docs: update information about tsdb usage in cluster version (#4678)

update information about tsdb usage in cluster version

docs/README.md

@@ -404,6 +404,11 @@ matching the specified [series selector](https://prometheus.io/docs/prometheus/l
 
 Cardinality explorer is built on top of [/api/v1/status/tsdb](#tsdb-stats).
 
+In [cluster version of VictoriaMetrics](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html) each vmstorage tracks the stored time series individually.
+vmselect requests stats via [/api/v1/status/tsdb](#tsdb-stats) API from each vmstorage node and merges the results by summing per-series stats.
+This may lead to inflated values when samples for the same time series are spread across multiple vmstorage nodes
+due to [replication](#replication) or [rerouting](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html?highlight=re-routes#cluster-availability).
+
 See [cardinality explorer playground](https://play.victoriametrics.com/select/accounting/1/6a716b0f-38bc-4856-90ce-448fd713e3fe/prometheus/graph/#/cardinality).
 See the example of using the cardinality explorer [here](https://victoriametrics.com/blog/cardinality-explorer/).
 
@@ -1787,6 +1792,11 @@ VictoriaMetrics returns TSDB stats at `/api/v1/status/tsdb` page in the way simi
 * `match[]=SELECTOR` where `SELECTOR` is an arbitrary [time series selector](https://prometheus.io/docs/prometheus/latest/querying/basics/#time-series-selectors) for series to take into account during stats calculation. By default all the series are taken into account.
 * `extra_label=LABEL=VALUE`. See [these docs](#prometheus-querying-api-enhancements) for more details.
 
+In [cluster version of VictoriaMetrics](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html) each vmstorage tracks the stored time series individually.
+vmselect requests stats via [/api/v1/status/tsdb](#tsdb-stats) API from each vmstorage node and merges the results by summing per-series stats.
+This may lead to inflated values when samples for the same time series are spread across multiple vmstorage nodes
+due to [replication](#replication) or [rerouting](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html?highlight=re-routes#cluster-availability).
+
 VictoriaMetrics provides an UI on top of `/api/v1/status/tsdb` - see [cardinality explorer docs](#cardinality-explorer).
 
 ## Query tracing

docs/Single-server-VictoriaMetrics.md

@@ -412,6 +412,11 @@ matching the specified [series selector](https://prometheus.io/docs/prometheus/l
 
 Cardinality explorer is built on top of [/api/v1/status/tsdb](#tsdb-stats).
 
+In [cluster version of VictoriaMetrics](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html) each vmstorage tracks the stored time series individually.
+vmselect requests stats via [/api/v1/status/tsdb](#tsdb-stats) API from each vmstorage node and merges the results by summing per-series stats.
+This may lead to inflated values when samples for the same time series are spread across multiple vmstorage nodes
+due to [replication](#replication) or [rerouting](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html?highlight=re-routes#cluster-availability).
+
 See [cardinality explorer playground](https://play.victoriametrics.com/select/accounting/1/6a716b0f-38bc-4856-90ce-448fd713e3fe/prometheus/graph/#/cardinality).
 See the example of using the cardinality explorer [here](https://victoriametrics.com/blog/cardinality-explorer/).
 
@@ -1795,6 +1800,11 @@ VictoriaMetrics returns TSDB stats at `/api/v1/status/tsdb` page in the way simi
 * `match[]=SELECTOR` where `SELECTOR` is an arbitrary [time series selector](https://prometheus.io/docs/prometheus/latest/querying/basics/#time-series-selectors) for series to take into account during stats calculation. By default all the series are taken into account.
 * `extra_label=LABEL=VALUE`. See [these docs](#prometheus-querying-api-enhancements) for more details.
 
+In [cluster version of VictoriaMetrics](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html) each vmstorage tracks the stored time series individually.
+vmselect requests stats via [/api/v1/status/tsdb](#tsdb-stats) API from each vmstorage node and merges the results by summing per-series stats.
+This may lead to inflated values when samples for the same time series are spread across multiple vmstorage nodes
+due to [replication](#replication) or [rerouting](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html?highlight=re-routes#cluster-availability).
+
 VictoriaMetrics provides an UI on top of `/api/v1/status/tsdb` - see [cardinality explorer docs](#cardinality-explorer).
 
 ## Query tracing