statistics.md: correct the default value of stats-load-concurrency (pingcap#20460) (pingcap#20476)

Author: ti-chi-bot

statistics.md

@@ -478,7 +478,7 @@ To enable this feature, set the value of the [`tidb_stats_load_sync_wait`](/syst
 After enabling the synchronously loading statistics feature, you can further configure the feature as follows:
 
 - To control how TiDB behaves when the waiting time of SQL optimization reaches the timeout, modify the value of the [`tidb_stats_load_pseudo_timeout`](/system-variables.md#tidb_stats_load_pseudo_timeout-new-in-v540) system variable. The default value of this variable is `ON`, indicating that after the timeout, the SQL optimization process does not use any histogram, TopN, or CMSketch statistics on any columns. If this variable is set to `OFF`, after the timeout, SQL execution fails.
-- To specify the maximum number of columns that the synchronously loading statistics feature can process concurrently, modify the value of the [`stats-load-concurrency`](/tidb-configuration-file.md#stats-load-concurrency-new-in-v540) option in the TiDB configuration file. The default value is `5`.
+- To specify the maximum number of columns that the synchronously loading statistics feature can process concurrently, modify the value of the [`stats-load-concurrency`](/tidb-configuration-file.md#stats-load-concurrency-new-in-v540) option in the TiDB configuration file. Starting from v8.2.0, the default value of this option is `0`, indicating that TiDB automatically adjusts concurrency based on the server configuration.
 - To specify the maximum number of column requests that the synchronously loading statistics feature can cache, modify the value of the [`stats-load-queue-size`](/tidb-configuration-file.md#stats-load-queue-size-new-in-v540) option in the TiDB configuration file. The default value is `1000`.
 
 During TiDB startup, SQL statements executed before the initial statistics are fully loaded might have suboptimal execution plans, thus causing performance issues. To avoid such issues, TiDB v7.1.0 introduces the configuration parameter [`force-init-stats`](/tidb-configuration-file.md#force-init-stats-new-in-v657-and-v710). With this option, you can control whether TiDB provides services only after statistics initialization has been finished during startup. Starting from v7.2.0, this parameter is enabled by default.