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44 lines
2.8 KiB
Markdown
44 lines
2.8 KiB
Markdown
# Head Chunks on Disk Format
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The following describes the format of a chunks file, which is created in the
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`chunks_head/` directory inside the data directory.
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Chunks in the files are referenced from the index by uint64 composed of
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in-file offset (lower 4 bytes) and segment sequence number (upper 4 bytes).
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```
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┌──────────────────────────────┐
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│ magic(0x0130BC91) <4 byte> │
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├──────────────────────────────┤
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│ version(1) <1 byte> │
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├──────────────────────────────┤
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│ padding(0) <3 byte> │
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├──────────────────────────────┤
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│ ┌──────────────────────────┐ │
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│ │ Chunk 1 │ │
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│ ├──────────────────────────┤ │
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│ │ ... │ │
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│ ├──────────────────────────┤ │
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│ │ Chunk N │ │
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│ └──────────────────────────┘ │
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└──────────────────────────────┘
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```
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# Chunk
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Unlike chunks in the on-disk blocks, here we additionally store the series
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reference that each chunk belongs to and the mint/maxt of the chunks. This is
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because we don't have an index associated with these chunks, hence this metadata
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is used while replaying the chunks.
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```
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┌─────────────────────┬───────────────────────┬───────────────────────┬───────────────────┬───────────────┬──────────────┬────────────────┐
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| series ref <8 byte> | mint <8 byte, uint64> | maxt <8 byte, uint64> | encoding <1 byte> | len <uvarint> | data <bytes> │ CRC32 <4 byte> │
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└─────────────────────┴───────────────────────┴───────────────────────┴───────────────────┴───────────────┴──────────────┴────────────────┘
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```
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## OOO encoding
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Head chunks use the highest bit of the `encoding` field to indicate whether it is out-of-order (1) or not (0). This bit is not set for chunks in the on-disk blocks.
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