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e6241d8e03
Redefine '\0' (InvalidCompressionMethod) as meaning "if we need to compress, use the current setting of default_toast_compression". This allows '\0' to be a suitable default choice regardless of datatype, greatly simplifying code paths that initialize tupledescs and the like. It seems like a more user-friendly approach as well, because now the default compression choice doesn't migrate into table definitions, meaning that changing default_toast_compression is usually sufficient to flip an installation's behavior; one needn't tediously issue per-column ALTER SET COMPRESSION commands. Along the way, fix a few minor bugs and documentation issues with the per-column-compression feature. Adopt more robust APIs for SetIndexStorageProperties and GetAttributeCompression. Bump catversion because typical contents of attcompression will now be different. We could get away without doing that, but it seems better to ensure v14 installations all agree on this. (We already forced initdb for beta2, anyway.) Discussion: https://postgr.es/m/626613.1621787110@sss.pgh.pa.us
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, 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 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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