heaptuple.c

/*-------------------------------------------------------------------------
 *
 * heaptuple.c--
 *    This file contains heap tuple accessor and mutator routines, as well
 *    as a few various tuple utilities.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/access/common/heaptuple.c,v 1.13 1996/11/03 08:16:44 scrappy Exp $
 *
 * NOTES
 *    The old interface functions have been converted to macros
 *    and moved to heapam.h
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup.h"
#include "access/transam.h"
#include "access/tupmacs.h"
#include "storage/bufpage.h"
#include "utils/memutils.h"
#include "utils/palloc.h"

#ifndef HAVE_MEMMOVE
# include "regex/utils.h"
#else
# include <string.h>
#endif


/* this is so the sparcstation debugger works */

#if !defined(NO_ASSERT_CHECKING) && defined(sparc)
#define register
#endif /* !NO_ASSERT_CHECKING && sparc */

/* ----------------------------------------------------------------
 *			misc support routines
 * ----------------------------------------------------------------
 */

/* ----------------
 *	ComputeDataSize
 * ----------------
 */
Size
ComputeDataSize(TupleDesc tupleDesc,
		Datum value[],
		char nulls[])
{
    uint32 data_length;
    int i;
    int numberOfAttributes = tupleDesc->natts;
    AttributeTupleForm *att = tupleDesc->attrs;
    
    for (data_length = 0, i = 0; i < numberOfAttributes; i++) {
	if (nulls[i] != ' ') continue;
	    
	switch (att[i]->attlen) {
	case -1:
	    /*
	     * This is the size of the disk representation and so
	     * must include the additional sizeof long.
	     */
	    if (att[i]->attalign == 'd') {
		data_length = DOUBLEALIGN(data_length)
		    + VARSIZE(DatumGetPointer(value[i]));
	    } else {
		data_length = INTALIGN(data_length)
		    + VARSIZE(DatumGetPointer(value[i]));
	    }
	    break;
	case sizeof(char):
	    data_length++;
	    break;
	case sizeof(short):
	    data_length = SHORTALIGN(data_length + sizeof(short));
	    break;
	case sizeof(int32):
	    data_length = INTALIGN(data_length + sizeof(int32));
	    break;
	default:
	    if (att[i]->attlen < sizeof(int32))
		elog(WARN, "ComputeDataSize: attribute %d has len %d",
		     i, att[i]->attlen);
	    if (att[i]->attalign == 'd')
		data_length = DOUBLEALIGN(data_length) + att[i]->attlen;
	    else
		data_length = LONGALIGN(data_length) + att[i]->attlen;
	    break;
	}
    }
    
    return data_length;
}

/* ----------------
 *	DataFill
 * ----------------
 */
void
DataFill(char *data,
	 TupleDesc tupleDesc,
	 Datum value[],
	 char nulls[],
	 char *infomask,
	 bits8 *bit)
{
    bits8				*bitP = 0;
    int					bitmask = 0;
    uint32				data_length;
    int		i;
    int         numberOfAttributes = tupleDesc->natts;
    AttributeTupleForm	*att = tupleDesc->attrs;
    
    if (bit != NULL) {
	bitP = &bit[-1];
	bitmask = CSIGNBIT;
    }
    
    *infomask = 0;
    
    for (i = 0; i < numberOfAttributes; i++) {
	if (bit != NULL) {
	    if (bitmask != CSIGNBIT) {
		bitmask <<= 1;
	    } else {
		bitP += 1;
		*bitP = 0x0;
		bitmask = 1;
	    }
	    
	    if (nulls[i] == 'n') {
		*infomask |= HEAP_HASNULL;
		continue;
	    }
	    
	    *bitP |= bitmask;
	}
	    
	switch (att[i]->attlen) {
	case -1:
	    *infomask |= HEAP_HASVARLENA;
	    if (att[i]->attalign=='d') {
		data = (char *) DOUBLEALIGN(data);
	    } else {
		data = (char *) INTALIGN(data);
	    }
	    		data_length = VARSIZE(DatumGetPointer(value[i]));
	    		memmove(data, DatumGetPointer(value[i]),data_length);
	    		data += data_length;
	    break;
	case sizeof(char):
	    *data = att[i]->attbyval ?
		DatumGetChar(value[i]) : *((char *) value[i]);
	    data += sizeof(char);
	    break;
	case sizeof(int16):
	    data = (char *) SHORTALIGN(data);
	    * (short *) data = (att[i]->attbyval ?
				DatumGetInt16(value[i]) :
				*((short *) value[i]));
	    data += sizeof(short);
	    break;
	case sizeof(int32):
	    data = (char *) INTALIGN(data);
	    * (int32 *) data = (att[i]->attbyval ?
				DatumGetInt32(value[i]) :
				*((int32 *) value[i]));
	    data += sizeof(int32);
	    break;
	default:
	    if (att[i]->attlen < sizeof(int32))
		elog(WARN, "DataFill: attribute %d has len %d",
		     i, att[i]->attlen);
	    if (att[i]->attalign == 'd') {
		data = (char *) DOUBLEALIGN(data);
		memmove(data, DatumGetPointer(value[i]),
			att[i]->attlen);
		data += att[i]->attlen;
	    } else {
		data = (char *) LONGALIGN(data);
		memmove(data, DatumGetPointer(value[i]),
			att[i]->attlen);
		data += att[i]->attlen;
	    }
				break;
	}
    }
}

/* ----------------------------------------------------------------
 *			heap tuple interface
 * ----------------------------------------------------------------
 */

/* ----------------
 *	heap_attisnull	- returns 1 iff tuple attribute is not present
 * ----------------
 */
int
heap_attisnull(HeapTuple tup, int attnum)
{
    if (attnum > (int)tup->t_natts)
	return (1);
    
    if (HeapTupleNoNulls(tup)) return(0);
    
    if (attnum > 0) {
	return(att_isnull(attnum - 1, tup->t_bits));
    } else
	switch (attnum) {
	case SelfItemPointerAttributeNumber:
	case ObjectIdAttributeNumber:
	case MinTransactionIdAttributeNumber:
	case MinCommandIdAttributeNumber:
	case MaxTransactionIdAttributeNumber:
	case MaxCommandIdAttributeNumber:
	case ChainItemPointerAttributeNumber:
	case AnchorItemPointerAttributeNumber:
	case MinAbsoluteTimeAttributeNumber:
	case MaxAbsoluteTimeAttributeNumber:
	case VersionTypeAttributeNumber:
	    break;
	    
	case 0:
	    elog(WARN, "heap_attisnull: zero attnum disallowed");
	    
	default:
	    elog(WARN, "heap_attisnull: undefined negative attnum");
	}
    
    return (0);
}

/* ----------------------------------------------------------------
 *		 system attribute heap tuple support
 * ----------------------------------------------------------------
 */

/* ----------------
 *	heap_sysattrlen
 *
 *	This routine returns the length of a system attribute.
 * ----------------
 */
int
heap_sysattrlen(AttrNumber attno)
{
    HeapTupleData	*f = NULL;

    switch (attno) {
		case SelfItemPointerAttributeNumber:	return sizeof f->t_ctid;
		case ObjectIdAttributeNumber:			return sizeof f->t_oid;
		case MinTransactionIdAttributeNumber:	return sizeof f->t_xmin;
		case MinCommandIdAttributeNumber:		return sizeof f->t_cmin;
		case MaxTransactionIdAttributeNumber:	return sizeof f->t_xmax;
		case MaxCommandIdAttributeNumber:		return sizeof f->t_cmax;
		case ChainItemPointerAttributeNumber:	return sizeof f->t_chain;
		case MinAbsoluteTimeAttributeNumber:	return sizeof f->t_tmin;
		case MaxAbsoluteTimeAttributeNumber:	return sizeof f->t_tmax;
		case VersionTypeAttributeNumber:		return sizeof f->t_vtype;

    case AnchorItemPointerAttributeNumber:
	elog(WARN, "heap_sysattrlen: field t_anchor does not exist!");
			return 0;

    default:
			elog(WARN, "sysattrlen: System attribute number %d unknown.", attno);
			return 0;
    }
}

/* ----------------
 *	heap_sysattrbyval
 *
 *	This routine returns the "by-value" property of a system attribute.
 * ----------------
 */
bool
heap_sysattrbyval(AttrNumber attno)
{
    bool		byval;
    
    switch (attno) {
    case SelfItemPointerAttributeNumber:
	byval = false;
	break;
    case ObjectIdAttributeNumber:
	byval = true;
	break;
    case MinTransactionIdAttributeNumber:
	byval = true;
	break;
    case MinCommandIdAttributeNumber:
	byval = true;
	break;
    case MaxTransactionIdAttributeNumber:
	byval = true;
	break;
    case MaxCommandIdAttributeNumber:
	byval = true;
	break;
    case ChainItemPointerAttributeNumber:
	byval = false;
	break;
    case AnchorItemPointerAttributeNumber:
	byval = false;
	break;
    case MinAbsoluteTimeAttributeNumber:
	byval = true;
	break;
    case MaxAbsoluteTimeAttributeNumber:
	byval = true;
	break;
    case VersionTypeAttributeNumber:
	byval = true;
	break;
    default:
	byval = true;
	elog(WARN, "sysattrbyval: System attribute number %d unknown.",
	     attno);
	break;
    }
    
    return byval;
}

/* ----------------
 *	heap_getsysattr
 * ----------------
 */
char *
heap_getsysattr(HeapTuple tup, Buffer b, int attnum)
{
    switch (attnum) {
    case SelfItemPointerAttributeNumber:
	return ((char *)&tup->t_ctid);
    case ObjectIdAttributeNumber:
	return ((char *) (long) tup->t_oid);
    case MinTransactionIdAttributeNumber:
	return ((char *) (long) tup->t_xmin);
    case MinCommandIdAttributeNumber:
	return ((char *) (long) tup->t_cmin);
    case MaxTransactionIdAttributeNumber:
	return ((char *) (long) tup->t_xmax);
    case MaxCommandIdAttributeNumber:
	return ((char *) (long) tup->t_cmax);
    case ChainItemPointerAttributeNumber:
	return ((char *) &tup->t_chain);
    case AnchorItemPointerAttributeNumber:
	elog(WARN, "heap_getsysattr: t_anchor does not exist!");
	break;
	
	/*
	 *  For tmin and tmax, we need to do some extra work.  These don't
	 *  get filled in until the vacuum cleaner runs (or we manage to flush
	 *  a page after setting the value correctly below).  If the vacuum
	 *  cleaner hasn't run yet, then the times stored in the tuple are
	 *  wrong, and we need to look up the commit time of the transaction.
	 *  We cache this value in the tuple to avoid doing the work more than
	 *  once.
	 */
	
    case MinAbsoluteTimeAttributeNumber:
	if (!AbsoluteTimeIsBackwardCompatiblyValid(tup->t_tmin) &&
	    TransactionIdDidCommit(tup->t_xmin))
	    tup->t_tmin = TransactionIdGetCommitTime(tup->t_xmin);
	return ((char *) (long) tup->t_tmin);
    case MaxAbsoluteTimeAttributeNumber:
	if (!AbsoluteTimeIsBackwardCompatiblyReal(tup->t_tmax)) {
	    if (TransactionIdDidCommit(tup->t_xmax))
		tup->t_tmax = TransactionIdGetCommitTime(tup->t_xmax);
	    else
		tup->t_tmax = CURRENT_ABSTIME;
	}
	return ((char *) (long) tup->t_tmax);
    case VersionTypeAttributeNumber:
	return ((char *) (long) tup->t_vtype);
    default:
	elog(WARN, "heap_getsysattr: undefined attnum %d", attnum);
    }
    return(NULL);
}

/* ----------------
 *	fastgetattr
 *
 *	This is a newer version of fastgetattr which attempts to be
 *	faster by caching attribute offsets in the attribute descriptor.
 *
 *	an alternate way to speed things up would be to cache offsets
 *	with the tuple, but that seems more difficult unless you take
 *	the storage hit of actually putting those offsets into the
 *	tuple you send to disk.  Yuck.
 *
 *	This scheme will be slightly slower than that, but should
 *	preform well for queries which hit large #'s of tuples.  After
 *	you cache the offsets once, examining all the other tuples using
 *	the same attribute descriptor will go much quicker. -cim 5/4/91
 * ----------------
 */
char *
fastgetattr(HeapTuple tup,
	    int attnum,
	    TupleDesc tupleDesc,
	    bool *isnull)
{
    char *tp;		/* ptr to att in tuple */
    bits8  *bp = NULL;	        /* ptr to att in tuple */
    int slow;		/* do we have to walk nulls? */
    AttributeTupleForm *att = tupleDesc->attrs;
    
    /* ----------------
     *	sanity checks
     * ----------------
     */
    
    Assert(PointerIsValid(isnull));
    Assert(attnum > 0);
    
    /* ----------------
     *   Three cases:
     * 
     *   1: No nulls and no variable length attributes.
     *   2: Has a null or a varlena AFTER att.
     *   3: Has nulls or varlenas BEFORE att.
     * ----------------
     */
    
    *isnull =  false;
    
    if (HeapTupleNoNulls(tup)) {
	attnum--;
	if (att[attnum]->attcacheoff > 0) {
	    return (char *)
		fetchatt( &(att[attnum]),
			 (char *)tup + tup->t_hoff + att[attnum]->attcacheoff);
	} else if (attnum == 0) {
	    /*
	     * first attribute is always at position zero
	     */
	    return((char *) fetchatt(&(att[0]), (char *) tup + tup->t_hoff));
	}
	    
	tp = (char *) tup + tup->t_hoff;
	    
	slow = 0;
    } else {
	/*
	 * there's a null somewhere in the tuple
	 */

	bp = tup->t_bits;
	tp = (char *) tup + tup->t_hoff;
	slow = 0;
	attnum--;
	    
	/* ----------------
	 *	check to see if desired att is null
	 * ----------------
	 */
	
	if (att_isnull(attnum, bp)) {
	    *isnull = true;
	    return NULL;
	}

	/* ----------------
	 *      Now check to see if any preceeding bits are null...
	 * ----------------
	 */
	
	{
	    register int  i = 0; /* current offset in bp */
		
	    for (i = 0; i < attnum && !slow; i++) {
		if (att_isnull(i, bp)) slow = 1;
	    }
	}
    }
    
    /*
     * now check for any non-fixed length attrs before our attribute
     */
    if (!slow) {
	if (att[attnum]->attcacheoff > 0) {
	    return (char *)
		fetchatt(&(att[attnum]),
			 tp + att[attnum]->attcacheoff);
	} else if (attnum == 0) {
	    return (char *)
		fetchatt(&(att[0]), (char *) tup + tup->t_hoff);
	} else if (!HeapTupleAllFixed(tup)) {
	    register int j = 0;
		    
	    for (j = 0; j < attnum && !slow; j++)
		if (att[j]->attlen < 1) slow = 1;
	}
    }
    
    /*
     * if slow is zero, and we got here, we know that we have a tuple with
     * no nulls.  We also have to initialize the remainder of
     * the attribute cached offset values.
     */
    if (!slow) {
	register int j = 1;
	register long off;
	    
	/*
	 * need to set cache for some atts
	 */
	    
	att[0]->attcacheoff = 0;
	
	while (att[j]->attcacheoff > 0) j++;
	
	off = att[j-1]->attcacheoff + att[j-1]->attlen;
	
	for (; j < attnum + 1; j++) {
	    switch(att[j]->attlen) {
	    case -1:
		off = (att[j]->attalign=='d') ?
		    DOUBLEALIGN(off) : INTALIGN(off);
		break;
	    case sizeof(char):
		break;
	    case sizeof(short):
		off = SHORTALIGN(off);
		break;
	    case sizeof(int32):
		off = INTALIGN(off);
		break;
	    default:
		if (att[j]->attlen < sizeof(int32)) {
		    elog(WARN,
			 "fastgetattr: attribute %d has len %d",
			 j, att[j]->attlen);
		}
		if (att[j]->attalign == 'd')
		    off = DOUBLEALIGN(off);
		else
		    off = LONGALIGN(off);
		break;
	    }
		    
	    att[j]->attcacheoff = off;
	    off += att[j]->attlen;
	}
	
	return
	    (char *)fetchatt(&(att[attnum]), tp + att[attnum]->attcacheoff);
    } else {
	register bool usecache = true;
	register int off = 0;
	register int i;
	
	/*
	 * Now we know that we have to walk the tuple CAREFULLY.
	 *
	 * Note - This loop is a little tricky.  On iteration i we
	 * first set the offset for attribute i and figure out how much
	 * the offset should be incremented.  Finally, we need to align the
	 * offset based on the size of attribute i+1 (for which the offset
	 * has been computed). -mer 12 Dec 1991
	 */
	
	for (i = 0; i < attnum; i++) {
	    if (!HeapTupleNoNulls(tup)) {
		if (att_isnull(i, bp)) {
		    usecache = false;
		    continue;
		}
	    }
	    switch (att[i]->attlen) {
	    case -1:
		off = (att[i]->attalign=='d') ?
		    DOUBLEALIGN(off) : INTALIGN(off);
		break;
	    case sizeof(char):
		break;
	    case sizeof(short):
		off = SHORTALIGN(off);
		break;
	    case sizeof(int32):
		off = INTALIGN(off);
		break;
	    default:
		if (att[i]->attlen < sizeof(int32))
		    elog(WARN,
			 "fastgetattr2: attribute %d has len %d",
			 i, att[i]->attlen);
		if (att[i]->attalign == 'd')
		    off = DOUBLEALIGN(off);
		else
		    off = LONGALIGN(off);
		break;
	    }
	    if (usecache && att[i]->attcacheoff > 0) {
		off = att[i]->attcacheoff;
		if (att[i]->attlen == -1) {
		    usecache = false;
		}
	    } else {
		if (usecache) att[i]->attcacheoff = off;
	    }
		    
	    switch(att[i]->attlen) {
	    case sizeof(char):
		off++;
		break;
	    case sizeof(int16):
		off += sizeof(int16);
		break;
	    case sizeof(int32):
		off += sizeof(int32);
		break;
	    case -1:
		usecache = false;
		off += VARSIZE(tp + off);
		break;
	    default:
		off += att[i]->attlen;
		break;
	    }
	}
	switch (att[attnum]->attlen) {
	case -1:
	    off = (att[attnum]->attalign=='d')?
		DOUBLEALIGN(off) : INTALIGN(off);
	    break;
	case sizeof(char):
	    break;
	case sizeof(short):
	    off = SHORTALIGN(off);
	    break;
	case sizeof(int32):
	    off = INTALIGN(off);
	    break;
	default:
	    if (att[attnum]->attlen < sizeof(int32))
		elog(WARN, "fastgetattr3: attribute %d has len %d",
		     attnum, att[attnum]->attlen);
	    if (att[attnum]->attalign == 'd')
		off = DOUBLEALIGN(off);
	    else
		off = LONGALIGN(off);
	    break;
	}
	return((char *) fetchatt(&(att[attnum]), tp + off));
    }
}

/* ----------------
 *	heap_getattr
 *
 *	returns an attribute from a heap tuple.  uses 
 * ----------------
 */
char *
heap_getattr(HeapTuple tup,
	     Buffer b,
	     int attnum,
	     TupleDesc tupleDesc,
	     bool *isnull)
{
    bool	localIsNull;

    /* ----------------
     *	sanity checks
     * ----------------
     */
    Assert(tup != NULL);
    
    if (! PointerIsValid(isnull))
	isnull = &localIsNull;
    
    if (attnum > (int) tup->t_natts) {
	*isnull = true;
	return ((char *) NULL);
    }
    
    /* ----------------
     *	take care of user defined attributes
     * ----------------
     */
    if (attnum > 0) {
	char  *datum;
	datum = fastgetattr(tup, attnum, tupleDesc, isnull);
	
	return (datum);
    }
    
    /* ----------------
     *	take care of system attributes
     * ----------------
     */
    *isnull = false;
    return
	heap_getsysattr(tup, b, attnum);
}

/* ----------------
 *	heap_copytuple
 *
 *	returns a copy of an entire tuple
 * ----------------
 */
HeapTuple
heap_copytuple(HeapTuple tuple)
{
    HeapTuple	newTuple;

    if (! HeapTupleIsValid(tuple))
	return (NULL);
    
    /* XXX For now, just prevent an undetectable executor related error */
    if (tuple->t_len > MAXTUPLEN) {
	elog(WARN, "palloctup: cannot handle length %d tuples",
	     tuple->t_len);
    }
    
    newTuple = (HeapTuple) palloc(tuple->t_len);
    memmove((char *) newTuple, (char *) tuple, (int) tuple->t_len);
    return(newTuple);
}

/* ----------------
 *	heap_deformtuple
 *
 *	the inverse of heap_formtuple (see below)
 * ----------------
 */
void
heap_deformtuple(HeapTuple tuple,
		 TupleDesc tdesc,
		 Datum values[],
		 char nulls[])
{
    int i;
    int natts;
    
    Assert(HeapTupleIsValid(tuple));
    
    natts = tuple->t_natts;
    for (i = 0; i<natts; i++) {
	bool isnull;
	    
	values[i] = (Datum)heap_getattr(tuple,
					InvalidBuffer,
					i+1,
					tdesc,
					&isnull);
	if (isnull)
	    nulls[i] = 'n';
	else
	    nulls[i] = ' ';
    }
}

/* ----------------
 *	heap_formtuple 
 *
 *	constructs a tuple from the given value[] and null[] arrays
 *
 * old comments
 *	Handles alignment by aligning 2 byte attributes on short boundries
 *	and 3 or 4 byte attributes on long word boundries on a vax; and
 *	aligning non-byte attributes on short boundries on a sun.  Does
 *	not properly align fixed length arrays of 1 or 2 byte types (yet).
 *
 *	Null attributes are indicated by a 'n' in the appropriate byte
 *	of the null[].  Non-null attributes are indicated by a ' ' (space).
 *
 *	Fix me.  (Figure that must keep context if debug--allow give oid.)
 *	Assumes in order.
 * ----------------
 */
HeapTuple
heap_formtuple(TupleDesc tupleDescriptor,
	       Datum value[],
	       char nulls[])
{
    char	*tp;	/* tuple pointer */
    HeapTuple	tuple;	/* return tuple */
    int		bitmaplen;
    long	len;
    int		hoff;
    bool	hasnull = false;
    int		i;
    int         numberOfAttributes = tupleDescriptor->natts;    

    len = sizeof *tuple - sizeof tuple->t_bits;
    
    for (i = 0; i < numberOfAttributes && !hasnull; i++) {
	if (nulls[i] != ' ') hasnull = true;
    }
    
    if (numberOfAttributes > MaxHeapAttributeNumber)
	elog(WARN, "heap_formtuple: numberOfAttributes of %d > %d",
	     numberOfAttributes, MaxHeapAttributeNumber);
    
    if (hasnull) {
	bitmaplen = BITMAPLEN(numberOfAttributes);
	len       += bitmaplen;
    }

    hoff = len = DOUBLEALIGN(len);	/* be conservative here */

    len += ComputeDataSize(tupleDescriptor, value, nulls);
    
    tp = (char *) palloc(len);
    tuple = (HeapTuple) tp;

    memset(tp, 0, (int)len);
    
    tuple->t_len = 	len;
    tuple->t_natts = 	numberOfAttributes;
    tuple->t_hoff = hoff;
    tuple->t_tmin = INVALID_ABSTIME;
    tuple->t_tmax = CURRENT_ABSTIME;
    
    DataFill((char *)tuple + tuple->t_hoff,
	     tupleDescriptor,
	     value,
	     nulls,
             &tuple->t_infomask,
	     (hasnull ? tuple->t_bits : NULL));
    
    return (tuple);
}

/* ----------------
 *	heap_modifytuple
 *
 *	forms a new tuple from an old tuple and a set of replacement values.
 * ----------------
 */
HeapTuple
heap_modifytuple(HeapTuple tuple,
		 Buffer buffer,
		 Relation relation,
		 Datum replValue[],
		 char replNull[],
		 char repl[])
{
    int		attoff;
    int		numberOfAttributes;
    Datum	*value;
    char	*nulls;
    bool	isNull;
    HeapTuple	newTuple;
    int		madecopy;
    uint8	infomask;
    
    /* ----------------
     *	sanity checks
     * ----------------
     */
    Assert(HeapTupleIsValid(tuple));
    Assert(BufferIsValid(buffer) || RelationIsValid(relation));
    Assert(HeapTupleIsValid(tuple));
    Assert(PointerIsValid(replValue));
    Assert(PointerIsValid(replNull));
    Assert(PointerIsValid(repl));
    
    /* ----------------
     *	if we're pointing to a disk page, then first
     *  make a copy of our tuple so that all the attributes
     *  are available.  XXX this is inefficient -cim
     * ----------------
     */
    madecopy = 0;
    if (BufferIsValid(buffer) == true) {
	relation = 	(Relation) BufferGetRelation(buffer);
	tuple = 	heap_copytuple(tuple);
	madecopy = 1;
    }
    
    numberOfAttributes = RelationGetRelationTupleForm(relation)->relnatts;
    
    /* ----------------
     *	allocate and fill value[] and nulls[] arrays from either
     *  the tuple or the repl information, as appropriate.
     * ----------------
     */
    value = (Datum *)	palloc(numberOfAttributes * sizeof *value);
    nulls =  (char *)	palloc(numberOfAttributes * sizeof *nulls);
    
    for (attoff = 0;
	 attoff < numberOfAttributes;
	 attoff += 1) {
	
	if (repl[attoff] == ' ') {
	    char *attr;

	    attr =
		heap_getattr(tuple,
			     InvalidBuffer, 
			     AttrOffsetGetAttrNumber(attoff),
			     RelationGetTupleDescriptor(relation),
			     &isNull) ;
	    value[attoff] = PointerGetDatum(attr);
	    nulls[attoff] = (isNull) ? 'n' : ' ';
	    
	} else if (repl[attoff] != 'r') {
	    elog(WARN, "heap_modifytuple: repl is \\%3d", repl[attoff]);
	    
	} else { /* == 'r' */
	    value[attoff] = replValue[attoff];
	    nulls[attoff] =  replNull[attoff];
	}
    }
    
    /* ----------------
     *	create a new tuple from the values[] and nulls[] arrays
     * ----------------
     */
    newTuple = heap_formtuple(RelationGetTupleDescriptor(relation),
			      value,
			      nulls);
    
    /* ----------------
     *	copy the header except for t_len, t_natts, t_hoff, t_bits, t_infomask
     * ----------------
     */
    infomask = newTuple->t_infomask;
    memmove((char *) &newTuple->t_ctid,	/*XXX*/
	    (char *) &tuple->t_ctid,
	    ((char *) &tuple->t_hoff - (char *) &tuple->t_ctid)); /*XXX*/
    newTuple->t_infomask = infomask;
    newTuple->t_natts = numberOfAttributes;	/* fix t_natts just in case */
    
    /* ----------------
     *	if we made a copy of the tuple, then free it.
     * ----------------
     */
    if (madecopy)
	pfree(tuple);
    
    return
	newTuple;
}

/* ----------------------------------------------------------------
 *			other misc functions
 * ----------------------------------------------------------------
 */

HeapTuple
heap_addheader(uint32 natts,	/* max domain index */
	       int structlen,	/* its length */
	       char *structure)	/* pointer to the struct */
{
    register char	*tp;	/* tuple data pointer */
    HeapTuple		tup;
    long		len;
    int			hoff;
    
    AssertArg(natts > 0);
    
    len = sizeof (HeapTupleData) - sizeof (tup->t_bits);
    
    hoff = len = DOUBLEALIGN(len);	/* be conservative */
    len += structlen;
    tp = (char *) palloc(len);
    tup = (HeapTuple) tp;
    memset((char*)tup, 0, len);
    
    tup->t_len = (short) len;			/* XXX */
    tp += tup->t_hoff = hoff;
    tup->t_natts = natts;
    tup->t_infomask = 0;
    
    memmove(tp, structure, structlen);
    
    return (tup);
}