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/*-------------------------------------------------------------------------
*
* detoast.h
* Access to compressed and external varlena values.
*
* Copyright (c) 2000-2020, PostgreSQL Global Development Group
*
* src/include/access/detoast.h
*
*-------------------------------------------------------------------------
*/
#ifndef DETOAST_H
#define DETOAST_H
/*
* Testing whether an externally-stored value is compressed now requires
* comparing extsize (the actual length of the external data) to rawsize
* (the original uncompressed datum's size). The latter includes VARHDRSZ
* overhead, the former doesn't. We never use compression unless it actually
* saves space, so we expect either equality or less-than.
*/
#define VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer) \
((toast_pointer).va_extsize < (toast_pointer).va_rawsize - VARHDRSZ)
/*
* 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 */
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