74 lines
2.7 KiB
C
74 lines
2.7 KiB
C
/*-------------------------------------------------------------------------
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*
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* toast_compression.h
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* Functions for toast compression.
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*
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* Copyright (c) 2021-2023, PostgreSQL Global Development Group
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*
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* src/include/access/toast_compression.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef TOAST_COMPRESSION_H
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#define TOAST_COMPRESSION_H
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/*
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* GUC support.
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*
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* default_toast_compression is an integer for purposes of the GUC machinery,
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* but the value is one of the char values defined below, as they appear in
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* pg_attribute.attcompression, e.g. TOAST_PGLZ_COMPRESSION.
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*/
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extern PGDLLIMPORT int default_toast_compression;
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/*
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* Built-in compression method ID. The toast compression header will store
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* this in the first 2 bits of the raw length. These built-in compression
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* method IDs are directly mapped to the built-in compression methods.
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*
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* Don't use these values for anything other than understanding the meaning
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* of the raw bits from a varlena; in particular, if the goal is to identify
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* a compression method, use the constants TOAST_PGLZ_COMPRESSION, etc.
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* below. We might someday support more than 4 compression methods, but
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* we can never have more than 4 values in this enum, because there are
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* only 2 bits available in the places where this is stored.
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*/
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typedef enum ToastCompressionId
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{
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TOAST_PGLZ_COMPRESSION_ID = 0,
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TOAST_LZ4_COMPRESSION_ID = 1,
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TOAST_INVALID_COMPRESSION_ID = 2,
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} ToastCompressionId;
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/*
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* Built-in compression methods. pg_attribute will store these in the
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* attcompression column. In attcompression, InvalidCompressionMethod
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* denotes the default behavior.
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*/
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#define TOAST_PGLZ_COMPRESSION 'p'
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#define TOAST_LZ4_COMPRESSION 'l'
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#define InvalidCompressionMethod '\0'
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#define CompressionMethodIsValid(cm) ((cm) != InvalidCompressionMethod)
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/* pglz compression/decompression routines */
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extern struct varlena *pglz_compress_datum(const struct varlena *value);
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extern struct varlena *pglz_decompress_datum(const struct varlena *value);
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extern struct varlena *pglz_decompress_datum_slice(const struct varlena *value,
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int32 slicelength);
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/* lz4 compression/decompression routines */
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extern struct varlena *lz4_compress_datum(const struct varlena *value);
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extern struct varlena *lz4_decompress_datum(const struct varlena *value);
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extern struct varlena *lz4_decompress_datum_slice(const struct varlena *value,
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int32 slicelength);
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/* other stuff */
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extern ToastCompressionId toast_get_compression_id(struct varlena *attr);
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extern char CompressionNameToMethod(const char *compression);
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extern const char *GetCompressionMethodName(char method);
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#endif /* TOAST_COMPRESSION_H */
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