docs: document events and slow query table reconciliation

docs/reference/sql/greptime-private/events.md

@@ -11,9 +11,14 @@ with Metasrv can additionally record operational event types. Event recording is
 asynchronous and best-effort, so rows are not an acknowledgement that an
 operation succeeded.
 
-The table is created when the first event is recorded. If no event has been
-recorded, or event recording is disabled, querying it returns a table-not-found
-error. Configure recording in [Event recording](/user-guide/deployments-administration/configuration.md#event-recording).
+When the event recorder writes its first event, it creates the
+`greptime_private.events` system table. If an existing table is missing columns
+from the current event schema, the recorder adds them. It performs both actions
+even when automatic table creation is disabled. Disabling event recording does
+not remove an existing table. A query returns a table-not-found error only if the
+table does not currently exist, for example because event recording was disabled
+before any event was recorded or the table was dropped. The recorder recreates the
+table when it writes another event. Configure recording in [Event recording](/user-guide/deployments-administration/configuration.md#event-recording).
 
 ```sql
 USE greptime_private;

docs/reference/sql/greptime-private/slow_queries.md

@@ -6,6 +6,9 @@ description: The slow queries table in the `greptime_private` database.
 # slow_queries
 
 The `slow_queries` table records SQL and PromQL queries selected by the slow-query recorder.
+When the slow-query recorder writes to `greptime_private.slow_queries`, it creates
+the table if it does not exist and adds any missing columns to an existing table.
+It performs both actions even when automatic table creation is disabled.
 
 :::tip NOTE
 The `slow_queries` table requires slow query logging to be enabled. See [Slow Query](/user-guide/deployments-administration/monitoring/slow-query.md) for configuration details.

docs/user-guide/deployments-administration/monitoring/events/overview.md

@@ -18,9 +18,14 @@ See [Event recording](/user-guide/deployments-administration/configuration.md#ev
 
 ## Query events
 
-The table is created when the first event is recorded. If no event has been
-recorded yet, or event recording is disabled, this query returns a table-not-found
-error.
+When the event recorder writes its first event, it creates the
+`greptime_private.events` system table. If an existing table is missing columns
+from the current event schema, the recorder adds them. It performs both actions
+even when automatic table creation is disabled. Disabling event recording does
+not remove an existing table. This query returns a table-not-found error only if
+the table does not currently exist, for example because event recording was
+disabled before any event was recorded or the table was dropped. The recorder
+recreates the table when it writes another event.
 
 Start with a bounded query while investigating a recent operation:
 

i18n/zh/docusaurus-plugin-content-docs/current/reference/sql/greptime-private/events.md

@@ -7,7 +7,7 @@ description: greptime_private 数据库中的 events 表。
 
 `events` 表保存 GreptimeDB 运行期间产生的事件。单机部署记录受支持的本地 DDL Procedure 事件；带有 Metasrv 的分布式部署还可以记录运维事件。事件会异步写入，写入失败不会影响原操作的执行结果。因此，不能以事件是否出现作为操作成功的依据。
 
-该表会在首次记录事件时自动创建。如果还没有事件记录，或已禁用事件记录，查询会提示表不存在。配置方法请参阅[事件记录配置](/user-guide/deployments-administration/configuration.md#事件记录配置)。
+事件记录器首次写入事件时会创建 `greptime_private.events` 系统表。如果现有表缺少当前事件表结构中的列，记录器会补齐这些列。即使自动建表已禁用，仍会执行这两项操作。禁用事件记录不会删除已有表。只有该表当前不存在时，查询才会提示表不存在，例如从启动时就禁用了事件记录，或者表已被删除。事件记录器在下一次写入事件时会重新创建该表。配置方法请参阅[事件记录配置](/user-guide/deployments-administration/configuration.md#事件记录配置)。
 
 ```sql
 USE greptime_private;

i18n/zh/docusaurus-plugin-content-docs/current/reference/sql/greptime-private/slow_queries.md

@@ -6,6 +6,7 @@ description: greptime_private 数据库中的慢查询表。
 # slow_queries
 
 `slow_queries` 表记录被慢查询记录器选中的 SQL 和 PromQL 查询。
+慢查询记录器写入 `greptime_private.slow_queries` 时，如果表不存在会创建表；如果现有表缺少列，则会补齐这些列。即使自动建表已禁用，仍会执行这两项操作。
 
 :::tip 注意
 `slow_queries` 表需要开启慢查询日志功能。详见[慢查询](/user-guide/deployments-administration/monitoring/slow-query.md)配置说明。

i18n/zh/docusaurus-plugin-content-docs/current/user-guide/deployments-administration/monitoring/events/overview.md

@@ -15,7 +15,7 @@ GreptimeDB 会异步写入事件记录，通常每 5 秒刷新一次。刚完成
 
 ## 查询事件
 
-事件表会在首次记录事件时创建。尚未记录任何事件，或已禁用事件记录时，下面的查询会报表不存在。
+事件记录器首次写入事件时会创建 `greptime_private.events` 系统表。如果现有表缺少当前事件表结构中的列，记录器会补齐这些列。即使自动建表已禁用，仍会执行这两项操作。禁用事件记录不会删除已有表。只有该表当前不存在时，下面的查询才会报表不存在，例如从启动时就禁用了事件记录，或者表已被删除。事件记录器在下一次写入事件时会重新创建该表。
 
 排查最近的操作时，可以先查询最近一小时的事件，并将结果限制为 20 条：