docs: add unit in wal_retention_period description

docs/en/12-taos-sql/22-meta.md

@@ -98,7 +98,7 @@ Provides information about user-created databases. Similar to SHOW DATABASES.
 | 21  |      cachesize       | INT           | Memory per vnode used for caching the newest data. It should be noted that `cachesize` is a TDengine keyword and needs to be escaped with ` when used as a column name.                                                           |
 | 22  |      wal_level       | INT           | WAL level. It should be noted that `wal_level` is a TDengine keyword and needs to be escaped with ` when used as a column name.                                                                                                   |
 | 23  |   wal_fsync_period   | INT           | Interval at which WAL is written to disk. It should be noted that `wal_fsync_period` is a TDengine keyword and needs to be escaped with ` when used as a column name.                                                             |
-| 24  | wal_retention_period | INT           | WAL retention period. It should be noted that `wal_retention_period` is a TDengine keyword and needs to be escaped with ` when used as a column name.                                                                             |
+| 24  | wal_retention_period | INT           | WAL retention period, in seconds. It should be noted that `wal_retention_period` is a TDengine keyword and needs to be escaped with ` when used as a column name.                                                                             |
 | 25  |  wal_retention_size  | INT           | Maximum WAL size. It should be noted that `wal_retention_size` is a TDengine keyword and needs to be escaped with ` when used as a column name.                                                                                   |
 | 26  |   wal_roll_period    | INT           | WAL rotation period. It should be noted that `wal_roll_period` is a TDengine keyword and needs to be escaped with ` when used as a column name.                                                                                   |
 | 27  |   wal_segment_size   | BIGINT        | WAL file size. It should be noted that `wal_segment_size` is a TDengine keyword and needs to be escaped with ` when used as a column name.                                                                                        |

docs/zh/12-taos-sql/22-meta.md

@@ -98,7 +98,7 @@ TDengine 内置了一个名为 `INFORMATION_SCHEMA` 的数据库，提供对数
 | 21  |      cachesize       | INT          | 表示每个 vnode 中用于缓存子表最近数据的内存大小。需要注意，`cachesize` 为 TDengine 关键字，作为列名使用时需要使用 ` 进行转义。                      |
 | 22  |      wal_level       | INT          | WAL 级别。需要注意，`wal_level` 为 TDengine 关键字，作为列名使用时需要使用 ` 进行转义。                                                             |
 | 23  |   wal_fsync_period   | INT          | 数据落盘周期。需要注意，`wal_fsync_period` 为 TDengine 关键字，作为列名使用时需要使用 ` 进行转义。                                                  |
-| 24  | wal_retention_period | INT          | WAL 的保存时长。需要注意，`wal_retention_period` 为 TDengine 关键字，作为列名使用时需要使用 ` 进行转义。                                            |
+| 24  | wal_retention_period | INT          | WAL 的保存时长，单位为秒。需要注意，`wal_retention_period` 为 TDengine 关键字，作为列名使用时需要使用 ` 进行转义。                                            |
 | 25  |  wal_retention_size  | INT          | WAL 的保存上限。需要注意，`wal_retention_size` 为 TDengine 关键字，作为列名使用时需要使用 ` 进行转义。                                              |
 | 26  |   wal_roll_period    | INT          | wal 文件切换时长。需要注意，`wal_roll_period` 为 TDengine 关键字，作为列名使用时需要使用 ` 进行转义。                                               |
 | 27  |   wal_segment_size   | BIGINT       | wal 单个文件大小。需要注意，`wal_segment_size` 为 TDengine 关键字，作为列名使用时需要使用 ` 进行转义。                                              |