heaptuple.c

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/*-------------------------------------------------------------------------
 *
 * heaptuple.c
 *    This file contains heap tuple accessor and mutator routines, as well
 *    as various tuple utilities.
 *
 * Some notes about varlenas and this code:
 *
 * Before Postgres 8.3 varlenas always had a 4-byte length header, and
 * therefore always needed 4-byte alignment (at least).  This wasted space
 * for short varlenas, for example CHAR(1) took 5 bytes and could need up to
 * 3 additional padding bytes for alignment.
 *
 * Now, a short varlena (up to 126 data bytes) is reduced to a 1-byte header
 * and we don't align it.  To hide this from datatype-specific functions that
 * don't want to deal with it, such a datum is considered "toasted" and will
 * be expanded back to the normal 4-byte-header format by pg_detoast_datum.
 * (In performance-critical code paths we can use pg_detoast_datum_packed
 * and the appropriate access macros to avoid that overhead.)  Note that this
 * conversion is performed directly in heap_form_tuple, without invoking
 * heaptoast.c.
 *
 * This change will break any code that assumes it needn't detoast values
 * that have been put into a tuple but never sent to disk.  Hopefully there
 * are few such places.
 *
 * Varlenas still have alignment INT (or DOUBLE) in pg_type/pg_attribute, since
 * that's the normal requirement for the untoasted format.  But we ignore that
 * for the 1-byte-header format.  This means that the actual start position
 * of a varlena datum may vary depending on which format it has.  To determine
 * what is stored, we have to require that alignment padding bytes be zero.
 * (Postgres actually has always zeroed them, but now it's required!)  Since
 * the first byte of a 1-byte-header varlena can never be zero, we can examine
 * the first byte after the previous datum to tell if it's a pad byte or the
 * start of a 1-byte-header varlena.
 *
 * Note that while formerly we could rely on the first varlena column of a
 * system catalog to be at the offset suggested by the C struct for the
 * catalog, this is now risky: it's only safe if the preceding field is
 * word-aligned, so that there will never be any padding.
 *
 * We don't pack varlenas whose attstorage is PLAIN, since the data type
 * isn't expecting to have to detoast values.  This is used in particular
 * by oidvector and int2vector, which are used in the system catalogs
 * and we'd like to still refer to them via C struct offsets.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/common/heaptuple.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/heaptoast.h"
#include "access/sysattr.h"
#include "access/tupdesc_details.h"
#include "common/hashfn.h"
#include "utils/datum.h"
#include "utils/expandeddatum.h"
#include "utils/hsearch.h"
#include "utils/memutils.h"
 
 
/*
 * Does att's datatype allow packing into the 1-byte-header varlena format?
 * While functions that use TupleDescAttr() and assign attstorage =
 * TYPSTORAGE_PLAIN cannot use packed varlena headers, functions that call
 * TupleDescInitEntry() use typeForm->typstorage (TYPSTORAGE_EXTENDED) and
 * can use packed varlena headers, e.g.:
 *     CREATE TABLE test(a VARCHAR(10000) STORAGE PLAIN);
 *     INSERT INTO test VALUES (repeat('A',10));
 * This can be verified with pageinspect.
 */
#define ATT_IS_PACKABLE(att) \
    ((att)->attlen == -1 && (att)->attstorage != TYPSTORAGE_PLAIN)
/* Use this if it's already known varlena */
#define VARLENA_ATT_IS_PACKABLE(att) \
    ((att)->attstorage != TYPSTORAGE_PLAIN)
 
/* FormData_pg_attribute.attstorage != TYPSTORAGE_PLAIN and an attlen of -1 */
#define COMPACT_ATTR_IS_PACKABLE(att) \
    ((att)->attlen == -1 && (att)->attispackable)
 
/*
 * Setup for caching pass-by-ref missing attributes in a way that survives
 * tupleDesc destruction.
 */
 
typedef struct
{
    int         len;
    Datum       value;
} missing_cache_key;
 
static HTAB *missing_cache = NULL;
 
static uint32
missing_hash(const void *key, Size keysize)
{
    const missing_cache_key *entry = key;
 
    return hash_bytes((const unsigned char *) DatumGetPointer(entry->value), entry->len);
}
 
static int
missing_match(const void *key1, const void *key2, Size keysize)
{
    const missing_cache_key *entry1 = key1;
    const missing_cache_key *entry2 = key2;
 
    if (entry1->len != entry2->len)
        return entry1->len > entry2->len ? 1 : -1;
 
    return memcmp(DatumGetPointer(entry1->value),
                  DatumGetPointer(entry2->value),
                  entry1->len);
}
 
static void
init_missing_cache(void)
{
    HASHCTL     hash_ctl;
 
    hash_ctl.keysize = sizeof(missing_cache_key);
    hash_ctl.entrysize = sizeof(missing_cache_key);
    hash_ctl.hcxt = TopMemoryContext;
    hash_ctl.hash = missing_hash;
    hash_ctl.match = missing_match;
    missing_cache =
        hash_create("Missing Values Cache",
                    32,
                    &hash_ctl,
                    HASH_ELEM | HASH_CONTEXT | HASH_FUNCTION | HASH_COMPARE);
}
 
/* ----------------------------------------------------------------
 *                      misc support routines
 * ----------------------------------------------------------------
 */
 
/*
 * Return the missing value of an attribute, or NULL if there isn't one.
 */
Datum
getmissingattr(TupleDesc tupleDesc,
               int attnum, bool *isnull)
{
    CompactAttribute *att;
 
    Assert(attnum <= tupleDesc->natts);
    Assert(attnum > 0);
 
    att = TupleDescCompactAttr(tupleDesc, attnum - 1);
 
    if (att->atthasmissing)
    {
        AttrMissing *attrmiss;
 
        Assert(tupleDesc->constr);
        Assert(tupleDesc->constr->missing);
 
        attrmiss = tupleDesc->constr->missing + (attnum - 1);
 
        if (attrmiss->am_present)
        {
            missing_cache_key key;
            missing_cache_key *entry;
            bool        found;
            MemoryContext oldctx;
 
            *isnull = false;
 
            /* no  need to cache by-value attributes */
            if (att->attbyval)
                return attrmiss->am_value;
 
            /* set up cache if required */
            if (missing_cache == NULL)
                init_missing_cache();
 
            /* check if there's a cache entry */
            Assert(att->attlen > 0 || att->attlen == -1);
            if (att->attlen > 0)
                key.len = att->attlen;
            else
                key.len = VARSIZE_ANY(DatumGetPointer(attrmiss->am_value));
            key.value = attrmiss->am_value;
 
            entry = hash_search(missing_cache, &key, HASH_ENTER, &found);
 
            if (!found)
            {
                /* cache miss, so we need a non-transient copy of the datum */
                oldctx = MemoryContextSwitchTo(TopMemoryContext);
                entry->value =
                    datumCopy(attrmiss->am_value, false, att->attlen);
                MemoryContextSwitchTo(oldctx);
            }
 
            return entry->value;
        }
    }
 
    *isnull = true;
    return PointerGetDatum(NULL);
}
 
/*
 * heap_compute_data_size
 *      Determine size of the data area of a tuple to be constructed
 */
Size
heap_compute_data_size(TupleDesc tupleDesc,
                       const Datum *values,
                       const bool *isnull)
{
    Size        data_length = 0;
    int         i;
    int         numberOfAttributes = tupleDesc->natts;
 
    for (i = 0; i < numberOfAttributes; i++)
    {
        Datum       val;
        CompactAttribute *atti;
 
        if (isnull[i])
            continue;
 
        val = values[i];
        atti = TupleDescCompactAttr(tupleDesc, i);
 
        if (COMPACT_ATTR_IS_PACKABLE(atti) &&
            VARATT_CAN_MAKE_SHORT(DatumGetPointer(val)))
        {
            /*
             * we're anticipating converting to a short varlena header, so
             * adjust length and don't count any alignment
             */
            data_length += VARATT_CONVERTED_SHORT_SIZE(DatumGetPointer(val));
        }
        else if (atti->attlen == -1 &&
                 VARATT_IS_EXTERNAL_EXPANDED(DatumGetPointer(val)))
        {
            /*
             * we want to flatten the expanded value so that the constructed
             * tuple doesn't depend on it
             */
            data_length = att_nominal_alignby(data_length, atti->attalignby);
            data_length += EOH_get_flat_size(DatumGetEOHP(val));
        }
        else
        {
            data_length = att_datum_alignby(data_length, atti->attalignby,
                                            atti->attlen, val);
            data_length = att_addlength_datum(data_length, atti->attlen,
                                              val);
        }
    }
 
    return data_length;
}
 
/*
 * Per-attribute helper for heap_fill_tuple and other routines building tuples.
 *
 * Fill in either a data value or a bit in the null bitmask
 */
static inline void
fill_val(CompactAttribute *att,
         bits8 **bit,
         int *bitmask,
         char **dataP,
         uint16 *infomask,
         Datum datum,
         bool isnull)
{
    Size        data_length;
    char       *data = *dataP;
 
    /*
     * If we're building a null bitmap, set the appropriate bit for the
     * current column value here.
     */
    if (bit != NULL)
    {
        if (*bitmask != HIGHBIT)
            *bitmask <<= 1;
        else
        {
            *bit += 1;
            **bit = 0x0;
            *bitmask = 1;
        }
 
        if (isnull)
        {
            *infomask |= HEAP_HASNULL;
            return;
        }
 
        **bit |= *bitmask;
    }
 
    /*
     * XXX we use the att_nominal_alignby macro on the pointer value itself,
     * not on an offset.  This is a bit of a hack.
     */
    if (att->attbyval)
    {
        /* pass-by-value */
        data = (char *) att_nominal_alignby(data, att->attalignby);
        store_att_byval(data, datum, att->attlen);
        data_length = att->attlen;
    }
    else if (att->attlen == -1)
    {
        /* varlena */
        Pointer     val = DatumGetPointer(datum);
 
        *infomask |= HEAP_HASVARWIDTH;
        if (VARATT_IS_EXTERNAL(val))
        {
            if (VARATT_IS_EXTERNAL_EXPANDED(val))
            {
                /*
                 * we want to flatten the expanded value so that the
                 * constructed tuple doesn't depend on it
                 */
                ExpandedObjectHeader *eoh = DatumGetEOHP(datum);
 
                data = (char *) att_nominal_alignby(data, att->attalignby);
                data_length = EOH_get_flat_size(eoh);
                EOH_flatten_into(eoh, data, data_length);
            }
            else
            {
                *infomask |= HEAP_HASEXTERNAL;
                /* no alignment, since it's short by definition */
                data_length = VARSIZE_EXTERNAL(val);
                memcpy(data, val, data_length);
            }
        }
        else if (VARATT_IS_SHORT(val))
        {
            /* no alignment for short varlenas */
            data_length = VARSIZE_SHORT(val);
            memcpy(data, val, data_length);
        }
        else if (att->attispackable && VARATT_CAN_MAKE_SHORT(val))
        {
            /* convert to short varlena -- no alignment */
            data_length = VARATT_CONVERTED_SHORT_SIZE(val);
            SET_VARSIZE_SHORT(data, data_length);
            memcpy(data + 1, VARDATA(val), data_length - 1);
        }
        else
        {
            /* full 4-byte header varlena */
            data = (char *) att_nominal_alignby(data, att->attalignby);
            data_length = VARSIZE(val);
            memcpy(data, val, data_length);
        }
    }
    else if (att->attlen == -2)
    {
        /* cstring ... never needs alignment */
        *infomask |= HEAP_HASVARWIDTH;
        Assert(att->attalignby == sizeof(char));
        data_length = strlen(DatumGetCString(datum)) + 1;
        memcpy(data, DatumGetPointer(datum), data_length);
    }
    else
    {
        /* fixed-length pass-by-reference */
        data = (char *) att_nominal_alignby(data, att->attalignby);
        Assert(att->attlen > 0);
        data_length = att->attlen;
        memcpy(data, DatumGetPointer(datum), data_length);
    }
 
    data += data_length;
    *dataP = data;
}
 
/*
 * heap_fill_tuple
 *      Load data portion of a tuple from values/isnull arrays
 *
 * We also fill the null bitmap (if any) and set the infomask bits
 * that reflect the tuple's data contents.
 *
 * NOTE: it is now REQUIRED that the caller have pre-zeroed the data area.
 */
void
heap_fill_tuple(TupleDesc tupleDesc,
                const Datum *values, const bool *isnull,
                char *data, Size data_size,
                uint16 *infomask, bits8 *bit)
{
    bits8      *bitP;
    int         bitmask;
    int         i;
    int         numberOfAttributes = tupleDesc->natts;
 
#ifdef USE_ASSERT_CHECKING
    char       *start = data;
#endif
 
    if (bit != NULL)
    {
        bitP = &bit[-1];
        bitmask = HIGHBIT;
    }
    else
    {
        /* just to keep compiler quiet */
        bitP = NULL;
        bitmask = 0;
    }
 
    *infomask &= ~(HEAP_HASNULL | HEAP_HASVARWIDTH | HEAP_HASEXTERNAL);
 
    for (i = 0; i < numberOfAttributes; i++)
    {
        CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, i);
 
        fill_val(attr,
                 bitP ? &bitP : NULL,
                 &bitmask,
                 &data,
                 infomask,
                 values ? values[i] : PointerGetDatum(NULL),
                 isnull ? isnull[i] : true);
    }
 
    Assert((data - start) == data_size);
}
 
 
/* ----------------------------------------------------------------
 *                      heap tuple interface
 * ----------------------------------------------------------------
 */
 
/* ----------------
 *      heap_attisnull  - returns true iff tuple attribute is not present
 * ----------------
 */
bool
heap_attisnull(HeapTuple tup, int attnum, TupleDesc tupleDesc)
{
    /*
     * We allow a NULL tupledesc for relations not expected to have missing
     * values, such as catalog relations and indexes.
     */
    Assert(!tupleDesc || attnum <= tupleDesc->natts);
    if (attnum > (int) HeapTupleHeaderGetNatts(tup->t_data))
    {
        if (tupleDesc &&
            TupleDescCompactAttr(tupleDesc, attnum - 1)->atthasmissing)
            return false;
        else
            return true;
    }
 
    if (attnum > 0)
    {
        if (HeapTupleNoNulls(tup))
            return false;
        return att_isnull(attnum - 1, tup->t_data->t_bits);
    }
 
    switch (attnum)
    {
        case TableOidAttributeNumber:
        case SelfItemPointerAttributeNumber:
        case MinTransactionIdAttributeNumber:
        case MinCommandIdAttributeNumber:
        case MaxTransactionIdAttributeNumber:
        case MaxCommandIdAttributeNumber:
            /* these are never null */
            break;
 
        default:
            elog(ERROR, "invalid attnum: %d", attnum);
    }
 
    return false;
}
 
/* ----------------
 *      nocachegetattr
 *
 *      This only gets called from fastgetattr(), in cases where we
 *      can't use the attcacheoff and the value is not null.
 *
 *      NOTE: if you need to change this code, see also heap_deform_tuple.
 *      Also see nocache_index_getattr, which is the same code for index
 *      tuples.
 * ----------------
 */
Datum
nocachegetattr(HeapTuple tup,
               int attnum,
               TupleDesc tupleDesc)
{
    CompactAttribute *cattr;
    HeapTupleHeader td = tup->t_data;
    char       *tp;             /* ptr to data part of tuple */
    bits8      *bp = td->t_bits;    /* ptr to null bitmap in tuple */
    int         off;            /* current offset within data */
    int         startAttr;
    int         firstNullAttr;
    int         i;
    bool        hasnulls = HeapTupleHasNulls(tup);
 
    /* Did someone forget to call TupleDescFinalize()? */
    Assert(tupleDesc->firstNonCachedOffsetAttr >= 0);
 
    attnum--;
 
    /*
     * To minimize the number of attributes we need to look at, start walking
     * the tuple at the attribute with the highest attcacheoff prior to attnum
     * or the first NULL attribute prior to attnum, whichever comes first.
     */
    if (hasnulls)
        firstNullAttr = first_null_attr(bp, attnum);
    else
        firstNullAttr = attnum;
 
    if (tupleDesc->firstNonCachedOffsetAttr > 0 && firstNullAttr > 0)
    {
        /*
         * Try to start with the highest attribute with an attcacheoff that's
         * prior to the one we're looking for, or with the attribute prior to
         * the first NULL attribute, if there is one.
         */
        startAttr = Min(tupleDesc->firstNonCachedOffsetAttr - 1, firstNullAttr - 1);
        off = TupleDescCompactAttr(tupleDesc, startAttr)->attcacheoff;
    }
    else
    {
        /* Otherwise, start at the beginning... */
        startAttr = 0;
        off = 0;
    }
 
    tp = (char *) td + td->t_hoff;
 
    /*
     * Calculate 'off' up to the first NULL attr.  We use two cheaper loops
     * when the tuple has no variable-width columns.  When variable-width
     * columns exists, we use att_addlength_pointer() to move the offset
     * beyond the current attribute.
     */
    if (!HeapTupleHasVarWidth(tup))
    {
        for (i = startAttr; i < firstNullAttr; i++)
        {
            cattr = TupleDescCompactAttr(tupleDesc, i);
 
            off = att_nominal_alignby(off, cattr->attalignby);
            off += cattr->attlen;
        }
 
        for (; i < attnum; i++)
        {
            if (att_isnull(i, bp))
                continue;
 
            cattr = TupleDescCompactAttr(tupleDesc, i);
 
            off = att_nominal_alignby(off, cattr->attalignby);
            off += cattr->attlen;
        }
    }
    else
    {
        for (i = startAttr; i < firstNullAttr; i++)
        {
            int         attlen;
 
            cattr = TupleDescCompactAttr(tupleDesc, i);
            attlen = cattr->attlen;
 
            /*
             * cstrings don't exist in heap tuples.  Use pg_assume to instruct
             * the compiler not to emit the cstring-related code in
             * att_addlength_pointer().
             */
            pg_assume(attlen > 0 || attlen == -1);
 
            off = att_pointer_alignby(off,
                                      cattr->attalignby,
                                      attlen,
                                      tp + off);
            off = att_addlength_pointer(off, attlen, tp + off);
        }
 
        for (; i < attnum; i++)
        {
            int         attlen;
 
            if (att_isnull(i, bp))
                continue;
 
            cattr = TupleDescCompactAttr(tupleDesc, i);
            attlen = cattr->attlen;
 
            /* As above, heaptuples have no cstrings */
            pg_assume(attlen > 0 || attlen == -1);
 
            off = att_pointer_alignby(off, cattr->attalignby, attlen,
                                      tp + off);
            off = att_addlength_pointer(off, attlen, tp + off);
        }
    }
 
    cattr = TupleDescCompactAttr(tupleDesc, attnum);
    off = att_pointer_alignby(off,
                              cattr->attalignby,
                              cattr->attlen,
                              tp + off);
 
    return fetchatt(cattr, tp + off);
}
 
/* ----------------
 *      heap_getsysattr
 *
 *      Fetch the value of a system attribute for a tuple.
 *
 * This is a support routine for heap_getattr().  The function has already
 * determined that the attnum refers to a system attribute.
 * ----------------
 */
Datum
heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc, bool *isnull)
{
    Datum       result;
 
    Assert(tup);
 
    /* Currently, no sys attribute ever reads as NULL. */
    *isnull = false;
 
    switch (attnum)
    {
        case SelfItemPointerAttributeNumber:
            /* pass-by-reference datatype */
            result = PointerGetDatum(&(tup->t_self));
            break;
        case MinTransactionIdAttributeNumber:
            result = TransactionIdGetDatum(HeapTupleHeaderGetRawXmin(tup->t_data));
            break;
        case MaxTransactionIdAttributeNumber:
            result = TransactionIdGetDatum(HeapTupleHeaderGetRawXmax(tup->t_data));
            break;
        case MinCommandIdAttributeNumber:
        case MaxCommandIdAttributeNumber:
 
            /*
             * cmin and cmax are now both aliases for the same field, which
             * can in fact also be a combo command id.  XXX perhaps we should
             * return the "real" cmin or cmax if possible, that is if we are
             * inside the originating transaction?
             */
            result = CommandIdGetDatum(HeapTupleHeaderGetRawCommandId(tup->t_data));
            break;
        case TableOidAttributeNumber:
            result = ObjectIdGetDatum(tup->t_tableOid);
            break;
        default:
            elog(ERROR, "invalid attnum: %d", attnum);
            result = 0;         /* keep compiler quiet */
            break;
    }
    return result;
}
 
/* ----------------
 *      heap_copytuple
 *
 *      returns a copy of an entire tuple
 *
 * The HeapTuple struct, tuple header, and tuple data are all allocated
 * as a single palloc() block.
 * ----------------
 */
HeapTuple
heap_copytuple(HeapTuple tuple)
{
    HeapTuple   newTuple;
 
    if (!HeapTupleIsValid(tuple) || tuple->t_data == NULL)
        return NULL;
 
    newTuple = (HeapTuple) palloc(HEAPTUPLESIZE + tuple->t_len);
    newTuple->t_len = tuple->t_len;
    newTuple->t_self = tuple->t_self;
    newTuple->t_tableOid = tuple->t_tableOid;
    newTuple->t_data = (HeapTupleHeader) ((char *) newTuple + HEAPTUPLESIZE);
    memcpy(newTuple->t_data, tuple->t_data, tuple->t_len);
    return newTuple;
}
 
/* ----------------
 *      heap_copytuple_with_tuple
 *
 *      copy a tuple into a caller-supplied HeapTuple management struct
 *
 * Note that after calling this function, the "dest" HeapTuple will not be
 * allocated as a single palloc() block (unlike with heap_copytuple()).
 * ----------------
 */
void
heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest)
{
    if (!HeapTupleIsValid(src) || src->t_data == NULL)
    {
        dest->t_data = NULL;
        return;
    }
 
    dest->t_len = src->t_len;
    dest->t_self = src->t_self;
    dest->t_tableOid = src->t_tableOid;
    dest->t_data = (HeapTupleHeader) palloc(src->t_len);
    memcpy(dest->t_data, src->t_data, src->t_len);
}
 
/*
 * Expand a tuple which has fewer attributes than required. For each attribute
 * not present in the sourceTuple, if there is a missing value that will be
 * used. Otherwise the attribute will be set to NULL.
 *
 * The source tuple must have fewer attributes than the required number.
 *
 * Only one of targetHeapTuple and targetMinimalTuple may be supplied. The
 * other argument must be NULL.
 */
static void
expand_tuple(HeapTuple *targetHeapTuple,
             MinimalTuple *targetMinimalTuple,
             HeapTuple sourceTuple,
             TupleDesc tupleDesc)
{
    AttrMissing *attrmiss = NULL;
    int         attnum;
    int         firstmissingnum;
    bool        hasNulls = HeapTupleHasNulls(sourceTuple);
    HeapTupleHeader targetTHeader;
    HeapTupleHeader sourceTHeader = sourceTuple->t_data;
    int         sourceNatts = HeapTupleHeaderGetNatts(sourceTHeader);
    int         natts = tupleDesc->natts;
    int         sourceNullLen;
    int         targetNullLen;
    Size        sourceDataLen = sourceTuple->t_len - sourceTHeader->t_hoff;
    Size        targetDataLen;
    Size        len;
    int         hoff;
    bits8      *nullBits = NULL;
    int         bitMask = 0;
    char       *targetData;
    uint16     *infoMask;
 
    Assert((targetHeapTuple && !targetMinimalTuple)
           || (!targetHeapTuple && targetMinimalTuple));
 
    Assert(sourceNatts < natts);
 
    sourceNullLen = (hasNulls ? BITMAPLEN(sourceNatts) : 0);
 
    targetDataLen = sourceDataLen;
 
    if (tupleDesc->constr &&
        tupleDesc->constr->missing)
    {
        /*
         * If there are missing values we want to put them into the tuple.
         * Before that we have to compute the extra length for the values
         * array and the variable length data.
         */
        attrmiss = tupleDesc->constr->missing;
 
        /*
         * Find the first item in attrmiss for which we don't have a value in
         * the source. We can ignore all the missing entries before that.
         */
        for (firstmissingnum = sourceNatts;
             firstmissingnum < natts;
             firstmissingnum++)
        {
            if (attrmiss[firstmissingnum].am_present)
                break;
            else
                hasNulls = true;
        }
 
        /*
         * Now walk the missing attributes. If there is a missing value make
         * space for it. Otherwise, it's going to be NULL.
         */
        for (attnum = firstmissingnum;
             attnum < natts;
             attnum++)
        {
            if (attrmiss[attnum].am_present)
            {
                CompactAttribute *att = TupleDescCompactAttr(tupleDesc, attnum);
 
                targetDataLen = att_datum_alignby(targetDataLen,
                                                  att->attalignby,
                                                  att->attlen,
                                                  attrmiss[attnum].am_value);
 
                targetDataLen = att_addlength_datum(targetDataLen,
                                                    att->attlen,
                                                    attrmiss[attnum].am_value);
            }
            else
            {
                /* no missing value, so it must be null */
                hasNulls = true;
            }
        }
    }                           /* end if have missing values */
    else
    {
        /*
         * If there are no missing values at all then NULLS must be allowed,
         * since some of the attributes are known to be absent.
         */
        hasNulls = true;
    }
 
    len = 0;
 
    if (hasNulls)
    {
        targetNullLen = BITMAPLEN(natts);
        len += targetNullLen;
    }
    else
        targetNullLen = 0;
 
    /*
     * Allocate and zero the space needed.  Note that the tuple body and
     * HeapTupleData management structure are allocated in one chunk.
     */
    if (targetHeapTuple)
    {
        len += offsetof(HeapTupleHeaderData, t_bits);
        hoff = len = MAXALIGN(len); /* align user data safely */
        len += targetDataLen;
 
        *targetHeapTuple = (HeapTuple) palloc0(HEAPTUPLESIZE + len);
        (*targetHeapTuple)->t_data
            = targetTHeader
            = (HeapTupleHeader) ((char *) *targetHeapTuple + HEAPTUPLESIZE);
        (*targetHeapTuple)->t_len = len;
        (*targetHeapTuple)->t_tableOid = sourceTuple->t_tableOid;
        (*targetHeapTuple)->t_self = sourceTuple->t_self;
 
        targetTHeader->t_infomask = sourceTHeader->t_infomask;
        targetTHeader->t_hoff = hoff;
        HeapTupleHeaderSetNatts(targetTHeader, natts);
        HeapTupleHeaderSetDatumLength(targetTHeader, len);
        HeapTupleHeaderSetTypeId(targetTHeader, tupleDesc->tdtypeid);
        HeapTupleHeaderSetTypMod(targetTHeader, tupleDesc->tdtypmod);
        /* We also make sure that t_ctid is invalid unless explicitly set */
        ItemPointerSetInvalid(&(targetTHeader->t_ctid));
        if (targetNullLen > 0)
            nullBits = (bits8 *) ((char *) (*targetHeapTuple)->t_data
                                  + offsetof(HeapTupleHeaderData, t_bits));
        targetData = (char *) (*targetHeapTuple)->t_data + hoff;
        infoMask = &(targetTHeader->t_infomask);
    }
    else
    {
        len += SizeofMinimalTupleHeader;
        hoff = len = MAXALIGN(len); /* align user data safely */
        len += targetDataLen;
 
        *targetMinimalTuple = (MinimalTuple) palloc0(len);
        (*targetMinimalTuple)->t_len = len;
        (*targetMinimalTuple)->t_hoff = hoff + MINIMAL_TUPLE_OFFSET;
        (*targetMinimalTuple)->t_infomask = sourceTHeader->t_infomask;
        /* Same macro works for MinimalTuples */
        HeapTupleHeaderSetNatts(*targetMinimalTuple, natts);
        if (targetNullLen > 0)
            nullBits = (bits8 *) ((char *) *targetMinimalTuple
                                  + offsetof(MinimalTupleData, t_bits));
        targetData = (char *) *targetMinimalTuple + hoff;
        infoMask = &((*targetMinimalTuple)->t_infomask);
    }
 
    if (targetNullLen > 0)
    {
        if (sourceNullLen > 0)
        {
            /* if bitmap pre-existed copy in - all is set */
            memcpy(nullBits,
                   ((char *) sourceTHeader)
                   + offsetof(HeapTupleHeaderData, t_bits),
                   sourceNullLen);
            nullBits += sourceNullLen - 1;
        }
        else
        {
            sourceNullLen = BITMAPLEN(sourceNatts);
            /* Set NOT NULL for all existing attributes */
            memset(nullBits, 0xff, sourceNullLen);
 
            nullBits += sourceNullLen - 1;
 
            if (sourceNatts & 0x07)
            {
                /* build the mask (inverted!) */
                bitMask = 0xff << (sourceNatts & 0x07);
                /* Voila */
                *nullBits = ~bitMask;
            }
        }
 
        bitMask = (1 << ((sourceNatts - 1) & 0x07));
    }                           /* End if have null bitmap */
 
    memcpy(targetData,
           ((char *) sourceTuple->t_data) + sourceTHeader->t_hoff,
           sourceDataLen);
 
    targetData += sourceDataLen;
 
    /* Now fill in the missing values */
    for (attnum = sourceNatts; attnum < natts; attnum++)
    {
        CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, attnum);
 
        if (attrmiss && attrmiss[attnum].am_present)
        {
            fill_val(attr,
                     nullBits ? &nullBits : NULL,
                     &bitMask,
                     &targetData,
                     infoMask,
                     attrmiss[attnum].am_value,
                     false);
        }
        else
        {
            fill_val(attr,
                     &nullBits,
                     &bitMask,
                     &targetData,
                     infoMask,
                     (Datum) 0,
                     true);
        }
    }                           /* end loop over missing attributes */
}
 
/*
 * Fill in the missing values for a minimal HeapTuple
 */
MinimalTuple
minimal_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc)
{
    MinimalTuple minimalTuple;
 
    expand_tuple(NULL, &minimalTuple, sourceTuple, tupleDesc);
    return minimalTuple;
}
 
/*
 * Fill in the missing values for an ordinary HeapTuple
 */
HeapTuple
heap_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc)
{
    HeapTuple   heapTuple;
 
    expand_tuple(&heapTuple, NULL, sourceTuple, tupleDesc);
    return heapTuple;
}
 
/* ----------------
 *      heap_copy_tuple_as_datum
 *
 *      copy a tuple as a composite-type Datum
 * ----------------
 */
Datum
heap_copy_tuple_as_datum(HeapTuple tuple, TupleDesc tupleDesc)
{
    HeapTupleHeader td;
 
    /*
     * If the tuple contains any external TOAST pointers, we have to inline
     * those fields to meet the conventions for composite-type Datums.
     */
    if (HeapTupleHasExternal(tuple))
        return toast_flatten_tuple_to_datum(tuple->t_data,
                                            tuple->t_len,
                                            tupleDesc);
 
    /*
     * Fast path for easy case: just make a palloc'd copy and insert the
     * correct composite-Datum header fields (since those may not be set if
     * the given tuple came from disk, rather than from heap_form_tuple).
     */
    td = (HeapTupleHeader) palloc(tuple->t_len);
    memcpy(td, tuple->t_data, tuple->t_len);
 
    HeapTupleHeaderSetDatumLength(td, tuple->t_len);
    HeapTupleHeaderSetTypeId(td, tupleDesc->tdtypeid);
    HeapTupleHeaderSetTypMod(td, tupleDesc->tdtypmod);
 
    return PointerGetDatum(td);
}
 
/*
 * heap_form_tuple
 *      construct a tuple from the given values[] and isnull[] arrays,
 *      which are of the length indicated by tupleDescriptor->natts
 *
 * The result is allocated in the current memory context.
 */
HeapTuple
heap_form_tuple(TupleDesc tupleDescriptor,
                const Datum *values,
                const bool *isnull)
{
    HeapTuple   tuple;          /* return tuple */
    HeapTupleHeader td;         /* tuple data */
    Size        len,
                data_len;
    int         hoff;
    bool        hasnull = false;
    int         numberOfAttributes = tupleDescriptor->natts;
    int         i;
 
    if (numberOfAttributes > MaxTupleAttributeNumber)
        ereport(ERROR,
                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                 errmsg("number of columns (%d) exceeds limit (%d)",
                        numberOfAttributes, MaxTupleAttributeNumber)));
 
    /*
     * Check for nulls
     */
    for (i = 0; i < numberOfAttributes; i++)
    {
        if (isnull[i])
        {
            hasnull = true;
            break;
        }
    }
 
    /*
     * Determine total space needed
     */
    len = offsetof(HeapTupleHeaderData, t_bits);
 
    if (hasnull)
        len += BITMAPLEN(numberOfAttributes);
 
    hoff = len = MAXALIGN(len); /* align user data safely */
 
    data_len = heap_compute_data_size(tupleDescriptor, values, isnull);
 
    len += data_len;
 
    /*
     * Allocate and zero the space needed.  Note that the tuple body and
     * HeapTupleData management structure are allocated in one chunk.
     */
    tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + len);
    tuple->t_data = td = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);
 
    /*
     * And fill in the information.  Note we fill the Datum fields even though
     * this tuple may never become a Datum.  This lets HeapTupleHeaderGetDatum
     * identify the tuple type if needed.
     */
    tuple->t_len = len;
    ItemPointerSetInvalid(&(tuple->t_self));
    tuple->t_tableOid = InvalidOid;
 
    HeapTupleHeaderSetDatumLength(td, len);
    HeapTupleHeaderSetTypeId(td, tupleDescriptor->tdtypeid);
    HeapTupleHeaderSetTypMod(td, tupleDescriptor->tdtypmod);
    /* We also make sure that t_ctid is invalid unless explicitly set */
    ItemPointerSetInvalid(&(td->t_ctid));
 
    HeapTupleHeaderSetNatts(td, numberOfAttributes);
    td->t_hoff = hoff;
 
    heap_fill_tuple(tupleDescriptor,
                    values,
                    isnull,
                    (char *) td + hoff,
                    data_len,
                    &td->t_infomask,
                    (hasnull ? td->t_bits : NULL));
 
    return tuple;
}
 
/*
 * heap_modify_tuple
 *      form a new tuple from an old tuple and a set of replacement values.
 *
 * The replValues, replIsnull, and doReplace arrays must be of the length
 * indicated by tupleDesc->natts.  The new tuple is constructed using the data
 * from replValues/replIsnull at columns where doReplace is true, and using
 * the data from the old tuple at columns where doReplace is false.
 *
 * The result is allocated in the current memory context.
 */
HeapTuple
heap_modify_tuple(HeapTuple tuple,
                  TupleDesc tupleDesc,
                  const Datum *replValues,
                  const bool *replIsnull,
                  const bool *doReplace)
{
    int         numberOfAttributes = tupleDesc->natts;
    int         attoff;
    Datum      *values;
    bool       *isnull;
    HeapTuple   newTuple;
 
    /*
     * allocate and fill values and isnull arrays from either the tuple or the
     * repl information, as appropriate.
     *
     * NOTE: it's debatable whether to use heap_deform_tuple() here or just
     * heap_getattr() only the non-replaced columns.  The latter could win if
     * there are many replaced columns and few non-replaced ones. However,
     * heap_deform_tuple costs only O(N) while the heap_getattr way would cost
     * O(N^2) if there are many non-replaced columns, so it seems better to
     * err on the side of linear cost.
     */
    values = palloc_array(Datum, numberOfAttributes);
    isnull = palloc_array(bool, numberOfAttributes);
 
    heap_deform_tuple(tuple, tupleDesc, values, isnull);
 
    for (attoff = 0; attoff < numberOfAttributes; attoff++)
    {
        if (doReplace[attoff])
        {
            values[attoff] = replValues[attoff];
            isnull[attoff] = replIsnull[attoff];
        }
    }
 
    /*
     * create a new tuple from the values and isnull arrays
     */
    newTuple = heap_form_tuple(tupleDesc, values, isnull);
 
    pfree(values);
    pfree(isnull);
 
    /*
     * copy the identification info of the old tuple: t_ctid, t_self
     */
    newTuple->t_data->t_ctid = tuple->t_data->t_ctid;
    newTuple->t_self = tuple->t_self;
    newTuple->t_tableOid = tuple->t_tableOid;
 
    return newTuple;
}
 
/*
 * heap_modify_tuple_by_cols
 *      form a new tuple from an old tuple and a set of replacement values.
 *
 * This is like heap_modify_tuple, except that instead of specifying which
 * column(s) to replace by a boolean map, an array of target column numbers
 * is used.  This is often more convenient when a fixed number of columns
 * are to be replaced.  The replCols, replValues, and replIsnull arrays must
 * be of length nCols.  Target column numbers are indexed from 1.
 *
 * The result is allocated in the current memory context.
 */
HeapTuple
heap_modify_tuple_by_cols(HeapTuple tuple,
                          TupleDesc tupleDesc,
                          int nCols,
                          const int *replCols,
                          const Datum *replValues,
                          const bool *replIsnull)
{
    int         numberOfAttributes = tupleDesc->natts;
    Datum      *values;
    bool       *isnull;
    HeapTuple   newTuple;
    int         i;
 
    /*
     * allocate and fill values and isnull arrays from the tuple, then replace
     * selected columns from the input arrays.
     */
    values = palloc_array(Datum, numberOfAttributes);
    isnull = palloc_array(bool, numberOfAttributes);
 
    heap_deform_tuple(tuple, tupleDesc, values, isnull);
 
    for (i = 0; i < nCols; i++)
    {
        int         attnum = replCols[i];
 
        if (attnum <= 0 || attnum > numberOfAttributes)
            elog(ERROR, "invalid column number %d", attnum);
        values[attnum - 1] = replValues[i];
        isnull[attnum - 1] = replIsnull[i];
    }
 
    /*
     * create a new tuple from the values and isnull arrays
     */
    newTuple = heap_form_tuple(tupleDesc, values, isnull);
 
    pfree(values);
    pfree(isnull);
 
    /*
     * copy the identification info of the old tuple: t_ctid, t_self
     */
    newTuple->t_data->t_ctid = tuple->t_data->t_ctid;
    newTuple->t_self = tuple->t_self;
    newTuple->t_tableOid = tuple->t_tableOid;
 
    return newTuple;
}
 
/*
 * heap_deform_tuple
 *      Given a tuple, extract data into values/isnull arrays; this is
 *      the inverse of heap_form_tuple.
 *
 *      Storage for the values/isnull arrays is provided by the caller;
 *      it should be sized according to tupleDesc->natts not
 *      HeapTupleHeaderGetNatts(tuple->t_data).
 *
 *      Note that for pass-by-reference datatypes, the pointer placed
 *      in the Datum will point into the given tuple.
 *
 *      When all or most of a tuple's fields need to be extracted,
 *      this routine will be significantly quicker than a loop around
 *      heap_getattr; the loop will become O(N^2) as soon as any
 *      noncacheable attribute offsets are involved.
 */
void
heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
                  Datum *values, bool *isnull)
{
    HeapTupleHeader tup = tuple->t_data;
    CompactAttribute *cattr;
    bool        hasnulls = HeapTupleHasNulls(tuple);
    int         tdesc_natts = tupleDesc->natts;
    int         natts;          /* number of atts to extract */
    int         attnum;
    char       *tp;             /* ptr to tuple data */
    uint32      off;            /* offset in tuple data */
    bits8      *bp = tup->t_bits;   /* ptr to null bitmap in tuple */
    int         firstNonCacheOffsetAttr;
    int         firstNullAttr;
 
    natts = HeapTupleHeaderGetNatts(tup);
 
    /* Did someone forget to call TupleDescFinalize()? */
    Assert(tupleDesc->firstNonCachedOffsetAttr >= 0);
 
    /*
     * In inheritance situations, it is possible that the given tuple actually
     * has more fields than the caller is expecting.  Don't run off the end of
     * the caller's arrays.
     */
    natts = Min(natts, tdesc_natts);
    firstNonCacheOffsetAttr = Min(tupleDesc->firstNonCachedOffsetAttr, natts);
 
    if (hasnulls)
    {
        firstNullAttr = first_null_attr(bp, natts);
 
        /*
         * XXX: it'd be nice to use populate_isnull_array() here, but that
         * requires that the isnull array's size is rounded up to the next
         * multiple of 8.  Doing that would require adjusting many locations
         * that allocate the array.
         */
        firstNonCacheOffsetAttr = Min(firstNonCacheOffsetAttr, firstNullAttr);
    }
    else
        firstNullAttr = natts;
 
    tp = (char *) tup + tup->t_hoff;
    attnum = 0;
 
    if (firstNonCacheOffsetAttr > 0)
    {
#ifdef USE_ASSERT_CHECKING
        /* In Assert enabled builds, verify attcacheoff is correct */
        int         offcheck = 0;
#endif
        do
        {
            isnull[attnum] = false;
            cattr = TupleDescCompactAttr(tupleDesc, attnum);
            off = cattr->attcacheoff;
 
#ifdef USE_ASSERT_CHECKING
            offcheck = att_nominal_alignby(offcheck, cattr->attalignby);
            Assert(offcheck == cattr->attcacheoff);
            offcheck += cattr->attlen;
#endif
 
            values[attnum] = fetch_att_noerr(tp + off,
                                             cattr->attbyval,
                                             cattr->attlen);
        } while (++attnum < firstNonCacheOffsetAttr);
        off += cattr->attlen;
    }
    else
        off = 0;
 
    for (; attnum < firstNullAttr; attnum++)
    {
        isnull[attnum] = false;
        cattr = TupleDescCompactAttr(tupleDesc, attnum);
        values[attnum] = align_fetch_then_add(tp,
                                              &off,
                                              cattr->attbyval,
                                              cattr->attlen,
                                              cattr->attalignby);
    }
 
    for (; attnum < natts; attnum++)
    {
        Assert(hasnulls);
 
        if (att_isnull(attnum, bp))
        {
            values[attnum] = (Datum) 0;
            isnull[attnum] = true;
            continue;
        }
 
        isnull[attnum] = false;
        cattr = TupleDescCompactAttr(tupleDesc, attnum);
 
        /* align 'off', fetch the attr's value, and increment off beyond it */
        values[attnum] = align_fetch_then_add(tp,
                                              &off,
                                              cattr->attbyval,
                                              cattr->attlen,
                                              cattr->attalignby);
    }
 
    /*
     * If tuple doesn't have all the atts indicated by tupleDesc, read the
     * rest as nulls or missing values as appropriate.
     */
    for (; attnum < tdesc_natts; attnum++)
        values[attnum] = getmissingattr(tupleDesc, attnum + 1, &isnull[attnum]);
}
 
/*
 * heap_freetuple
 */
void
heap_freetuple(HeapTuple htup)
{
    pfree(htup);
}
 
 
/*
 * heap_form_minimal_tuple
 *      construct a MinimalTuple from the given values[] and isnull[] arrays,
 *      which are of the length indicated by tupleDescriptor->natts
 *
 * This is exactly like heap_form_tuple() except that the result is a
 * "minimal" tuple lacking a HeapTupleData header as well as room for system
 * columns.
 *
 * The result is allocated in the current memory context.
 */
MinimalTuple
heap_form_minimal_tuple(TupleDesc tupleDescriptor,
                        const Datum *values,
                        const bool *isnull,
                        Size extra)
{
    MinimalTuple tuple;         /* return tuple */
    char       *mem;
    Size        len,
                data_len;
    int         hoff;
    bool        hasnull = false;
    int         numberOfAttributes = tupleDescriptor->natts;
    int         i;
 
    Assert(extra == MAXALIGN(extra));
 
    if (numberOfAttributes > MaxTupleAttributeNumber)
        ereport(ERROR,
                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                 errmsg("number of columns (%d) exceeds limit (%d)",
                        numberOfAttributes, MaxTupleAttributeNumber)));
 
    /*
     * Check for nulls
     */
    for (i = 0; i < numberOfAttributes; i++)
    {
        if (isnull[i])
        {
            hasnull = true;
            break;
        }
    }
 
    /*
     * Determine total space needed
     */
    len = SizeofMinimalTupleHeader;
 
    if (hasnull)
        len += BITMAPLEN(numberOfAttributes);
 
    hoff = len = MAXALIGN(len); /* align user data safely */
 
    data_len = heap_compute_data_size(tupleDescriptor, values, isnull);
 
    len += data_len;
 
    /*
     * Allocate and zero the space needed.
     */
    mem = palloc0(len + extra);
    tuple = (MinimalTuple) (mem + extra);
 
    /*
     * And fill in the information.
     */
    tuple->t_len = len;
    HeapTupleHeaderSetNatts(tuple, numberOfAttributes);
    tuple->t_hoff = hoff + MINIMAL_TUPLE_OFFSET;
 
    heap_fill_tuple(tupleDescriptor,
                    values,
                    isnull,
                    (char *) tuple + hoff,
                    data_len,
                    &tuple->t_infomask,
                    (hasnull ? tuple->t_bits : NULL));
 
    return tuple;
}
 
/*
 * heap_free_minimal_tuple
 */
void
heap_free_minimal_tuple(MinimalTuple mtup)
{
    pfree(mtup);
}
 
/*
 * heap_copy_minimal_tuple
 *      copy a MinimalTuple
 *
 * The result is allocated in the current memory context.
 */
MinimalTuple
heap_copy_minimal_tuple(MinimalTuple mtup, Size extra)
{
    MinimalTuple result;
    char       *mem;
 
    Assert(extra == MAXALIGN(extra));
    mem = palloc(mtup->t_len + extra);
    memset(mem, 0, extra);
    result = (MinimalTuple) (mem + extra);
    memcpy(result, mtup, mtup->t_len);
    return result;
}
 
/*
 * heap_tuple_from_minimal_tuple
 *      create a HeapTuple by copying from a MinimalTuple;
 *      system columns are filled with zeroes
 *
 * The result is allocated in the current memory context.
 * The HeapTuple struct, tuple header, and tuple data are all allocated
 * as a single palloc() block.
 */
HeapTuple
heap_tuple_from_minimal_tuple(MinimalTuple mtup)
{
    HeapTuple   result;
    uint32      len = mtup->t_len + MINIMAL_TUPLE_OFFSET;
 
    result = (HeapTuple) palloc(HEAPTUPLESIZE + len);
    result->t_len = len;
    ItemPointerSetInvalid(&(result->t_self));
    result->t_tableOid = InvalidOid;
    result->t_data = (HeapTupleHeader) ((char *) result + HEAPTUPLESIZE);
    memcpy((char *) result->t_data + MINIMAL_TUPLE_OFFSET, mtup, mtup->t_len);
    memset(result->t_data, 0, offsetof(HeapTupleHeaderData, t_infomask2));
    return result;
}
 
/*
 * minimal_tuple_from_heap_tuple
 *      create a MinimalTuple by copying from a HeapTuple
 *
 * The result is allocated in the current memory context.
 */
MinimalTuple
minimal_tuple_from_heap_tuple(HeapTuple htup, Size extra)
{
    MinimalTuple result;
    char       *mem;
    uint32      len;
 
    Assert(extra == MAXALIGN(extra));
    Assert(htup->t_len > MINIMAL_TUPLE_OFFSET);
    len = htup->t_len - MINIMAL_TUPLE_OFFSET;
    mem = palloc(len + extra);
    memset(mem, 0, extra);
    result = (MinimalTuple) (mem + extra);
    memcpy(result, (char *) htup->t_data + MINIMAL_TUPLE_OFFSET, len);
 
    result->t_len = len;
    return result;
}
 
/*
 * This mainly exists so JIT can inline the definition, but it's also
 * sometimes useful in debugging sessions.
 */
size_t
varsize_any(void *p)
{
    return VARSIZE_ANY(p);
}