Performance Testing, LoadRunner Tips&Tricks

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Monitors: Memory Glossary

This is a compilation of memory-related counters. Do feel free to revert or comment should you have additional information on the counter.


Available Bytes
  • Process Working Set growth becomes constrained when Available Bytes <>

Pool Nonpaged Bytes
  • The system’s non-pageable (fixed) memory.


Pool Paged Resident Bytes
  • The OS‘s pageable memory that is currently resident in RAM.


System Code Resident Bytes
  • [Coming soon]


System Driver Resident Bytes
  • Total System Resident Bytes = Pool Nonpaged Bytes + Pool Paged Resident Bytes + System Code Resident Bytes + System Driver Resident Bytes + System Cache Resident Bytes.


System Cache Resident Bytes
  • The current amount of RAM used for the file cache.


Page Faults/sec
  • Can be a grossly misleading number. Page Faults/sec = “soft” Transition Faults + application file Cache Faults + demand zero faults + hard page faults.


Page Reads/sec
  • This counter measures the number of requests to the I/O manager to retrieve pages of memory from the disk. Despite the name of this counter, it measures requests, not pages; a request can be for more than a single page.
  • Equivalent to hard page fault rate.


Page Writes/sec
  • This counter measures the number of requests to the I/O manager to write pages of memory to the disk. Again, each request can be for more than a single page.
  • Updated “dirty” pages must be flushed to disk before they can be reused by a different application.


Pages Input/sec
  • This counter measures the number of pages read from the disk per second. Combing this counter with the Page Reads/sec counter can tell you how many pages are retrieved per request.
  • Calculate the bulk paging rate: Pages Input/sec / Pages Read/sec


Pages Output/sec
  • This counter measures the number of pages written to the disk per second. Combining this counter with the Page Writes/sec counter can tell you how many pages are written per request.
  • Try to limit Pages Input/sec + Pages Output/sec to 10 – 20% of total disk bandwidth, if possible. Disk bandwidth absorbed for paging operations is unavailable for application processes.


Pages/sec
  • This counter measures the total number of pages read and written to the disk. This counter represents the sum of Pages Input/sec and Pages Output/sec. Using this counter along with the Disk Bytes/sec counter from the Physical Disk Object, you can determine what portion of the data transferred to the disk is due to memory access, and what portion is due to file system access.


Committed Bytes
  • Represents virtual memory pages backed in either RAM or secondary storage (paging files). Calculate a virtual: real memory contention index = Committed Bytes / Total RAM. Consider adding RAM when this ration starts to approach 2:1.


Commit Limit
  • Maximum number of virtual memory pages that can be allocated without extending the paging file(s).


% Committed Bytes in Used
  • Committed Bytes / Commit Limit. Consider adding RAM when consistently > 70% on a server.


Cache Bytes
  • Actually, the system address space working set, but includes the file cache. The sum of Pool Paged Resident Bytes + System Code Resident Bytes + System Driver Resident Bytes + System Cache Resident Bytes.


Transition Faults/sec
  • “Soft” page faults resolved without having to access the disk.


Cache Faults/sec
  • Normal application file I/O operations are diverted to use the paging subsystem. Each file cache fault leads to a physical disk read I/O operation.


Demand Zero Faults/sec
  • The rate at which applications require brand new pages.


Write Copies/sec
  • Private Copy on Write pages from shared DLLs.


Pool Paged Bytes
  • Calculate a virtual: real memory contention index = Pool Paged Resident Bytes / Pool Paged Bytes. Compared to Page Reads/sec to anticipate real memory bottlenecks.



Related Topics

Content Page - General
Content Page - Monitors
Monitors: What metrics/counters to monitor for Windows System Resource?
Virtual Addressing
Page Fault Resolution
Page Fault Resolution (Illustration)
Performance Concerns
Virtual Memory Shortage Alerts
Available Bytes
LRU
System Working Set
Detecting Memory Leaks
Measuring Memory Utilization

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