src/include/access/toast_compression.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * toast_compression.h
   4  *        Functions for toast compression.
   5  *
   6  * Copyright (c) 2021, PostgreSQL Global Development Group
   7  *
   8  * src/include/access/toast_compression.h
   9  *
  10  *-------------------------------------------------------------------------
  11  */
  12
  13 #ifndef TOAST_COMPRESSION_H
  14 #define TOAST_COMPRESSION_H
  15
  16 /*
  17  * GUC support.
  18  *
  19  * default_toast_compression is an integer for purposes of the GUC machinery,
  20  * but the value is one of the char values defined below, as they appear in
  21  * pg_attribute.attcompression, e.g. TOAST_PGLZ_COMPRESSION.
  22  */
  23 extern int      default_toast_compression;
  24
  25 /*
  26  * Built-in compression method ID.  The toast compression header will store
  27  * this in the first 2 bits of the raw length.  These built-in compression
  28  * method IDs are directly mapped to the built-in compression methods.
  29  *
  30  * Don't use these values for anything other than understanding the meaning
  31  * of the raw bits from a varlena; in particular, if the goal is to identify
  32  * a compression method, use the constants TOAST_PGLZ_COMPRESSION, etc.
  33  * below. We might someday support more than 4 compression methods, but
  34  * we can never have more than 4 values in this enum, because there are
  35  * only 2 bits available in the places where this is stored.
  36  */
  37 typedef enum ToastCompressionId
  38 {
  39         TOAST_PGLZ_COMPRESSION_ID = 0,
  40         TOAST_LZ4_COMPRESSION_ID = 1,
  41         TOAST_INVALID_COMPRESSION_ID = 2
  42 } ToastCompressionId;
  43
  44 /*
  45  * Built-in compression methods.  pg_attribute will store these in the
  46  * attcompression column.  In attcompression, InvalidCompressionMethod
  47  * denotes the default behavior.
  48  */
  49 #define TOAST_PGLZ_COMPRESSION                  'p'
  50 #define TOAST_LZ4_COMPRESSION                   'l'
  51 #define InvalidCompressionMethod                '\0'
  52
  53 #define CompressionMethodIsValid(cm)  ((cm) != InvalidCompressionMethod)
  54
  55
  56 /* pglz compression/decompression routines */
  57 extern struct varlena *pglz_compress_datum(const struct varlena *value);
  58 extern struct varlena *pglz_decompress_datum(const struct varlena *value);
  59 extern struct varlena *pglz_decompress_datum_slice(const struct varlena *value,
  60                                                                                                    int32 slicelength);
  61
  62 /* lz4 compression/decompression routines */
  63 extern struct varlena *lz4_compress_datum(const struct varlena *value);
  64 extern struct varlena *lz4_decompress_datum(const struct varlena *value);
  65 extern struct varlena *lz4_decompress_datum_slice(const struct varlena *value,
  66                                                                                                   int32 slicelength);
  67
  68 /* other stuff */
  69 extern ToastCompressionId toast_get_compression_id(struct varlena *attr);
  70 extern char CompressionNameToMethod(const char *compression);
  71 extern const char *GetCompressionMethodName(char method);
  72
  73 #endif                                                  /* TOAST_COMPRESSION_H */