TiFlash configuration: update io_rate_limit

tiflash/tiflash-configuration.md

@@ -67,13 +67,9 @@ delta_index_cache_size = 0
 
 ## Storage paths settings take effect starting from v4.0.9
 [storage]
-    ## [Experimental] New in v5.0. This item limits the total write rate of background tasks in bytes per second. It is not recommended to use this experimental feature in a production environment.
-    ## The unit is bytes. Currently, the setting such as "10GB" is not supported.
-    ## The default value is 0, which means no limit.
-    ## This parameter is used to control the usage of machine disk bandwidth by background tasks mainly for the scenario where TiFlash is deployed on the AWS EBS (gp2/gp3) disk.
-    ## This parameter can be used to improve the stability of the TiFlash query performance. The recommended configuration in this scenario is 50% of the disk bandwidth.
-    ## It is not recommended to modify this configuration in other scenarios.
-    bg_task_io_rate_limit = 0
+    ## This configuration item is deprecated since v5.2.0. You can use the `[storage.io_rate_limit]` settings below instead.
+
+    # bg_task_io_rate_limit = 0
 
     [storage.main]
     ## The list of directories to store the main data. More than 90% of the total data is stored in
@@ -100,6 +96,30 @@ delta_index_cache_size = 0
     ## If it is not set, or is set to multiple 0, the actual disk (the disk where the directory is located) capacity is used.
     # capacity = [ 10737418240, 10737418240 ]
 
+    ## [storage.io_rate_limit] settings are new in v5.2.0.
+    [storage.io_rate_limit]
+    ## This configuration item determines whether to limit the I/O traffic, which is disabled by default. This traffic limit in TiFlash is suitable for cloud storage that has disk bandwidth of a small and specific size.
+    ## The total I/O bandwidth for disk reads and writes. The unit is bytes and the default value is 0, which means the I/O traffic is not limited by default.
+    # max_bytes_per_sec = 0
+    ## `max_read_bytes_per_sec` and `max_write_bytes_per_sec` have similar meanings to `max_bytes_per_sec`. `max_read_bytes_per_sec` refers the total I/O bandwidth for disk reads, and `max_write_bytes_per_sec` means the total I/O bandwidth for disk writes.
+    ## These configuration items limit I/O bandwidth for disk reads and writes separately. You can use them for cloud storage that calculates the limit of I/O bandwidth for disk reads and writes separately, such as the Persistent Disk provided by Google Cloud Platform.
+    ## When the value of `max_bytes_per_sec` is not `0`, `max_bytes_per_sec` is prioritized.
+    # max_read_bytes_per_sec = 0
+    # max_write_bytes_per_sec = 0
+
+    ## The following parameters control the bandwidth weights assigned to different I/O traffic types. Generally, you do not need to adjust these parameters.
+    ## TiFlash internally divides I/O requests into four types: foreground writes, background writes, foreground reads, background reads.
+    ## When the I/O traffic limit is initialized, TiFlash assigns the bandwidth according to the following weight ratio.
+    ## The following  default configurations indicate that each type of traffic gets a weight of 25% (25 / (25 + 25 + 25 + 25) = 25%).
+    ## If the weight is configured to `0`, the corresponding I/O traffic is not limited.
+    # foreground_write_weight = 25
+    # background_write_weight = 25
+    # foreground_read_weight = 25
+    # background_read_weight = 25
+    ## TiFlash supports automatically tuning the traffic limit for different I/O types according to the current I/O load. Sometimes, the tuned bandwidth might exceed the weight ratio set above.
+    ## `auto_tune_sec` indicates the interval of automatic tuning. The unit is seconds. If the value of `auto_tune_sec` is `0`, the automatic tuning is disabled.
+    # auto_tune_sec = 5
+
 [flash]
     tidb_status_addr = TiDB status port and address. # Multiple addresses are separated with commas.
     service_addr = The listening address of TiFlash Raft services and coprocessor services.