br: add more info about the br log structure (#20443) (#20458)

Author: ti-chi-bot

br/br-log-architecture.md

@@ -108,18 +108,24 @@ Log backup generates the following types of files:
 .
 ├── v1
 │   ├── backupmeta
-│   │   ├── {min_restored_ts}-{uuid}.meta
-│   │   ├── {checkpoint}-{uuid}.meta
+│   │   ├── ...
+│   │   └── {resolved_ts}-{uuid}.meta
 │   ├── global_checkpoint
-│   │   ├── {store_id}.ts
-│   ├── {date}
-│   │   ├── {hour}
-│   │   │   ├── {store_id}
-│   │   │   │   ├── {min_ts}-{uuid}.log
-│   │   │   │   ├── {min_ts}-{uuid}.log
-├── v1_stream_truncate_safepoint.txt
+│   │   └── {store_id}.ts
+│   └── {date}
+│       └── {hour}
+│           └── {store_id}
+│               ├── ...
+│               └── {min_ts}-{uuid}.log
+└── v1_stream_truncate_safepoint.txt
 ```
 
+Explanation of the backup file directory structure:
+
+- `backupmeta`: stores backup metadata. The `resolved_ts` in the filename indicates the backup progress, meaning that data before this TSO has been fully backed up. However, note that this TSO only reflects the progress of certain shards.
+- `global_checkpoint`: represents the global backup progress. It records the latest point in time to which data can be restored using `br restore point`.
+- `{date}/{hour}`: stores backup data for the corresponding date and hour. When cleaning up storage, always use `br log truncate` instead of manually deleting data. This is because the metadata references the data in this directory, and manual deletion might lead to restore failures or data inconsistencies after restore.
+
 The following is an example:
 
 ```
@@ -129,24 +135,24 @@ The following is an example:
 │   │   ├── ...
 │   │   ├── 435213818858112001-e2569bda-a75a-4411-88de-f469b49d6256.meta
 │   │   ├── 435214043785779202-1780f291-3b8a-455e-a31d-8a1302c43ead.meta
-│   │   ├── 435214443785779202-224f1408-fff5-445f-8e41-ca4fcfbd2a67.meta
+│   │   └── 435214443785779202-224f1408-fff5-445f-8e41-ca4fcfbd2a67.meta
 │   ├── global_checkpoint
 │   │   ├── 1.ts
 │   │   ├── 2.ts
-│   │   ├── 3.ts
-│   ├── 20220811
-│   │   ├── 03
-│   │   │   ├── 1
-│   │   │   │   ├── ...
-│   │   │   │   ├── 435213866703257604-60fcbdb6-8f55-4098-b3e7-2ce604dafe54.log
-│   │   │   │   ├── 435214023989657606-72ce65ff-1fa8-4705-9fd9-cb4a1e803a56.log
-│   │   │   ├── 2
-│   │   │   │   ├── ...
-│   │   │   │   ├── 435214102632857605-11deba64-beff-4414-bc9c-7a161b6fb22c.log
-│   │   │   │   ├── 435214417205657604-e6980303-cbaa-4629-a863-1e745d7b8aed.log
-│   │   │   ├── 3
-│   │   │   │   ├── ...
-│   │   │   │   ├── 435214495848857605-7bf65e92-8c43-427e-b81e-f0050bd40be0.log
-│   │   │   │   ├── 435214574492057604-80d3b15e-3d9f-4b0c-b133-87ed3f6b2697.log
-├── v1_stream_truncate_safepoint.txt
+│   │   └── 3.ts
+│   └── 20220811
+│       └── 03
+│           ├── 1
+│           │   ├── ...
+│           │   ├── 435213866703257604-60fcbdb6-8f55-4098-b3e7-2ce604dafe54.log
+│           │   └── 435214023989657606-72ce65ff-1fa8-4705-9fd9-cb4a1e803a56.log
+│           ├── 2
+│           │   ├── ...
+│           │   ├── 435214102632857605-11deba64-beff-4414-bc9c-7a161b6fb22c.log
+│           │   └── 435214417205657604-e6980303-cbaa-4629-a863-1e745d7b8aed.log
+│           └── 3
+│               ├── ...
+│               ├── 435214495848857605-7bf65e92-8c43-427e-b81e-f0050bd40be0.log
+│               └── 435214574492057604-80d3b15e-3d9f-4b0c-b133-87ed3f6b2697.log
+└── v1_stream_truncate_safepoint.txt
 ```