32-Bit WindowsMemory Tuning 101

• 80/20 Performance Tuning

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Agenda

• Foundations of 32-bit computing
• How to indentify memory constraints
• Possible solution

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32-bit Foundations

• Using 32-bits to address memory yields 232 or
  4,294,967,296 addresses a 4GB address limit.
• This limit shows up in several places in 32-bit
  Windows and is sometimes modifiable.

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Base Operating System

• 32-Bit Windows will only see 4 GB of system
  memory by default.
• Adding the /PAE switch to boot.ini will enable
  all physical memory up to the OS limit

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Processes

• A single process is subject to the 4 GB address
  limit
• Windows defaults to 2 GB for system space and 2
  GB for user space per-process.

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Modifying Process Profile /3gb

• Adding the /3GB switch to boot.ini will change
  the default process memory allocation
• Your App has to recognize and be able to use /3GB
• Impacts the OS Processes

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/PAE /3GB Together

• Limits OS to 16GB
• Impacts the System Free Page Table Entries

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Modifying Process Profile /awe

• /AWE avoids the 16GB limit seen with /PAE /3GB
• AWE enables programs to reserve physical memory
  as non-paged memory and then to dynamically map
  portions of the non-paged memory to the program's
  working set of memory (e.g. SQL)
• App must be coded to use /AWE

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Identifying Bottlenecks

• Task Manager (quick-check)
• Perfmon (is your friend)

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Task Manager
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Perfmon

• PerfMon and PerfLog report on all
  Performance-enabled apps
• Has embedded explanations for all system counters

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Possible Solutions(When do I add memory)

• When Server has less than 4GB and Commit Charge
  is constantly greater than Physical (Task Mgr)
• When 1 and App generates lots of processes go
  above 4GB (JVMs)
• When 1 and App is coded for /3GB or /AWE

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Links

• http//support.microsoft.com/search
• http//support.microsoft.com/kb/291988/en-us
• http//www.microsoft.com/whdc/system/platform/serv
  er/pae/paedrv.mspx
• http//support.microsoft.com/kb/823440/en-us
• http//blogs.technet.com/askperf/archive/2007/02/2
  3/memory-management-101.aspx