Correct calc and explain how to get METRICS in RAM usage (#14733)
Correct calc and explain how to get METRICS
Chris Akritidis committed
Mar 15, 2023 at 07:19 UTC
2b01eb68bbfb338fa20fc5e948ea5e7fcb0799ba
1 file changed
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docs/store/change-metrics-storage.md
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@@ -92,7 +92,15 @@ The quick rule of thumb, for a high level estimation is
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DBENGINE memory in MiB = METRICS x (TIERS - 1) x 8 / 1024 MiB
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Total Netdata memory in MiB = Metric cardinality factor x DBENGINE memory in MiB + "dbengine page cache size MB" from netdata.conf
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```
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-The cardinality factor is usually between 3 or 4 and depends mainly on the ephemerality of the collected metrics. The more ephemeral
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+You can get the currently collected **METRICS** from the "dbengine metrics" chart of the Netdata dashboard. You just need to divide the
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+value of the "collected" dimension with the number of tiers. For example, at the specific point highlighted in the chart below, 608k metrics
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+were being collected across all 3 tiers, which means that `METRICS = 608k / 3 = 203667`.
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+<img width="988" alt="image" src="https://user-images.githubusercontent.com/43294513/225335899-a9216ba7-a09e-469e-89f6-4690aada69a4.png" />
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+The **cardinality factor** is usually between 3 or 4 and depends mainly on the ephemerality of the collected metrics. The more ephemeral
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the infrastructure, the higher the factor. If the cardinality is extremely high with a lot of extremely short lived containers
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(hundreds started every minute), the multiplication factor can get really high. In such cases, we recommend splitting the load across
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multiple Netdata parents, until we can provide a way to lower the cardinality by aggregating similar metrics.
@@ -104,8 +112,9 @@ For 2000 metrics (dimensions) in 3 storage tiers and the default cache size:
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```
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DBENGINE memory for 2k metrics = 2000 x (3 - 1) x 8 / 1024 MiB = 32 MiB
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dbengine page cache size MB = 32 MiB
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-Total Netdata memory in MiB = Between 2*32 + 32 = 96 MiB and 3*32 + 32 = 196 MiB, for low to average cardinality
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+Total Netdata memory in MiB = 3*32 + 32 = 128 MiB (low cardinality)
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```
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#### Large parent RAM usage
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The Netdata parent in our production infrastructure at the time of writing: