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Diffstat (limited to 'src/include/access/detoast.h')
-rw-r--r-- | src/include/access/detoast.h | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/src/include/access/detoast.h b/src/include/access/detoast.h new file mode 100644 index 0000000..773a02f --- /dev/null +++ b/src/include/access/detoast.h @@ -0,0 +1,82 @@ +/*------------------------------------------------------------------------- + * + * detoast.h + * Access to compressed and external varlena values. + * + * Copyright (c) 2000-2021, PostgreSQL Global Development Group + * + * src/include/access/detoast.h + * + *------------------------------------------------------------------------- + */ +#ifndef DETOAST_H +#define DETOAST_H + +/* + * Macro to fetch the possibly-unaligned contents of an EXTERNAL datum + * into a local "struct varatt_external" toast pointer. This should be + * just a memcpy, but some versions of gcc seem to produce broken code + * that assumes the datum contents are aligned. Introducing an explicit + * intermediate "varattrib_1b_e *" variable seems to fix it. + */ +#define VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr) \ +do { \ + varattrib_1b_e *attre = (varattrib_1b_e *) (attr); \ + Assert(VARATT_IS_EXTERNAL(attre)); \ + Assert(VARSIZE_EXTERNAL(attre) == sizeof(toast_pointer) + VARHDRSZ_EXTERNAL); \ + memcpy(&(toast_pointer), VARDATA_EXTERNAL(attre), sizeof(toast_pointer)); \ +} while (0) + +/* Size of an EXTERNAL datum that contains a standard TOAST pointer */ +#define TOAST_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(varatt_external)) + +/* Size of an EXTERNAL datum that contains an indirection pointer */ +#define INDIRECT_POINTER_SIZE (VARHDRSZ_EXTERNAL + sizeof(varatt_indirect)) + +/* ---------- + * detoast_external_attr() - + * + * Fetches an external stored attribute from the toast + * relation. Does NOT decompress it, if stored external + * in compressed format. + * ---------- + */ +extern struct varlena *detoast_external_attr(struct varlena *attr); + +/* ---------- + * detoast_attr() - + * + * Fully detoasts one attribute, fetching and/or decompressing + * it as needed. + * ---------- + */ +extern struct varlena *detoast_attr(struct varlena *attr); + +/* ---------- + * detoast_attr_slice() - + * + * Fetches only the specified portion of an attribute. + * (Handles all cases for attribute storage) + * ---------- + */ +extern struct varlena *detoast_attr_slice(struct varlena *attr, + int32 sliceoffset, + int32 slicelength); + +/* ---------- + * toast_raw_datum_size - + * + * Return the raw (detoasted) size of a varlena datum + * ---------- + */ +extern Size toast_raw_datum_size(Datum value); + +/* ---------- + * toast_datum_size - + * + * Return the storage size of a varlena datum + * ---------- + */ +extern Size toast_datum_size(Datum value); + +#endif /* DETOAST_H */ |