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53 lines
1.5 KiB
C++
53 lines
1.5 KiB
C++
#pragma once
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#include <cstdint>
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/** Common Defines */
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#define DBMS_MAX_COMPRESSED_SIZE 0x40000000ULL /// 1GB
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#define COMPRESSED_BLOCK_HEADER_SIZE 9
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namespace DB
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{
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/** Compression method */
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enum class CompressionMethod
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{
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LZ4 = 1,
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LZ4HC = 2, /// The format is the same as for LZ4. The difference is only in compression.
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ZSTD = 3, /// Experimental algorithm: https://github.com/Cyan4973/zstd
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NONE = 4, /// No compression
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};
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/** The compressed block format is as follows:
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*
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* The first 16 bytes are the checksum from all other bytes of the block. Now only CityHash128 is used.
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* In the future, you can provide other checksums, although it will not be possible to make them different in size.
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*
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* The next byte specifies the compression algorithm. Then everything depends on the algorithm.
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*
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* 0x82 - LZ4 or LZ4HC (they have the same format).
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* Next 4 bytes - the size of the compressed data, taking into account the header; 4 bytes is the size of the uncompressed data.
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*
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* NOTE: Why is 0x82?
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* Originally only QuickLZ was used. Then LZ4 was added.
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* The high bit is set to distinguish from QuickLZ, and the second bit is set for compatibility,
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* for the functions qlz_size_compressed, qlz_size_decompressed to work.
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* Although now such compatibility is no longer relevant.
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*
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* 0x90 - ZSTD
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*
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* All sizes are little endian.
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*/
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enum class CompressionMethodByte : uint8_t
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{
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NONE = 0x02,
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LZ4 = 0x82,
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ZSTD = 0x90,
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};
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}
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