deployment/docker/rules: add VMSelectConcurrentQueriesExceedMemoryLimit alert

Warn users when cluster is misconfigured to allow too many concurrent selects

app/vmselect/promql/eval.go

@@ -1687,6 +1687,10 @@ func assertInstantValues(tss []*timeseries) {
 
 var memoryIntensiveQueries = metrics.NewCounter(`vm_memory_intensive_queries_total`)
 
+var _ = metrics.NewGauge(`vm_max_memory_per_query`, func() float64 {
+	return float64(maxMemoryPerQuery.N)
+})
+
 func evalRollupFuncWithMetricExpr(qt *querytracer.Tracer, ec *EvalConfig, funcName string, rf rollupFunc,
 	expr metricsql.Expr, me *metricsql.MetricExpr, iafc *incrementalAggrFuncContext, windowExpr *metricsql.DurationExpr,
 ) ([]*timeseries, error) {

deployment/docker/rules/alerts-cluster.yml

@@ -223,4 +223,16 @@ groups:
             Unexpected TSID misses for \"{{ $labels.job }}\" ({{ $labels.instance }}) for the last 15 minutes.
             If this happens after unclean shutdown of VictoriaMetrics process (via \"kill -9\", OOM or power off),
             then this is OK - the alert must go away in a few minutes after the restart.
-            Otherwise this may point to the corruption of index data.
+            Otherwise this may point to the corruption of index data.
+
+      - alert: VMSelectConcurrentQueriesExceedMemoryLimit
+        expr: (vm_max_memory_per_query * on(job, instance) vm_concurrent_select_capacity) > on(job, instance) vm_available_memory_bytes
+        for: 5m
+        labels:
+          severity: warning
+        annotations:
+          summary: "vmselect ({{ $labels.instance }}) concurrent query memory may exceed pod limit"
+          description: "Current concurrent queries ({{ $value | humanize1024 }} combined max memory) exceed
+            the available memory on instance {{ $labels.instance }}.
+            This may result in OOM kills. Consider reducing -maxConcurrentRequests,
+            lowering -maxMemoryPerQuery, or scaling up pod memory limits."

docs/victoriametrics/changelog/CHANGELOG.md

@@ -28,6 +28,8 @@ See also [LTS releases](https://docs.victoriametrics.com/victoriametrics/lts-rel
 
 * SECURITY: upgrade base docker image (Alpine) from 3.23.4 to 3.24.1. See [Alpine 3.24.1 release notes](https://www.alpinelinux.org/posts/Alpine-3.24.1-released.html).
 
+* FEATURE: `vmselect` in [VictoriaMetrics cluster](https://docs.victoriametrics.com/victoriametrics/cluster-victoriametrics/): expose `vm_max_memory_per_query` metric reflecting the `-search.maxMemoryPerQuery` limit. Create `VMSelectConcurrentQueriesExceedMemoryLimit` alert to warn when OOMs are possible due to misconfiguration of `-search.maxMemoryPerQuery` and max concurrent queries.
+
 * FEATURE: [vmauth](https://docs.victoriametrics.com/victoriametrics/vmauth/): add `default_vm_access_claim` field into `jwt` section of auth config. It could be used at [JWT claim placeholders](https://docs.victoriametrics.com/victoriametrics/vmauth/#jwt-claim-based-request-templating), if `JWT` token doesn't have `vm_access` claim. See [#11054](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/11054).
 * FEATURE: [vmagent](https://docs.victoriametrics.com/victoriametrics/vmagent/): reduces CPU usage by 10% at [sharding among remote storages](https://docs.victoriametrics.com/victoriametrics/vmagent/#sharding-among-remote-storages). See [#11113](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/11113). Thanks to @bennf for contribution.
 * FEATURE: [vmsingle](https://docs.victoriametrics.com/victoriametrics/single-server-victoriametrics/) and `vmselect` in [VictoriaMetrics cluster](https://docs.victoriametrics.com/victoriametrics/cluster-victoriametrics/): add `optimize_repeated_binary_op_subexprs=1` query arg to [/api/v1/query_range](https://docs.victoriametrics.com/victoriametrics/keyconcepts/#range-query) for executing binary operator sides sequentially when they share the same optimized aggregate rollup result expression. This allows the second side to reuse rollup result cache populated by the first side. See [#10575](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/10575).