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[DOCS] Improve description of WAL record format (#14936) 

Signed-off-by: DC <413331538@qq.com>
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DC 2024-11-26 19:48:17 +08:00 committed by GitHub
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tsdb/docs/format/wal.md
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@ -17,7 +17,15 @@ Notable deviations are that the record fragment is encoded as:
└───────────┴──────────┴────────────┴──────────────┘
```
The type flag has the following states:
The initial type byte is made up of three components: a 3-bit reserved field, a 1-bit zstd compression flag, a 1-bit snappy compression flag, and a 3-bit type flag.
```
┌─────────────────┬──────────────────┬────────────────────┬──────────────────┐
│ reserved <3bit> │ zstd_flag <1bit> │ snappy_flag <1bit> │ type_flag <3bit> │
└─────────────────┴──────────────────┴────────────────────┴──────────────────┘
```
The lowest 3 bits within this flag represent the record type as follows:
* `0`: rest of page will be empty
* `1`: a full record encoded in a single fragment