Update tidb-resource-control.md

pingcap · Jul 3, 2023 · e578bb4 · e578bb4
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commit e578bb4
Showing 1 changed file with 39 additions and 14 deletions.
diff --git a/tidb-resource-control.md b/tidb-resource-control.md
@@ -43,21 +43,46 @@ Currently, the resource control feature has the following limitations:
 
 ## What is Request Unit (RU)
 
-Request Unit (RU) is a unified abstraction unit in TiDB for system resources, which currently includes CPU, IOPS, and IO bandwidth metrics. The consumption of these three metrics is represented by RU according to a certain ratio.
+Request Unit (RU) is a unified abstraction unit in TiDB for system resources, which currently includes CPU, IOPS, and IO bandwidth metrics. It is used to indicate the amount of resources consumed by a single request to the database. The number of RU's consumed by a request depends on a variety of factors, such as the type of operation or the amount of data being retrieved or modified. Currently, the RU contains statistics for the following resources:
+
+<table>
+    <thead>
+        <tr>
+            <th>Resource Type</th>
+            <th>RU Consumption</th>
+        </tr>
+    </thead>
+    <tbody>
+        <tr>
+            <td rowspan="3">Read</td>
+            <td>2 storage read batches consume 1 RU</td>
+        </tr>
+        <tr>
+            <td>8 storage read requests consume 1 RU</td>
+        </tr>
+            <td>64 KiB read request payload consumes 1 RU</td>
+        <tr>
+            <td rowspan="3">Write</td>
+            <td>1 storage write batch consumes 1 RU * (the number of replicas)</td>
+        </tr>
+        <tr>
+            <td>1 storage write request consumes 1 RU</td>
+        </tr>
+        <tr>
+            <td>1 KiB write request payload consumes 1 RU</td>
+        </tr>
+        <tr>
+            <td>SQL CPU</td>
+            <td> 3 ms consumes 1 RU</td>
+        </tr>
+    </tbody>
+</table>
 
-The following table shows the consumption of TiKV storage layer CPU and IO resources by user requests and the corresponding RU weights.
-
-| Resource        | RU Weight        |
-|:----------------|:-----------------|
-| CPU             | 1/3 RU per millisecond |
-| Read IO         | 1/64 RU per KB       |
-| Write IO        | 1 RU/KB          |
-| Basic overhead of a read request   | 0.25 RU  |
-| Basic overhead of a write request  | 1.5 RU   |
-
-Based on the above table, assuming that the TiKV time consumed by a resource group is `c` milliseconds, `r1` times of requests read `r2` KB data, `w1` times of write requests write `w2` KB data, and the number of non-witness TiKV nodes in the cluster is `n`. Then, the formula for the total RUs consumed by the resource group is as follows:
-
-`c`\* 1/3 + (`r1` \* 0.25 + `r2` \* 1/64) + (1.5 \* `w1` + `w2` \* 1 \* `n`)
+> **Note:**
+>
+> - Each write operation is eventually replicated to all replicas (by default TiKV has 3 replicas) and each replication operation is considered a different write operation.
+> - In addition to queries executed by the user, RU can be consumed by background tasks, such as automated statistical information collection.
+> - The preceding table lists only the resources involved in computing RUs for on-premises TiDB clusters, excluding the network and storage components. For TiDB Serverless RUs, see [TiDB Serverless Pricing Details](https://www.pingcap.com/tidb-cloud- serverless-pricing-details/).
 
 ## Parameters for resource control