diff --git a/docs/userguide/monitoring/promql-recipes.md b/docs/userguide/monitoring/promql-recipes.md
new file mode 100644
index 000000000..d96fe430e
--- /dev/null
+++ b/docs/userguide/monitoring/promql-recipes.md
@@ -0,0 +1,54 @@
+---
+title: Querying and joining metrics
+sidebar_label: PromQL recipes
+---
+
+HAMi exposes two complementary metrics endpoints: the scheduler's [cluster device allocation](device-allocation) endpoint reports what has been _allocated_, and the [real-time device usage](real-time-device-usage) endpoint reports what is actually being _used_. This page shows how to correlate the two views and lists a few ready-to-use PromQL queries.
+
+## Correlating the allocation and usage views
+
+Both endpoints label their per-device series with `device_uuid` (unique per physical GPU) and `zone`, so you can relate a device's allocation to its live usage in PromQL.
+
+The host usage metrics carry no `node` label — they are reported per device — while the scheduler metrics carry both `node` and `device_uuid`. To restrict host usage to a single node's devices, filter with `and on`:
+
+```promql
+hami_host_gpu_utilization_ratio
+  and on (device_uuid) hami_gpu_memory_limit_bytes{node="gpu-node-1"}
+```
+
+`and` returns the host series unchanged wherever a matching `device_uuid` exists on the right — it filters, but copies no labels. To actually attach the `node` label (for example, to group host usage by node), use a label-preserving arithmetic join instead:
+
+```promql
+hami_host_gpu_utilization_ratio
+  * on (device_uuid) group_left(node)
+  (hami_gpu_memory_limit_bytes * 0 + 1)
+```
+
+The right-hand `* 0 + 1` turns each scheduler series into `1`, so multiplying keeps the host value intact while `group_left(node)` carries the `node` label across.
+
+## Useful queries
+
+GPU memory allocated versus capacity per node, as a percentage:
+
+```promql
+100 * sum by (node) (hami_gpu_memory_allocated_bytes)
+    / sum by (node) (hami_gpu_memory_limit_bytes)
+```
+
+Containers using more than 80% of their vGPU memory limit:
+
+```promql
+100 * hami_vgpu_memory_used_bytes / (hami_vgpu_memory_limit_bytes > 0) > 80
+```
+
+Number of GPUs currently shared by more than one container:
+
+```promql
+count(hami_gpu_shared_count > 1)
+```
+
+:::note
+
+Ratio metrics (names ending in `_ratio`) are reported on a 0-100 (percent) scale, not the 0-1 scale some Prometheus conventions use. Keep that in mind when writing thresholds.
+
+:::
diff --git a/sidebars.js b/sidebars.js
index 3487c0e9f..2c8669f4d 100644
--- a/sidebars.js
+++ b/sidebars.js
@@ -83,6 +83,7 @@ module.exports = {
             "userguide/monitoring/real-time-usage",
             "userguide/monitoring/real-time-device-usage",
             "userguide/monitoring/grafana-dashboard",
+            "userguide/monitoring/promql-recipes",
           ],
         },
         {
diff --git a/versioned_docs/version-v2.9.0/userguide/monitoring/promql-recipes.md b/versioned_docs/version-v2.9.0/userguide/monitoring/promql-recipes.md
new file mode 100644
index 000000000..d96fe430e
--- /dev/null
+++ b/versioned_docs/version-v2.9.0/userguide/monitoring/promql-recipes.md
@@ -0,0 +1,54 @@
+---
+title: Querying and joining metrics
+sidebar_label: PromQL recipes
+---
+
+HAMi exposes two complementary metrics endpoints: the scheduler's [cluster device allocation](device-allocation) endpoint reports what has been _allocated_, and the [real-time device usage](real-time-device-usage) endpoint reports what is actually being _used_. This page shows how to correlate the two views and lists a few ready-to-use PromQL queries.
+
+## Correlating the allocation and usage views
+
+Both endpoints label their per-device series with `device_uuid` (unique per physical GPU) and `zone`, so you can relate a device's allocation to its live usage in PromQL.
+
+The host usage metrics carry no `node` label — they are reported per device — while the scheduler metrics carry both `node` and `device_uuid`. To restrict host usage to a single node's devices, filter with `and on`:
+
+```promql
+hami_host_gpu_utilization_ratio
+  and on (device_uuid) hami_gpu_memory_limit_bytes{node="gpu-node-1"}
+```
+
+`and` returns the host series unchanged wherever a matching `device_uuid` exists on the right — it filters, but copies no labels. To actually attach the `node` label (for example, to group host usage by node), use a label-preserving arithmetic join instead:
+
+```promql
+hami_host_gpu_utilization_ratio
+  * on (device_uuid) group_left(node)
+  (hami_gpu_memory_limit_bytes * 0 + 1)
+```
+
+The right-hand `* 0 + 1` turns each scheduler series into `1`, so multiplying keeps the host value intact while `group_left(node)` carries the `node` label across.
+
+## Useful queries
+
+GPU memory allocated versus capacity per node, as a percentage:
+
+```promql
+100 * sum by (node) (hami_gpu_memory_allocated_bytes)
+    / sum by (node) (hami_gpu_memory_limit_bytes)
+```
+
+Containers using more than 80% of their vGPU memory limit:
+
+```promql
+100 * hami_vgpu_memory_used_bytes / (hami_vgpu_memory_limit_bytes > 0) > 80
+```
+
+Number of GPUs currently shared by more than one container:
+
+```promql
+count(hami_gpu_shared_count > 1)
+```
+
+:::note
+
+Ratio metrics (names ending in `_ratio`) are reported on a 0-100 (percent) scale, not the 0-1 scale some Prometheus conventions use. Keep that in mind when writing thresholds.
+
+:::
diff --git a/versioned_sidebars/version-v2.9.0-sidebars.json b/versioned_sidebars/version-v2.9.0-sidebars.json
index 6d0cd8678..89ecd0747 100644
--- a/versioned_sidebars/version-v2.9.0-sidebars.json
+++ b/versioned_sidebars/version-v2.9.0-sidebars.json
@@ -86,7 +86,8 @@
             "userguide/monitoring/device-allocation",
             "userguide/monitoring/real-time-usage",
             "userguide/monitoring/real-time-device-usage",
-            "userguide/monitoring/grafana-dashboard"
+            "userguide/monitoring/grafana-dashboard",
+            "userguide/monitoring/promql-recipes"
           ]
         },
         {