oleg-vlsk commented on code in PR #13204:
URL: https://github.com/apache/ignite/pull/13204#discussion_r3471373418
##########
docs/_docs/memory-configuration/eviction-policies.adoc:
##########
@@ -48,6 +48,24 @@ If you don't use data regions, you have to explicitly add
default data region pa
By default, eviction starts when the overall RAM consumption by a region gets
to 90%.
Use the `DataRegionConfiguration.setEvictionThreshold(...)` parameter if you
need to initiate eviction earlier or later.
+=== Monitoring Page Eviction
+
+When page eviction starts due to a data region being under memory pressure,
Ignite sets the `EvictionsStarted` metric to `true` for that data region.
+This metric is relevant for in-memory data regions, where page eviction can
remove data from memory and the data must be reloaded later.
+It is available in the `io.dataregion.{data_region_name}` registry.
+After `EvictionsStarted` becomes `true`, it remains `true` until the node is
restarted.
+Use it together with `EvictionRate` to monitor whether eviction has started
and how actively pages are being evicted.
+
+Ignite also logs a warning when page-based eviction starts:
+
+[source,text]
+----
+Page-based evictions started. Consider increasing 'maxSize' on Data Region
configuration: <region_name>
+----
+
+The warning is logged once per data region.
+For monitoring, prefer the `EvictionsStarted` metric because it identifies the
affected data region directly and does not depend on log parsing.
Review Comment:
After IGNITE-28099 current log message also contains the affected data
region name. So I would not use that as the main distinction between metric and
log-based monitoring. The stronger point is that as a metric EvictionsStarted
can be used directly used by monitoring tools without relying on log parsing.
##########
docs/_docs/memory-configuration/eviction-policies.adoc:
##########
@@ -48,6 +48,24 @@ If you don't use data regions, you have to explicitly add
default data region pa
By default, eviction starts when the overall RAM consumption by a region gets
to 90%.
Use the `DataRegionConfiguration.setEvictionThreshold(...)` parameter if you
need to initiate eviction earlier or later.
+=== Monitoring Page Eviction
+
+When page eviction starts due to a data region being under memory pressure,
Ignite sets the `EvictionsStarted` metric to `true` for that data region.
+This metric is relevant for in-memory data regions, where page eviction can
remove data from memory and the data must be reloaded later.
Review Comment:
I would not mention the fact that the data will have to be reloaded to the
cluster, that is not relevant for page eviction monitoring.
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