src/include/access/detoast.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * detoast.h
   4  *        Access to compressed and external varlena values.
   5  *
   6  * Copyright (c) 2000-2021, PostgreSQL Global Development Group
   7  *
   8  * src/include/access/detoast.h
   9  *
  10  *-------------------------------------------------------------------------
  11  */
  12 #ifndef DETOAST_H
  13 #define DETOAST_H
  14
  15 /*
  16  * Macro to fetch the possibly-unaligned contents of an EXTERNAL datum
  17  * into a local "struct varatt_external" toast pointer.  This should be
  18  * just a memcpy, but some versions of gcc seem to produce broken code
  19  * that assumes the datum contents are aligned.  Introducing an explicit
  20  * intermediate "varattrib_1b_e *" variable seems to fix it.
  21  */
  22 #define VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr) \
  23 do { \
  24         varattrib_1b_e *attre = (varattrib_1b_e *) (attr); \
  25         Assert(VARATT_IS_EXTERNAL(attre)); \
  26         Assert(VARSIZE_EXTERNAL(attre) == sizeof(toast_pointer) + VARHDRSZ_EXTERNAL); \
  27         memcpy(&(toast_pointer), VARDATA_EXTERNAL(attre), sizeof(toast_pointer)); \
  28 } while (0)
  29
  30 /* Size of an EXTERNAL datum that contains a standard TOAST pointer */
  31 #define TOAST_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(varatt_external))
  32
  33 /* Size of an EXTERNAL datum that contains an indirection pointer */
  34 #define INDIRECT_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(varatt_indirect))
  35
  36 /* ----------
  37  * detoast_external_attr() -
  38  *
  39  *              Fetches an external stored attribute from the toast
  40  *              relation. Does NOT decompress it, if stored external
  41  *              in compressed format.
  42  * ----------
  43  */
  44 extern struct varlena *detoast_external_attr(struct varlena *attr);
  45
  46 /* ----------
  47  * detoast_attr() -
  48  *
  49  *              Fully detoasts one attribute, fetching and/or decompressing
  50  *              it as needed.
  51  * ----------
  52  */
  53 extern struct varlena *detoast_attr(struct varlena *attr);
  54
  55 /* ----------
  56  * detoast_attr_slice() -
  57  *
  58  *              Fetches only the specified portion of an attribute.
  59  *              (Handles all cases for attribute storage)
  60  * ----------
  61  */
  62 extern struct varlena *detoast_attr_slice(struct varlena *attr,
  63                                                                                   int32 sliceoffset,
  64                                                                                   int32 slicelength);
  65
  66 /* ----------
  67  * toast_raw_datum_size -
  68  *
  69  *      Return the raw (detoasted) size of a varlena datum
  70  * ----------
  71  */
  72 extern Size toast_raw_datum_size(Datum value);
  73
  74 /* ----------
  75  * toast_datum_size -
  76  *
  77  *      Return the storage size of a varlena datum
  78  * ----------
  79  */
  80 extern Size toast_datum_size(Datum value);
  81
  82 #endif                                                  /* DETOAST_H */