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