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I'm currently investigating why I didn't get notified about a high memory utilization on one RHEL server from dynatrace. When checking the graphs of memory usage, both sar and dynatrace show different results.
On SAR it is showing that the server is using 90% for about 11 hours, here's the screenshot of that:

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And on the same day this is what dynatrace shows:

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And as you can see they are both from May 3 2024. The metric they are using is memory usage %. I'm very confused about these two graphs, I'm not an expert on sar so maybe I'm missing something else, if somebody could help me to find out if I'm missing something that will be very appreciated!

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The reason for displaying different graphs is that both tools just do not achieve the same calculus when estimating memory usage.

With regards to labels & values as taken from /proc/meminfo,

dynatrace is reported using the following formula :

memory_used = MemTotal - ( MemFree + Active + Inactive + KReclaimable )

sar considers that:

memory_used = MemTotal - ( Memfree + Buffers + Cached + Slab )

Memfree + Buffers + cached + Slab seems reported constant (which is not surprising since Linux tends to cache as much as possible), we could suspect high variations in Memfree (compensated by Cached) and or in Active, Inactive, Kreclaimable values.

Going further would require much more informations about the configuration of your system and the applications running around 8, 10 and 12.

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  • great answer, thank you so much! Just one more question, where did you find what is the equation that sar uses for memory_used? Commented May 7, 2024 at 16:38
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    @VaTo : As part of the sar man page I linked to :(see details of the -r option, kbmemused sub paragraph) ;-) Commented May 7, 2024 at 18:41
  • Amazing! Thank you very much! Commented May 7, 2024 at 18:48

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