oleg-vlsk commented on code in PR #13204:
URL: https://github.com/apache/ignite/pull/13204#discussion_r3434001326
##########
docs/_docs/memory-configuration/eviction-policies.adoc:
##########
@@ -48,6 +48,22 @@ 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 because a data region is under memory pressure,
Ignite sets the `EvictionsStarted` metric to `true` for that data region.
Review Comment:
“When page eviction starts because a data region is under memory
pressure...” sounds a bit unnatural. I would suggest rephrasing it as:
“When page eviction starts due to a data region being under memory
pressure...”
##########
docs/_docs/memory-configuration/eviction-policies.adoc:
##########
@@ -48,6 +48,22 @@ 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 because a data region is under memory pressure,
Ignite sets the `EvictionsStarted` metric to `true` for that data region.
+The metric is available in the `io.dataregion.{data_region_name}` registry.
+Use it together with `EvictionRate` to monitor whether eviction has started
and how actively pages are being evicted.
Review Comment:
It is probably worth mentioning that page eviction with potential data loss,
and therefore this metric, is relevant for in-memory clusters rather than
persistent ones.
##########
docs/_docs/memory-configuration/eviction-policies.adoc:
##########
@@ -48,6 +48,22 @@ 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 because a data region is under memory pressure,
Ignite sets the `EvictionsStarted` metric to `true` for that data region.
+The metric is available in the `io.dataregion.{data_region_name}` registry.
+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:
It would also be useful to mention that once eviction starts, the
EvictionsStarted metric remains set to `true` until the node is restarted.
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