Add information of hashAgg for memory control

configure-memory-usage.md

@@ -118,3 +118,84 @@ The following example constructs a memory-intensive SQL statement that triggers
     * `record path` indicates the directory of status files.
 
 5. You can see a set of files in the directory of status files (In the above example, the directory is `/tmp/1000_tidb/MC4wLjAuMDo0MDAwLzAuMC4wLjA6MTAwODA=/tmp-storage/record`), including `goroutinue`, `heap`, and `running_sql`. These three files are suffixed with the time when status files are logged. They respectively record goroutine stack information, the usage status of heap memory, and the running SQL information when the alarm is triggered. For the format of log content in `running_sql`, refer to [`expensive-queries`](/identify-expensive-queries.md).
+
+## Other memory control behaviors of tidb-server
+
+### Flow control
+
+- TiDB supports dynamic memory control for the operator that reads data. By default, this operator uses the maximum number of threads that [`tidb_disql_scan_concurrency`](/system-variables.md#tidb_distsql_scan_concurrency) allows to read data. When the memory usage of a single SQL execution exceeds [`tidb_mem_quota_query`](/system-variables.md#tidb_mem_quota_query) each time, the operator that reads data stops one thread.
+
+- This flow control behavior is controlled by the system variable [`tidb_enable_rate_limit_action`](/system-variables.md#tidb_enable_rate_limit_action).
+- When the flow control behavior is triggered, TiDB outputs a log containing the keywords `memory exceeds quota, destroy one token now`.
+
+### Disk spill
+
+TiDB supports disk spill for execution operators. When the memory usage of a SQL execution exceeds the memory quota, tidb-server can spill the intermediate data of execution operators to the disk to relieve memory pressure. Operators supporting disk spill include Sort, MergeJoin, HashJoin, and HashAgg.
+
+- The disk spill behavior is jointly controlled by the [`mem-quota-query`](/tidb-configuration-file.md#mem-quota-query), [`oom-use-tmp-storage`](/tidb-configuration-file.md#oom-use-tmp-storage), [`tmp-storage-path`](/tidb-configuration-file.md#tmp-storage-path), and [`tmp-storage-quota`](/tidb-configuration-file.md#tmp-storage-quota) parameters.
+- When the disk spill is triggered, TiDB outputs a log containing the keywords `memory exceeds quota, spill to disk now` or `memory exceeds quota, set aggregate mode to spill-mode`.
+- Disk spill for the Sort, MergeJoin, and HashJoin operator is introduced in v4.0.0; disk spill for the HashAgg operator is introduced in v5.2.0.
+- When the SQL executions containing Sort, MergeJoin, or HashJoin cause OOM, TiDB triggers disk spill by default. When SQL executions containing HashAgg cause OOM, TiDB does not trigger disk spill by default. You can configure the system variable `tidb_executor_concurrency = 1` to trigger disk spill for HashAgg.
+
+> **Note:**
+>
+> The disk spill for HashAgg does not support SQL executions containing the `DISTINCT` aggregate function. When a SQL execution containing a `DISTINCT` aggregate function uses too much memory, the disk spill does not apply.
+
+The following example uses a memory-consuming SQL statement to demonstrate the disk spill feature for HashAgg:
+
+1. Configure the memory quota of a SQL statement to 1GB (1 GB by default):
+
+    {{< copyable "sql" >}}
+
+    ```sql
+    set tidb_mem_quota_query = 1 << 30;
+    ```
+
+2. Create a single table `CREATE TABLE t(a int);` and insert 256 rows of different data.
+
+3. Execute the following SQL statement:
+
+    {{< copyable "sql" >}}
+
+    ```sql
+    [tidb]> explain analyze select /*+ HASH_AGG() */ count(*) from t t1 join t t2 join t t3 group by t1.a, t2.a, t3.a;
+    ```
+
+    Because executing this SQL statement occupies too much memory, the following "Out of Memory Quota" error message is returned:
+
+    ```sql
+    ERROR 1105 (HY000): Out Of Memory Quota![conn_id=3]
+    ```
+
+4. Configure the system variable `tidb_executor_concurrency` to 1. With this configuration, when out of memory, HashAgg automatically tries to trigger disk spill.
+
+    {{< copyable "sql" >}}
+
+    ```sql
+    set tidb_executor_concurrency = 1;
+    ```
+
+5. Execute the same SQL statement. You can find that this time, the statement is successfully executed and no error message is returned. From the following detailed execution plan, you can see that HashAgg has used 600 MB of hard disk space.
+
+    {{< copyable "sql" >}}
+
+    ```sql
+    [tidb]> explain analyze select /*+ HASH_AGG() */ count(*) from t t1 join t t2 join t t3 group by t1.a, t2.a, t3.a;
+    ```
+
+    ```sql
+    +---------------------------------+-------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------+-----------+----------+
+    | id                              | estRows     | actRows  | task      | access object | execution info                                                                                                                                                      | operator info                                                   | memory    | disk     |
+    +---------------------------------+-------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------+-----------+----------+
+    | HashAgg_11                      | 204.80      | 16777216 | root      |               | time:1m37.4s, loops:16385                                                                                                                                           | group by:test.t.a, test.t.a, test.t.a, funcs:count(1)->Column#7 | 1.13 GB   | 600.0 MB |
+    | └─HashJoin_12                   | 16777216.00 | 16777216 | root      |               | time:21.5s, loops:16385, build_hash_table:{total:267.2µs, fetch:228.9µs, build:38.2µs}, probe:{concurrency:1, total:35s, max:35s, probe:35s, fetch:962.2µs}         | CARTESIAN inner join                                            | 8.23 KB   | 4 KB     |
+    |   ├─TableReader_21(Build)       | 256.00      | 256      | root      |               | time:87.2µs, loops:2, cop_task: {num: 1, max: 150µs, proc_keys: 0, rpc_num: 1, rpc_time: 145.1µs, copr_cache_hit_ratio: 0.00}                                       | data:TableFullScan_20                                           | 885 Bytes | N/A      |
+    |   │ └─TableFullScan_20          | 256.00      | 256      | cop[tikv] | table:t3      | tikv_task:{time:23.2µs, loops:256}                                                                                                                                  | keep order:false, stats:pseudo                                  | N/A       | N/A      |
+    |   └─HashJoin_14(Probe)          | 65536.00    | 65536    | root      |               | time:728.1µs, loops:65, build_hash_table:{total:307.5µs, fetch:277.6µs, build:29.9µs}, probe:{concurrency:1, total:34.3s, max:34.3s, probe:34.3s, fetch:278µs}      | CARTESIAN inner join                                            | 8.23 KB   | 4 KB     |
+    |     ├─TableReader_19(Build)     | 256.00      | 256      | root      |               | time:126.2µs, loops:2, cop_task: {num: 1, max: 308.4µs, proc_keys: 0, rpc_num: 1, rpc_time: 295.3µs, copr_cache_hit_ratio: 0.00}                                    | data:TableFullScan_18                                           | 885 Bytes | N/A      |
+    |     │ └─TableFullScan_18        | 256.00      | 256      | cop[tikv] | table:t2      | tikv_task:{time:79.2µs, loops:256}                                                                                                                                  | keep order:false, stats:pseudo                                  | N/A       | N/A      |
+    |     └─TableReader_17(Probe)     | 256.00      | 256      | root      |               | time:211.1µs, loops:2, cop_task: {num: 1, max: 295.5µs, proc_keys: 0, rpc_num: 1, rpc_time: 279.7µs, copr_cache_hit_ratio: 0.00}                                    | data:TableFullScan_16                                           | 885 Bytes | N/A      |
+    |       └─TableFullScan_16        | 256.00      | 256      | cop[tikv] | table:t1      | tikv_task:{time:71.4µs, loops:256}                                                                                                                                  | keep order:false, stats:pseudo                                  | N/A       | N/A      |
+    +---------------------------------+-------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------+-----------+----------+
+    9 rows in set (1 min 37.428 sec)
+    ```

troubleshoot-write-conflicts.md

@@ -46,7 +46,7 @@ In the TiDB Grafana panel, check the following monitoring metrics under **KV Err
 
      ![kv-retry-duration](/media/troubleshooting-write-conflict-kv-retry-duration.png)
 
-You can also use `[kv:9007]Write conflict` as the key word to search in the TiDB log. The key word also indicates the write conflict exists in the cluster.
+You can also use `[kv:9007]Write conflict` as the keywords to search in the TiDB log. The keywords also indicate the write conflict exists in the cluster.
 
 ## Resolve write conflicts