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  1. Core Server
  2. SERVER-2793

Understanding memory/disk metrics

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    • Icon: Question Question
    • Resolution: Done
    • Icon: Major - P3 Major - P3
    • None
    • 1.6.5
    • Performance
    • None
    • Ubuntu 10.04

    Description

      I'm trying to delve deeper into MongoDB memory/disk usage patterns to both optimize my configuration and to identify warning signs for impending performance problems. I have some high level questions first:

      • mongod resident memory: I generally don't see this go above half the available RAM. Any idea what causes resident memory size to grow vs pages just sticking in the OS file cache?
      • Is there any way to distinguish between memory warming up and an actual memory crunch? Any metrics/ratios to look out for in tools like iostat, sar, vmstat, etc.?
      • Are there any metrics you look at to indicate that RAM is nearly full? I'm graphing most metrics in "/proc/meminfo" over time, however, when it appears I've hit my RAM threshold, things like active RAM in /proc/meminfo is reported at only half of RAM. Inactive is the other half.
      • Shouldn't the amount reported as "Mapped" in /proc/meminfo be a comprehensive number that indicates how much MongoDB has mapped and therefore how much memory it's using?

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            gatesvp Gaetan Voyer-Perrault
            charso charso
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