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  1. Documentation
  2. DOCS-491

Working-set calculation, RAM, oplog, non-mapped memory, and faults

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    • Resolution: Done
    • Icon: Major - P3 Major - P3
    • Server_Docs_20231030
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    Description

      Based on customer interaction, it seems we need a better doc than this one for calculating how much RAM you need for your app:

      http://www.mongodb.org/display/DOCS/Checking+Server+Memory+Usage#CheckingServerMemoryUsage-WorkingSetSize

      I think there's some useful verbiage in my responses to CS-4233, and probably scattered all over in a million answers from 10gen staff to questions over the years of the form, "Do I have enough RAM?"

      Here are the points I think we should hit:
      *) Relationship b/w db storage and working set
      *) OS's LRU cache strategy
      *) Impact of journaling
      *) Using page faults and other MMS gauges to detect when you need more RAM
      *) What is non-mapped memory? It's basically a linear function of connection count.
      *) The oplog can be ignored when calculating working set (for some reason, that customer thought it was especially important when the opposite is true)

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            bgrabar Bob Grabar
            jesse@mongodb.com A. Jesse Jiryu Davis
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            Dates

              Created:
              Updated:
              Resolved:
              11 years, 6 weeks, 4 days ago