tiflash: Add warnings about LOCATION LABELS on ALTER TABLE ... SET TIFLASH REPLICA

tiflash/create-tiflash-replicas.md

@@ -233,47 +233,50 @@ When configuring replicas, if you need to distribute TiFlash replicas to multipl
 
     Note that the `flash.proxy.labels` configuration in earlier versions cannot handle special characters in the available zone name correctly. It is recommended to use the `server.labels` in `learner_config` to configure the name of an available zone.
 
-2. After starting a cluster, specify the labels when creating replicas.
+2. After starting a cluster, specify the number of TiFlash replicas for high availability. The syntax is as follows:
 
     ```sql
-    ALTER TABLE table_name SET TIFLASH REPLICA count LOCATION LABELS location_labels;
+    ALTER TABLE table_name SET TIFLASH REPLICA count;
     ```
 
     For example:
 
     ```sql
-    ALTER TABLE t SET TIFLASH REPLICA 2 LOCATION LABELS "zone";
+    ALTER TABLE t SET TIFLASH REPLICA 2;
     ```
 
-3. PD schedules the replicas based on the labels. In this example, PD respectively schedules two replicas of the table `t` to two available zones. You can use pd-ctl to view the scheduling.
+3. PD schedules the replicas of the table `t` to different availability zones based on the `server.labels` in the TiFlash node's `learner_config` and the number (`count`) of the table's replicas, ensuring availability. For more information, see [Schedule Replicas by Topology Labels](https://docs.pingcap.com/tidb/stable/schedule-replicas-by-topology-labels/). You can use the following SQL statement to verify the distribution of a table's Regions across TiFlash nodes:
 
-    ```shell
-    > tiup ctl:v<CLUSTER_VERSION> pd -u http://<PD_ADDRESS>:2379 store
-
-        ...
-        "address": "172.16.5.82:23913",
-        "labels": [
-          { "key": "engine", "value": "tiflash"},
-          { "key": "zone", "value": "z1" }
-        ],
-        "region_count": 4,
-
-        ...
-        "address": "172.16.5.81:23913",
-        "labels": [
-          { "key": "engine", "value": "tiflash"},
-          { "key": "zone", "value": "z1" }
-        ],
-        "region_count": 5,
-        ...
-
-        "address": "172.16.5.85:23913",
-        "labels": [
-          { "key": "engine", "value": "tiflash"},
-          { "key": "zone", "value": "z2" }
-        ],
-        "region_count": 9,
-        ...
+    ```sql
+    -- Non-partitioned table
+    SELECT table_id, p.store_id, address, COUNT(p.region_id) 
+    FROM
+      information_schema.tikv_region_status r,
+      information_schema.tikv_region_peers p,
+      information_schema.tikv_store_status s
+    WHERE
+      r.db_name = 'test' 
+      AND r.table_name = 'table_to_check'
+      AND r.region_id = p.region_id 
+      AND p.store_id = s.store_id
+      AND JSON_EXTRACT(s.label, '$[0].value') = 'tiflash'
+    GROUP BY table_id, p.store_id, address;
+
+    -- Partitioned table
+    SELECT table_id, r.partition_name, p.store_id, address, COUNT(p.region_id)
+    FROM
+      information_schema.tikv_region_status r,
+      information_schema.tikv_region_peers p,
+      information_schema.tikv_store_status s
+    WHERE 
+      r.db_name = 'test' 
+      AND r.table_name = 'table_to_check' 
+      AND r.partition_name LIKE 'p202312%'
+      AND r.region_id = p.region_id 
+      AND p.store_id = s.store_id
+      AND JSON_EXTRACT(s.label, '$[0].value') = 'tiflash'
+    GROUP BY table_id, r.partition_name, p.store_id, address
+    ORDER BY table_id, r.partition_name, p.store_id;
     ```
 
 <CustomContent platform="tidb">
@@ -283,3 +286,7 @@ For more information about scheduling replicas by using labels, see [Schedule Re
 TiFlash supports configuring the replica selection strategy for different zones. For more information, see [`tiflash_replica_read`](/system-variables.md#tiflash_replica_read-new-in-v730).
 
 </CustomContent>
+
+> **Note:**
+>
+> In the syntax `ALTER TABLE table_name SET TIFLASH REPLICA count LOCATION LABELS location_labels;`, if you specify multiple labels for `location_labels`, TiDB cannot parse them correctly to set placement rules. Therefore, do not use `LOCATION LABELS` to configure TiFlash replicas.