prometheus/tsdb/docs/format/chunks.md

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# Chunks Disk Format
The following describes the format of a chunks file,
which is created in the `chunks/` directory of a block.
The maximum size per segment file is 512MiB.
Chunks in the files are referenced from the index by uint64 composed of
in-file offset (lower 4 bytes) and segment sequence number (upper 4 bytes).
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```
┌──────────────────────────────┐
│ magic(0x85BD40DD) <4 byte>
├──────────────────────────────┤
│ version(1) <1 byte>
├──────────────────────────────┤
│ padding(0) <3 byte>
├──────────────────────────────┤
│ ┌──────────────────────────┐ │
│ │ Chunk 1 │ │
│ ├──────────────────────────┤ │
│ │ ... │ │
│ ├──────────────────────────┤ │
│ │ Chunk N │ │
│ └──────────────────────────┘ │
└──────────────────────────────┘
```
# Chunk
```
┌───────────────┬───────────────────┬──────────────┬────────────────┐
│ len <uvarint> │ encoding <1 byte> │ data <bytes> │ CRC32 <4 byte>
└───────────────┴───────────────────┴──────────────┴────────────────┘
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```