tupdesc.h

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/*-------------------------------------------------------------------------
 *
 * tupdesc.h
 *    POSTGRES tuple descriptor definitions.
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/tupdesc.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef TUPDESC_H
#define TUPDESC_H
 
#include "access/attnum.h"
#include "catalog/pg_attribute.h"
#include "nodes/pg_list.h"
 
 
typedef struct AttrDefault
{
    AttrNumber  adnum;
    char       *adbin;          /* nodeToString representation of expr */
} AttrDefault;
 
typedef struct ConstrCheck
{
    char       *ccname;
    char       *ccbin;          /* nodeToString representation of expr */
    bool        ccenforced;
    bool        ccvalid;
    bool        ccnoinherit;    /* this is a non-inheritable constraint */
} ConstrCheck;
 
/* This structure contains constraints of a tuple */
typedef struct TupleConstr
{
    AttrDefault *defval;        /* array */
    ConstrCheck *check;         /* array */
    struct AttrMissing *missing;    /* missing attributes values, NULL if none */
    uint16      num_defval;
    uint16      num_check;
    bool        has_not_null;
    bool        has_generated_stored;
} TupleConstr;
 
/*
 * CompactAttribute
 *      Cut-down version of FormData_pg_attribute for faster access for tasks
 *      such as tuple deformation.  The fields of this struct are populated
 *      using the populate_compact_attribute() function, which must be called
 *      directly after the FormData_pg_attribute struct is populated or
 *      altered in any way.
 *
 * Currently, this struct is 16 bytes.  Any code changes which enlarge this
 * struct should be considered very carefully.
 *
 * Code which must access a TupleDesc's attribute data should always make use
 * the fields of this struct when required fields are available here.  It's
 * more efficient to access the memory in CompactAttribute due to it being a
 * more compact representation of FormData_pg_attribute and also because
 * accessing the FormData_pg_attribute requires an additional calculations to
 * obtain the base address of the array within the TupleDesc.
 */
typedef struct CompactAttribute
{
    int32       attcacheoff;    /* fixed offset into tuple, if known, or -1 */
    int16       attlen;         /* attr len in bytes or -1 = varlen, -2 =
                                 * cstring */
    bool        attbyval;       /* as FormData_pg_attribute.attbyval */
    bool        attispackable;  /* FormData_pg_attribute.attstorage !=
                                 * TYPSTORAGE_PLAIN */
    bool        atthasmissing;  /* as FormData_pg_attribute.atthasmissing */
    bool        attisdropped;   /* as FormData_pg_attribute.attisdropped */
    bool        attgenerated;   /* FormData_pg_attribute.attgenerated != '\0' */
    bool        attnotnull;     /* as FormData_pg_attribute.attnotnull */
    uint8       attalignby;     /* alignment requirement in bytes */
} CompactAttribute;
 
/*
 * This struct is passed around within the backend to describe the structure
 * of tuples.  For tuples coming from on-disk relations, the information is
 * collected from the pg_attribute, pg_attrdef, and pg_constraint catalogs.
 * Transient row types (such as the result of a join query) have anonymous
 * TupleDesc structs that generally omit any constraint info; therefore the
 * structure is designed to let the constraints be omitted efficiently.
 *
 * Note that only user attributes, not system attributes, are mentioned in
 * TupleDesc.
 *
 * If the tupdesc is known to correspond to a named rowtype (such as a table's
 * rowtype) then tdtypeid identifies that type and tdtypmod is -1.  Otherwise
 * tdtypeid is RECORDOID, and tdtypmod can be either -1 for a fully anonymous
 * row type, or a value >= 0 to allow the rowtype to be looked up in the
 * typcache.c type cache.
 *
 * Note that tdtypeid is never the OID of a domain over composite, even if
 * we are dealing with values that are known (at some higher level) to be of
 * a domain-over-composite type.  This is because tdtypeid/tdtypmod need to
 * match up with the type labeling of composite Datums, and those are never
 * explicitly marked as being of a domain type, either.
 *
 * Tuple descriptors that live in caches (relcache or typcache, at present)
 * are reference-counted: they can be deleted when their reference count goes
 * to zero.  Tuple descriptors created by the executor need no reference
 * counting, however: they are simply created in the appropriate memory
 * context and go away when the context is freed.  We set the tdrefcount
 * field of such a descriptor to -1, while reference-counted descriptors
 * always have tdrefcount >= 0.
 *
 * Beyond the compact_attrs variable length array, the TupleDesc stores an
 * array of FormData_pg_attribute.  The TupleDescAttr() function, as defined
 * below, takes care of calculating the address of the elements of the
 * FormData_pg_attribute array.
 *
 * The array of CompactAttribute is effectively an abbreviated version of the
 * array of FormData_pg_attribute.  Because CompactAttribute is significantly
 * smaller than FormData_pg_attribute, code, especially performance-critical
 * code, should prioritize using the fields from the CompactAttribute over the
 * equivalent fields in FormData_pg_attribute.
 *
 * Any code making changes manually to and fields in the FormData_pg_attribute
 * array must subsequently call populate_compact_attribute() to flush the
 * changes out to the corresponding 'compact_attrs' element.
 */
typedef struct TupleDescData
{
    int         natts;          /* number of attributes in the tuple */
    Oid         tdtypeid;       /* composite type ID for tuple type */
    int32       tdtypmod;       /* typmod for tuple type */
    int         tdrefcount;     /* reference count, or -1 if not counting */
    TupleConstr *constr;        /* constraints, or NULL if none */
    /* compact_attrs[N] is the compact metadata of Attribute Number N+1 */
    CompactAttribute compact_attrs[FLEXIBLE_ARRAY_MEMBER];
}           TupleDescData;
typedef struct TupleDescData *TupleDesc;
 
extern void populate_compact_attribute(TupleDesc tupdesc, int attnum);
 
/*
 * Calculates the base address of the Form_pg_attribute at the end of the
 * TupleDescData struct.
 */
#define TupleDescAttrAddress(desc) \
    (Form_pg_attribute) ((char *) (desc) + \
     (offsetof(struct TupleDescData, compact_attrs) + \
     (desc)->natts * sizeof(CompactAttribute)))
 
/* Accessor for the i'th FormData_pg_attribute element of tupdesc. */
static inline FormData_pg_attribute *
TupleDescAttr(TupleDesc tupdesc, int i)
{
    FormData_pg_attribute *attrs = TupleDescAttrAddress(tupdesc);
 
    return &attrs[i];
}
 
#undef TupleDescAttrAddress
 
extern void verify_compact_attribute(TupleDesc, int attnum);
 
/*
 * Accessor for the i'th CompactAttribute element of tupdesc.
 */
static inline CompactAttribute *
TupleDescCompactAttr(TupleDesc tupdesc, int i)
{
    CompactAttribute *cattr = &tupdesc->compact_attrs[i];
 
#ifdef USE_ASSERT_CHECKING
 
    /* Check that the CompactAttribute is correctly populated */
    verify_compact_attribute(tupdesc, i);
#endif
 
    return cattr;
}
 
extern TupleDesc CreateTemplateTupleDesc(int natts);
 
extern TupleDesc CreateTupleDesc(int natts, Form_pg_attribute *attrs);
 
extern TupleDesc CreateTupleDescCopy(TupleDesc tupdesc);
 
extern TupleDesc CreateTupleDescTruncatedCopy(TupleDesc tupdesc, int natts);
 
extern TupleDesc CreateTupleDescCopyConstr(TupleDesc tupdesc);
 
#define TupleDescSize(src) \
    (offsetof(struct TupleDescData, compact_attrs) + \
     (src)->natts * sizeof(CompactAttribute) + \
     (src)->natts * sizeof(FormData_pg_attribute))
 
extern void TupleDescCopy(TupleDesc dst, TupleDesc src);
 
extern void TupleDescCopyEntry(TupleDesc dst, AttrNumber dstAttno,
                               TupleDesc src, AttrNumber srcAttno);
 
extern void FreeTupleDesc(TupleDesc tupdesc);
 
extern void IncrTupleDescRefCount(TupleDesc tupdesc);
extern void DecrTupleDescRefCount(TupleDesc tupdesc);
 
#define PinTupleDesc(tupdesc) \
    do { \
        if ((tupdesc)->tdrefcount >= 0) \
            IncrTupleDescRefCount(tupdesc); \
    } while (0)
 
#define ReleaseTupleDesc(tupdesc) \
    do { \
        if ((tupdesc)->tdrefcount >= 0) \
            DecrTupleDescRefCount(tupdesc); \
    } while (0)
 
extern bool equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2);
extern bool equalRowTypes(TupleDesc tupdesc1, TupleDesc tupdesc2);
extern uint32 hashRowType(TupleDesc desc);
 
extern void TupleDescInitEntry(TupleDesc desc,
                               AttrNumber attributeNumber,
                               const char *attributeName,
                               Oid oidtypeid,
                               int32 typmod,
                               int attdim);
 
extern void TupleDescInitBuiltinEntry(TupleDesc desc,
                                      AttrNumber attributeNumber,
                                      const char *attributeName,
                                      Oid oidtypeid,
                                      int32 typmod,
                                      int attdim);
 
extern void TupleDescInitEntryCollation(TupleDesc desc,
                                        AttrNumber attributeNumber,
                                        Oid collationid);
 
extern TupleDesc BuildDescFromLists(const List *names, const List *types, const List *typmods, const List *collations);
 
extern Node *TupleDescGetDefault(TupleDesc tupdesc, AttrNumber attnum);
 
#endif                          /* TUPDESC_H */