tupdesc.c

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/*-------------------------------------------------------------------------
 *
 * tupdesc.c
 *    POSTGRES tuple descriptor support code
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/common/tupdesc.c
 *
 * NOTES
 *    some of the executor utility code such as "ExecTypeFromTL" should be
 *    moved here.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/htup_details.h"
#include "access/toast_compression.h"
#include "access/tupdesc_details.h"
#include "catalog/catalog.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_type.h"
#include "common/hashfn.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/resowner.h"
#include "utils/syscache.h"
 
/* ResourceOwner callbacks to hold tupledesc references  */
static void ResOwnerReleaseTupleDesc(Datum res);
static char *ResOwnerPrintTupleDesc(Datum res);
 
static const ResourceOwnerDesc tupdesc_resowner_desc =
{
    .name = "tupdesc reference",
    .release_phase = RESOURCE_RELEASE_AFTER_LOCKS,
    .release_priority = RELEASE_PRIO_TUPDESC_REFS,
    .ReleaseResource = ResOwnerReleaseTupleDesc,
    .DebugPrint = ResOwnerPrintTupleDesc
};
 
/* Convenience wrappers over ResourceOwnerRemember/Forget */
static inline void
ResourceOwnerRememberTupleDesc(ResourceOwner owner, TupleDesc tupdesc)
{
    ResourceOwnerRemember(owner, PointerGetDatum(tupdesc), &tupdesc_resowner_desc);
}
 
static inline void
ResourceOwnerForgetTupleDesc(ResourceOwner owner, TupleDesc tupdesc)
{
    ResourceOwnerForget(owner, PointerGetDatum(tupdesc), &tupdesc_resowner_desc);
}
 
/*
 * populate_compact_attribute_internal
 *      Helper function for populate_compact_attribute()
 */
static inline void
populate_compact_attribute_internal(Form_pg_attribute src,
                                    CompactAttribute *dst)
{
    memset(dst, 0, sizeof(CompactAttribute));
 
    dst->attcacheoff = -1;
    dst->attlen = src->attlen;
 
    dst->attbyval = src->attbyval;
    dst->attispackable = (src->attstorage != TYPSTORAGE_PLAIN);
    dst->atthasmissing = src->atthasmissing;
    dst->attisdropped = src->attisdropped;
    dst->attgenerated = (src->attgenerated != '\0');
 
    /*
     * Assign nullability status for this column.  Assuming that a constraint
     * exists, at this point we don't know if a not-null constraint is valid,
     * so we assign UNKNOWN unless the table is a catalog, in which case we
     * know it's valid.
     */
    dst->attnullability = !src->attnotnull ? ATTNULLABLE_UNRESTRICTED :
        IsCatalogRelationOid(src->attrelid) ? ATTNULLABLE_VALID :
        ATTNULLABLE_UNKNOWN;
 
    switch (src->attalign)
    {
        case TYPALIGN_INT:
            dst->attalignby = ALIGNOF_INT;
            break;
        case TYPALIGN_CHAR:
            dst->attalignby = sizeof(char);
            break;
        case TYPALIGN_DOUBLE:
            dst->attalignby = ALIGNOF_DOUBLE;
            break;
        case TYPALIGN_SHORT:
            dst->attalignby = ALIGNOF_SHORT;
            break;
        default:
            dst->attalignby = 0;
            elog(ERROR, "invalid attalign value: %c", src->attalign);
            break;
    }
}
 
/*
 * populate_compact_attribute
 *      Fill in the corresponding CompactAttribute element from the
 *      Form_pg_attribute for the given attribute number.  This must be called
 *      whenever a change is made to a Form_pg_attribute in the TupleDesc.
 */
void
populate_compact_attribute(TupleDesc tupdesc, int attnum)
{
    Form_pg_attribute src = TupleDescAttr(tupdesc, attnum);
    CompactAttribute *dst;
 
    /*
     * Don't use TupleDescCompactAttr to prevent infinite recursion in assert
     * builds.
     */
    dst = &tupdesc->compact_attrs[attnum];
 
    populate_compact_attribute_internal(src, dst);
}
 
/*
 * verify_compact_attribute
 *      In Assert enabled builds, we verify that the CompactAttribute is
 *      populated correctly.  This helps find bugs in places such as ALTER
 *      TABLE where code makes changes to the FormData_pg_attribute but
 *      forgets to call populate_compact_attribute().
 *
 * This is used in TupleDescCompactAttr(), but declared here to allow access
 * to populate_compact_attribute_internal().
 */
void
verify_compact_attribute(TupleDesc tupdesc, int attnum)
{
#ifdef USE_ASSERT_CHECKING
    CompactAttribute cattr;
    Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum);
    CompactAttribute tmp;
 
    /*
     * Make a temp copy of the TupleDesc's CompactAttribute.  This may be a
     * shared TupleDesc and the attcacheoff might get changed by another
     * backend.
     */
    memcpy(&cattr, &tupdesc->compact_attrs[attnum], sizeof(CompactAttribute));
 
    /*
     * Populate the temporary CompactAttribute from the corresponding
     * Form_pg_attribute
     */
    populate_compact_attribute_internal(attr, &tmp);
 
    /*
     * Make the attcacheoff match since it's been reset to -1 by
     * populate_compact_attribute_internal.  Same with attnullability.
     */
    tmp.attcacheoff = cattr.attcacheoff;
    tmp.attnullability = cattr.attnullability;
 
    /* Check the freshly populated CompactAttribute matches the TupleDesc's */
    Assert(memcmp(&tmp, &cattr, sizeof(CompactAttribute)) == 0);
#endif
}
 
/*
 * CreateTemplateTupleDesc
 *      This function allocates an empty tuple descriptor structure.
 *
 * Tuple type ID information is initially set for an anonymous record type;
 * caller can overwrite this if needed.
 */
TupleDesc
CreateTemplateTupleDesc(int natts)
{
    TupleDesc   desc;
 
    /*
     * sanity checks
     */
    Assert(natts >= 0);
 
    /*
     * Allocate enough memory for the tuple descriptor, the CompactAttribute
     * array and also an array of FormData_pg_attribute.
     *
     * Note: the FormData_pg_attribute array stride is
     * sizeof(FormData_pg_attribute), since we declare the array elements as
     * FormData_pg_attribute for notational convenience.  However, we only
     * guarantee that the first ATTRIBUTE_FIXED_PART_SIZE bytes of each entry
     * are valid; most code that copies tupdesc entries around copies just
     * that much.  In principle that could be less due to trailing padding,
     * although with the current definition of pg_attribute there probably
     * isn't any padding.
     */
    desc = (TupleDesc) palloc(offsetof(struct TupleDescData, compact_attrs) +
                              natts * sizeof(CompactAttribute) +
                              natts * sizeof(FormData_pg_attribute));
 
    /*
     * Initialize other fields of the tupdesc.
     */
    desc->natts = natts;
    desc->constr = NULL;
    desc->tdtypeid = RECORDOID;
    desc->tdtypmod = -1;
    desc->tdrefcount = -1;      /* assume not reference-counted */
 
    return desc;
}
 
/*
 * CreateTupleDesc
 *      This function allocates a new TupleDesc by copying a given
 *      Form_pg_attribute array.
 *
 * Tuple type ID information is initially set for an anonymous record type;
 * caller can overwrite this if needed.
 */
TupleDesc
CreateTupleDesc(int natts, Form_pg_attribute *attrs)
{
    TupleDesc   desc;
    int         i;
 
    desc = CreateTemplateTupleDesc(natts);
 
    for (i = 0; i < natts; ++i)
    {
        memcpy(TupleDescAttr(desc, i), attrs[i], ATTRIBUTE_FIXED_PART_SIZE);
        populate_compact_attribute(desc, i);
    }
    return desc;
}
 
/*
 * CreateTupleDescCopy
 *      This function creates a new TupleDesc by copying from an existing
 *      TupleDesc.
 *
 * !!! Constraints and defaults are not copied !!!
 */
TupleDesc
CreateTupleDescCopy(TupleDesc tupdesc)
{
    TupleDesc   desc;
    int         i;
 
    desc = CreateTemplateTupleDesc(tupdesc->natts);
 
    /* Flat-copy the attribute array */
    memcpy(TupleDescAttr(desc, 0),
           TupleDescAttr(tupdesc, 0),
           desc->natts * sizeof(FormData_pg_attribute));
 
    /*
     * Since we're not copying constraints and defaults, clear fields
     * associated with them.
     */
    for (i = 0; i < desc->natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(desc, i);
 
        att->attnotnull = false;
        att->atthasdef = false;
        att->atthasmissing = false;
        att->attidentity = '\0';
        att->attgenerated = '\0';
 
        populate_compact_attribute(desc, i);
    }
 
    /* We can copy the tuple type identification, too */
    desc->tdtypeid = tupdesc->tdtypeid;
    desc->tdtypmod = tupdesc->tdtypmod;
 
    return desc;
}
 
/*
 * CreateTupleDescTruncatedCopy
 *      This function creates a new TupleDesc with only the first 'natts'
 *      attributes from an existing TupleDesc
 *
 * !!! Constraints and defaults are not copied !!!
 */
TupleDesc
CreateTupleDescTruncatedCopy(TupleDesc tupdesc, int natts)
{
    TupleDesc   desc;
    int         i;
 
    Assert(natts <= tupdesc->natts);
 
    desc = CreateTemplateTupleDesc(natts);
 
    /* Flat-copy the attribute array */
    memcpy(TupleDescAttr(desc, 0),
           TupleDescAttr(tupdesc, 0),
           desc->natts * sizeof(FormData_pg_attribute));
 
    /*
     * Since we're not copying constraints and defaults, clear fields
     * associated with them.
     */
    for (i = 0; i < desc->natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(desc, i);
 
        att->attnotnull = false;
        att->atthasdef = false;
        att->atthasmissing = false;
        att->attidentity = '\0';
        att->attgenerated = '\0';
 
        populate_compact_attribute(desc, i);
    }
 
    /* We can copy the tuple type identification, too */
    desc->tdtypeid = tupdesc->tdtypeid;
    desc->tdtypmod = tupdesc->tdtypmod;
 
    return desc;
}
 
/*
 * CreateTupleDescCopyConstr
 *      This function creates a new TupleDesc by copying from an existing
 *      TupleDesc (including its constraints and defaults).
 */
TupleDesc
CreateTupleDescCopyConstr(TupleDesc tupdesc)
{
    TupleDesc   desc;
    TupleConstr *constr = tupdesc->constr;
    int         i;
 
    desc = CreateTemplateTupleDesc(tupdesc->natts);
 
    /* Flat-copy the attribute array */
    memcpy(TupleDescAttr(desc, 0),
           TupleDescAttr(tupdesc, 0),
           desc->natts * sizeof(FormData_pg_attribute));
 
    for (i = 0; i < desc->natts; i++)
    {
        populate_compact_attribute(desc, i);
 
        TupleDescCompactAttr(desc, i)->attnullability =
            TupleDescCompactAttr(tupdesc, i)->attnullability;
    }
 
    /* Copy the TupleConstr data structure, if any */
    if (constr)
    {
        TupleConstr *cpy = (TupleConstr *) palloc0(sizeof(TupleConstr));
 
        cpy->has_not_null = constr->has_not_null;
        cpy->has_generated_stored = constr->has_generated_stored;
        cpy->has_generated_virtual = constr->has_generated_virtual;
 
        if ((cpy->num_defval = constr->num_defval) > 0)
        {
            cpy->defval = (AttrDefault *) palloc(cpy->num_defval * sizeof(AttrDefault));
            memcpy(cpy->defval, constr->defval, cpy->num_defval * sizeof(AttrDefault));
            for (i = cpy->num_defval - 1; i >= 0; i--)
                cpy->defval[i].adbin = pstrdup(constr->defval[i].adbin);
        }
 
        if (constr->missing)
        {
            cpy->missing = (AttrMissing *) palloc(tupdesc->natts * sizeof(AttrMissing));
            memcpy(cpy->missing, constr->missing, tupdesc->natts * sizeof(AttrMissing));
            for (i = tupdesc->natts - 1; i >= 0; i--)
            {
                if (constr->missing[i].am_present)
                {
                    CompactAttribute *attr = TupleDescCompactAttr(tupdesc, i);
 
                    cpy->missing[i].am_value = datumCopy(constr->missing[i].am_value,
                                                         attr->attbyval,
                                                         attr->attlen);
                }
            }
        }
 
        if ((cpy->num_check = constr->num_check) > 0)
        {
            cpy->check = (ConstrCheck *) palloc(cpy->num_check * sizeof(ConstrCheck));
            memcpy(cpy->check, constr->check, cpy->num_check * sizeof(ConstrCheck));
            for (i = cpy->num_check - 1; i >= 0; i--)
            {
                cpy->check[i].ccname = pstrdup(constr->check[i].ccname);
                cpy->check[i].ccbin = pstrdup(constr->check[i].ccbin);
                cpy->check[i].ccenforced = constr->check[i].ccenforced;
                cpy->check[i].ccvalid = constr->check[i].ccvalid;
                cpy->check[i].ccnoinherit = constr->check[i].ccnoinherit;
            }
        }
 
        desc->constr = cpy;
    }
 
    /* We can copy the tuple type identification, too */
    desc->tdtypeid = tupdesc->tdtypeid;
    desc->tdtypmod = tupdesc->tdtypmod;
 
    return desc;
}
 
/*
 * TupleDescCopy
 *      Copy a tuple descriptor into caller-supplied memory.
 *      The memory may be shared memory mapped at any address, and must
 *      be sufficient to hold TupleDescSize(src) bytes.
 *
 * !!! Constraints and defaults are not copied !!!
 */
void
TupleDescCopy(TupleDesc dst, TupleDesc src)
{
    int         i;
 
    /* Flat-copy the header and attribute arrays */
    memcpy(dst, src, TupleDescSize(src));
 
    /*
     * Since we're not copying constraints and defaults, clear fields
     * associated with them.
     */
    for (i = 0; i < dst->natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(dst, i);
 
        att->attnotnull = false;
        att->atthasdef = false;
        att->atthasmissing = false;
        att->attidentity = '\0';
        att->attgenerated = '\0';
 
        populate_compact_attribute(dst, i);
    }
    dst->constr = NULL;
 
    /*
     * Also, assume the destination is not to be ref-counted.  (Copying the
     * source's refcount would be wrong in any case.)
     */
    dst->tdrefcount = -1;
}
 
/*
 * TupleDescCopyEntry
 *      This function copies a single attribute structure from one tuple
 *      descriptor to another.
 *
 * !!! Constraints and defaults are not copied !!!
 */
void
TupleDescCopyEntry(TupleDesc dst, AttrNumber dstAttno,
                   TupleDesc src, AttrNumber srcAttno)
{
    Form_pg_attribute dstAtt = TupleDescAttr(dst, dstAttno - 1);
    Form_pg_attribute srcAtt = TupleDescAttr(src, srcAttno - 1);
 
    /*
     * sanity checks
     */
    Assert(src);
    Assert(dst);
    Assert(srcAttno >= 1);
    Assert(srcAttno <= src->natts);
    Assert(dstAttno >= 1);
    Assert(dstAttno <= dst->natts);
 
    memcpy(dstAtt, srcAtt, ATTRIBUTE_FIXED_PART_SIZE);
 
    dstAtt->attnum = dstAttno;
 
    /* since we're not copying constraints or defaults, clear these */
    dstAtt->attnotnull = false;
    dstAtt->atthasdef = false;
    dstAtt->atthasmissing = false;
    dstAtt->attidentity = '\0';
    dstAtt->attgenerated = '\0';
 
    populate_compact_attribute(dst, dstAttno - 1);
}
 
/*
 * Free a TupleDesc including all substructure
 */
void
FreeTupleDesc(TupleDesc tupdesc)
{
    int         i;
 
    /*
     * Possibly this should assert tdrefcount == 0, to disallow explicit
     * freeing of un-refcounted tupdescs?
     */
    Assert(tupdesc->tdrefcount <= 0);
 
    if (tupdesc->constr)
    {
        if (tupdesc->constr->num_defval > 0)
        {
            AttrDefault *attrdef = tupdesc->constr->defval;
 
            for (i = tupdesc->constr->num_defval - 1; i >= 0; i--)
                pfree(attrdef[i].adbin);
            pfree(attrdef);
        }
        if (tupdesc->constr->missing)
        {
            AttrMissing *attrmiss = tupdesc->constr->missing;
 
            for (i = tupdesc->natts - 1; i >= 0; i--)
            {
                if (attrmiss[i].am_present
                    && !TupleDescAttr(tupdesc, i)->attbyval)
                    pfree(DatumGetPointer(attrmiss[i].am_value));
            }
            pfree(attrmiss);
        }
        if (tupdesc->constr->num_check > 0)
        {
            ConstrCheck *check = tupdesc->constr->check;
 
            for (i = tupdesc->constr->num_check - 1; i >= 0; i--)
            {
                pfree(check[i].ccname);
                pfree(check[i].ccbin);
            }
            pfree(check);
        }
        pfree(tupdesc->constr);
    }
 
    pfree(tupdesc);
}
 
/*
 * Increment the reference count of a tupdesc, and log the reference in
 * CurrentResourceOwner.
 *
 * Do not apply this to tupdescs that are not being refcounted.  (Use the
 * macro PinTupleDesc for tupdescs of uncertain status.)
 */
void
IncrTupleDescRefCount(TupleDesc tupdesc)
{
    Assert(tupdesc->tdrefcount >= 0);
 
    ResourceOwnerEnlarge(CurrentResourceOwner);
    tupdesc->tdrefcount++;
    ResourceOwnerRememberTupleDesc(CurrentResourceOwner, tupdesc);
}
 
/*
 * Decrement the reference count of a tupdesc, remove the corresponding
 * reference from CurrentResourceOwner, and free the tupdesc if no more
 * references remain.
 *
 * Do not apply this to tupdescs that are not being refcounted.  (Use the
 * macro ReleaseTupleDesc for tupdescs of uncertain status.)
 */
void
DecrTupleDescRefCount(TupleDesc tupdesc)
{
    Assert(tupdesc->tdrefcount > 0);
 
    ResourceOwnerForgetTupleDesc(CurrentResourceOwner, tupdesc);
    if (--tupdesc->tdrefcount == 0)
        FreeTupleDesc(tupdesc);
}
 
/*
 * Compare two TupleDesc structures for logical equality
 */
bool
equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)
{
    int         i,
                n;
 
    if (tupdesc1->natts != tupdesc2->natts)
        return false;
    if (tupdesc1->tdtypeid != tupdesc2->tdtypeid)
        return false;
 
    /* tdtypmod and tdrefcount are not checked */
 
    for (i = 0; i < tupdesc1->natts; i++)
    {
        Form_pg_attribute attr1 = TupleDescAttr(tupdesc1, i);
        Form_pg_attribute attr2 = TupleDescAttr(tupdesc2, i);
 
        /*
         * We do not need to check every single field here: we can disregard
         * attrelid and attnum (which were used to place the row in the attrs
         * array in the first place).  It might look like we could dispense
         * with checking attlen/attbyval/attalign, since these are derived
         * from atttypid; but in the case of dropped columns we must check
         * them (since atttypid will be zero for all dropped columns) and in
         * general it seems safer to check them always.
         *
         * We intentionally ignore atthasmissing, since that's not very
         * relevant in tupdescs, which lack the attmissingval field.
         */
        if (strcmp(NameStr(attr1->attname), NameStr(attr2->attname)) != 0)
            return false;
        if (attr1->atttypid != attr2->atttypid)
            return false;
        if (attr1->attlen != attr2->attlen)
            return false;
        if (attr1->attndims != attr2->attndims)
            return false;
        if (attr1->atttypmod != attr2->atttypmod)
            return false;
        if (attr1->attbyval != attr2->attbyval)
            return false;
        if (attr1->attalign != attr2->attalign)
            return false;
        if (attr1->attstorage != attr2->attstorage)
            return false;
        if (attr1->attcompression != attr2->attcompression)
            return false;
        if (attr1->attnotnull != attr2->attnotnull)
            return false;
 
        /*
         * When the column has a not-null constraint, we also need to consider
         * its validity aspect, which only manifests in CompactAttribute->
         * attnullability, so verify that.
         */
        if (attr1->attnotnull)
        {
            CompactAttribute *cattr1 = TupleDescCompactAttr(tupdesc1, i);
            CompactAttribute *cattr2 = TupleDescCompactAttr(tupdesc2, i);
 
            Assert(cattr1->attnullability != ATTNULLABLE_UNKNOWN);
            Assert((cattr1->attnullability == ATTNULLABLE_UNKNOWN) ==
                   (cattr2->attnullability == ATTNULLABLE_UNKNOWN));
 
            if (cattr1->attnullability != cattr2->attnullability)
                return false;
        }
        if (attr1->atthasdef != attr2->atthasdef)
            return false;
        if (attr1->attidentity != attr2->attidentity)
            return false;
        if (attr1->attgenerated != attr2->attgenerated)
            return false;
        if (attr1->attisdropped != attr2->attisdropped)
            return false;
        if (attr1->attislocal != attr2->attislocal)
            return false;
        if (attr1->attinhcount != attr2->attinhcount)
            return false;
        if (attr1->attcollation != attr2->attcollation)
            return false;
        /* variable-length fields are not even present... */
    }
 
    if (tupdesc1->constr != NULL)
    {
        TupleConstr *constr1 = tupdesc1->constr;
        TupleConstr *constr2 = tupdesc2->constr;
 
        if (constr2 == NULL)
            return false;
        if (constr1->has_not_null != constr2->has_not_null)
            return false;
        if (constr1->has_generated_stored != constr2->has_generated_stored)
            return false;
        if (constr1->has_generated_virtual != constr2->has_generated_virtual)
            return false;
        n = constr1->num_defval;
        if (n != (int) constr2->num_defval)
            return false;
        /* We assume here that both AttrDefault arrays are in adnum order */
        for (i = 0; i < n; i++)
        {
            AttrDefault *defval1 = constr1->defval + i;
            AttrDefault *defval2 = constr2->defval + i;
 
            if (defval1->adnum != defval2->adnum)
                return false;
            if (strcmp(defval1->adbin, defval2->adbin) != 0)
                return false;
        }
        if (constr1->missing)
        {
            if (!constr2->missing)
                return false;
            for (i = 0; i < tupdesc1->natts; i++)
            {
                AttrMissing *missval1 = constr1->missing + i;
                AttrMissing *missval2 = constr2->missing + i;
 
                if (missval1->am_present != missval2->am_present)
                    return false;
                if (missval1->am_present)
                {
                    CompactAttribute *missatt1 = TupleDescCompactAttr(tupdesc1, i);
 
                    if (!datumIsEqual(missval1->am_value, missval2->am_value,
                                      missatt1->attbyval, missatt1->attlen))
                        return false;
                }
            }
        }
        else if (constr2->missing)
            return false;
        n = constr1->num_check;
        if (n != (int) constr2->num_check)
            return false;
 
        /*
         * Similarly, we rely here on the ConstrCheck entries being sorted by
         * name.  If there are duplicate names, the outcome of the comparison
         * is uncertain, but that should not happen.
         */
        for (i = 0; i < n; i++)
        {
            ConstrCheck *check1 = constr1->check + i;
            ConstrCheck *check2 = constr2->check + i;
 
            if (!(strcmp(check1->ccname, check2->ccname) == 0 &&
                  strcmp(check1->ccbin, check2->ccbin) == 0 &&
                  check1->ccenforced == check2->ccenforced &&
                  check1->ccvalid == check2->ccvalid &&
                  check1->ccnoinherit == check2->ccnoinherit))
                return false;
        }
    }
    else if (tupdesc2->constr != NULL)
        return false;
    return true;
}
 
/*
 * equalRowTypes
 *
 * This determines whether two tuple descriptors have equal row types.  This
 * only checks those fields in pg_attribute that are applicable for row types,
 * while ignoring those fields that define the physical row storage or those
 * that define table column metadata.
 *
 * Specifically, this checks:
 *
 * - same number of attributes
 * - same composite type ID (but could both be zero)
 * - corresponding attributes (in order) have same the name, type, typmod,
 *   collation
 *
 * This is used to check whether two record types are compatible, whether
 * function return row types are the same, and other similar situations.
 *
 * (XXX There was some discussion whether attndims should be checked here, but
 * for now it has been decided not to.)
 *
 * Note: We deliberately do not check the tdtypmod field.  This allows
 * typcache.c to use this routine to see if a cached record type matches a
 * requested type.
 */
bool
equalRowTypes(TupleDesc tupdesc1, TupleDesc tupdesc2)
{
    if (tupdesc1->natts != tupdesc2->natts)
        return false;
    if (tupdesc1->tdtypeid != tupdesc2->tdtypeid)
        return false;
 
    for (int i = 0; i < tupdesc1->natts; i++)
    {
        Form_pg_attribute attr1 = TupleDescAttr(tupdesc1, i);
        Form_pg_attribute attr2 = TupleDescAttr(tupdesc2, i);
 
        if (strcmp(NameStr(attr1->attname), NameStr(attr2->attname)) != 0)
            return false;
        if (attr1->atttypid != attr2->atttypid)
            return false;
        if (attr1->atttypmod != attr2->atttypmod)
            return false;
        if (attr1->attcollation != attr2->attcollation)
            return false;
 
        /* Record types derived from tables could have dropped fields. */
        if (attr1->attisdropped != attr2->attisdropped)
            return false;
    }
 
    return true;
}
 
/*
 * hashRowType
 *
 * If two tuple descriptors would be considered equal by equalRowTypes()
 * then their hash value will be equal according to this function.
 */
uint32
hashRowType(TupleDesc desc)
{
    uint32      s;
    int         i;
 
    s = hash_combine(0, hash_bytes_uint32(desc->natts));
    s = hash_combine(s, hash_bytes_uint32(desc->tdtypeid));
    for (i = 0; i < desc->natts; ++i)
        s = hash_combine(s, hash_bytes_uint32(TupleDescAttr(desc, i)->atttypid));
 
    return s;
}
 
/*
 * TupleDescInitEntry
 *      This function initializes a single attribute structure in
 *      a previously allocated tuple descriptor.
 *
 * If attributeName is NULL, the attname field is set to an empty string
 * (this is for cases where we don't know or need a name for the field).
 * Also, some callers use this function to change the datatype-related fields
 * in an existing tupdesc; they pass attributeName = NameStr(att->attname)
 * to indicate that the attname field shouldn't be modified.
 *
 * Note that attcollation is set to the default for the specified datatype.
 * If a nondefault collation is needed, insert it afterwards using
 * TupleDescInitEntryCollation.
 */
void
TupleDescInitEntry(TupleDesc desc,
                   AttrNumber attributeNumber,
                   const char *attributeName,
                   Oid oidtypeid,
                   int32 typmod,
                   int attdim)
{
    HeapTuple   tuple;
    Form_pg_type typeForm;
    Form_pg_attribute att;
 
    /*
     * sanity checks
     */
    Assert(desc);
    Assert(attributeNumber >= 1);
    Assert(attributeNumber <= desc->natts);
    Assert(attdim >= 0);
    Assert(attdim <= PG_INT16_MAX);
 
    /*
     * initialize the attribute fields
     */
    att = TupleDescAttr(desc, attributeNumber - 1);
 
    att->attrelid = 0;          /* dummy value */
 
    /*
     * Note: attributeName can be NULL, because the planner doesn't always
     * fill in valid resname values in targetlists, particularly for resjunk
     * attributes. Also, do nothing if caller wants to re-use the old attname.
     */
    if (attributeName == NULL)
        MemSet(NameStr(att->attname), 0, NAMEDATALEN);
    else if (attributeName != NameStr(att->attname))
        namestrcpy(&(att->attname), attributeName);
 
    att->atttypmod = typmod;
 
    att->attnum = attributeNumber;
    att->attndims = attdim;
 
    att->attnotnull = false;
    att->atthasdef = false;
    att->atthasmissing = false;
    att->attidentity = '\0';
    att->attgenerated = '\0';
    att->attisdropped = false;
    att->attislocal = true;
    att->attinhcount = 0;
    /* variable-length fields are not present in tupledescs */
 
    tuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(oidtypeid));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for type %u", oidtypeid);
    typeForm = (Form_pg_type) GETSTRUCT(tuple);
 
    att->atttypid = oidtypeid;
    att->attlen = typeForm->typlen;
    att->attbyval = typeForm->typbyval;
    att->attalign = typeForm->typalign;
    att->attstorage = typeForm->typstorage;
    att->attcompression = InvalidCompressionMethod;
    att->attcollation = typeForm->typcollation;
 
    populate_compact_attribute(desc, attributeNumber - 1);
 
    ReleaseSysCache(tuple);
}
 
/*
 * TupleDescInitBuiltinEntry
 *      Initialize a tuple descriptor without catalog access.  Only
 *      a limited range of builtin types are supported.
 */
void
TupleDescInitBuiltinEntry(TupleDesc desc,
                          AttrNumber attributeNumber,
                          const char *attributeName,
                          Oid oidtypeid,
                          int32 typmod,
                          int attdim)
{
    Form_pg_attribute att;
 
    /* sanity checks */
    Assert(desc);
    Assert(attributeNumber >= 1);
    Assert(attributeNumber <= desc->natts);
    Assert(attdim >= 0);
    Assert(attdim <= PG_INT16_MAX);
 
    /* initialize the attribute fields */
    att = TupleDescAttr(desc, attributeNumber - 1);
    att->attrelid = 0;          /* dummy value */
 
    /* unlike TupleDescInitEntry, we require an attribute name */
    Assert(attributeName != NULL);
    namestrcpy(&(att->attname), attributeName);
 
    att->atttypmod = typmod;
 
    att->attnum = attributeNumber;
    att->attndims = attdim;
 
    att->attnotnull = false;
    att->atthasdef = false;
    att->atthasmissing = false;
    att->attidentity = '\0';
    att->attgenerated = '\0';
    att->attisdropped = false;
    att->attislocal = true;
    att->attinhcount = 0;
    /* variable-length fields are not present in tupledescs */
 
    att->atttypid = oidtypeid;
 
    /*
     * Our goal here is to support just enough types to let basic builtin
     * commands work without catalog access - e.g. so that we can do certain
     * things even in processes that are not connected to a database.
     */
    switch (oidtypeid)
    {
        case TEXTOID:
        case TEXTARRAYOID:
            att->attlen = -1;
            att->attbyval = false;
            att->attalign = TYPALIGN_INT;
            att->attstorage = TYPSTORAGE_EXTENDED;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = DEFAULT_COLLATION_OID;
            break;
 
        case BOOLOID:
            att->attlen = 1;
            att->attbyval = true;
            att->attalign = TYPALIGN_CHAR;
            att->attstorage = TYPSTORAGE_PLAIN;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = InvalidOid;
            break;
 
        case INT4OID:
            att->attlen = 4;
            att->attbyval = true;
            att->attalign = TYPALIGN_INT;
            att->attstorage = TYPSTORAGE_PLAIN;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = InvalidOid;
            break;
 
        case INT8OID:
            att->attlen = 8;
            att->attbyval = true;
            att->attalign = TYPALIGN_DOUBLE;
            att->attstorage = TYPSTORAGE_PLAIN;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = InvalidOid;
            break;
 
        case OIDOID:
            att->attlen = 4;
            att->attbyval = true;
            att->attalign = TYPALIGN_INT;
            att->attstorage = TYPSTORAGE_PLAIN;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = InvalidOid;
            break;
 
        default:
            elog(ERROR, "unsupported type %u", oidtypeid);
    }
 
    populate_compact_attribute(desc, attributeNumber - 1);
}
 
/*
 * TupleDescInitEntryCollation
 *
 * Assign a nondefault collation to a previously initialized tuple descriptor
 * entry.
 */
void
TupleDescInitEntryCollation(TupleDesc desc,
                            AttrNumber attributeNumber,
                            Oid collationid)
{
    /*
     * sanity checks
     */
    Assert(desc);
    Assert(attributeNumber >= 1);
    Assert(attributeNumber <= desc->natts);
 
    TupleDescAttr(desc, attributeNumber - 1)->attcollation = collationid;
}
 
/*
 * BuildDescFromLists
 *
 * Build a TupleDesc given lists of column names (as String nodes),
 * column type OIDs, typmods, and collation OIDs.
 *
 * No constraints are generated.
 *
 * This is for use with functions returning RECORD.
 */
TupleDesc
BuildDescFromLists(const List *names, const List *types, const List *typmods, const List *collations)
{
    int         natts;
    AttrNumber  attnum;
    ListCell   *l1;
    ListCell   *l2;
    ListCell   *l3;
    ListCell   *l4;
    TupleDesc   desc;
 
    natts = list_length(names);
    Assert(natts == list_length(types));
    Assert(natts == list_length(typmods));
    Assert(natts == list_length(collations));
 
    /*
     * allocate a new tuple descriptor
     */
    desc = CreateTemplateTupleDesc(natts);
 
    attnum = 0;
    forfour(l1, names, l2, types, l3, typmods, l4, collations)
    {
        char       *attname = strVal(lfirst(l1));
        Oid         atttypid = lfirst_oid(l2);
        int32       atttypmod = lfirst_int(l3);
        Oid         attcollation = lfirst_oid(l4);
 
        attnum++;
 
        TupleDescInitEntry(desc, attnum, attname, atttypid, atttypmod, 0);
        TupleDescInitEntryCollation(desc, attnum, attcollation);
    }
 
    return desc;
}
 
/*
 * Get default expression (or NULL if none) for the given attribute number.
 */
Node *
TupleDescGetDefault(TupleDesc tupdesc, AttrNumber attnum)
{
    Node       *result = NULL;
 
    if (tupdesc->constr)
    {
        AttrDefault *attrdef = tupdesc->constr->defval;
 
        for (int i = 0; i < tupdesc->constr->num_defval; i++)
        {
            if (attrdef[i].adnum == attnum)
            {
                result = stringToNode(attrdef[i].adbin);
                break;
            }
        }
    }
 
    return result;
}
 
/* ResourceOwner callbacks */
 
static void
ResOwnerReleaseTupleDesc(Datum res)
{
    TupleDesc   tupdesc = (TupleDesc) DatumGetPointer(res);
 
    /* Like DecrTupleDescRefCount, but don't call ResourceOwnerForget() */
    Assert(tupdesc->tdrefcount > 0);
    if (--tupdesc->tdrefcount == 0)
        FreeTupleDesc(tupdesc);
}
 
static char *
ResOwnerPrintTupleDesc(Datum res)
{
    TupleDesc   tupdesc = (TupleDesc) DatumGetPointer(res);
 
    return psprintf("TupleDesc %p (%u,%d)",
                    tupdesc, tupdesc->tdtypeid, tupdesc->tdtypmod);
}