/*-

 * Copyright (c) 1990, 1993, 1994

 *	The Regents of the University of California.  All rights reserved.

 *

 * This code is derived from software contributed to Berkeley by

 * Mike Olson.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. All advertising materials mentioning features or use of this software

 *    must display the following acknowledgement:

 *	This product includes software developed by the University of

 *	California, Berkeley and its contributors.

 * 4. Neither the name of the University nor the names of its contributors

 *    may be used to endorse or promote products derived from this software

 *    without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 */

#if defined(LIBC_SCCS) && !defined(lint)

static char sccsid[] = "@(#)bt_split.c	8.10 (Berkeley) 1/9/95";

#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <limits.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include "db-int.h"

#include "btree.h"

static int	 bt_broot __P((BTREE *, PAGE *, PAGE *, PAGE *));

static PAGE	*bt_page

		    __P((BTREE *, PAGE *, PAGE **, PAGE **, indx_t *, size_t));

static int	 bt_preserve __P((BTREE *, db_pgno_t));

static PAGE	*bt_psplit

		    __P((BTREE *, PAGE *, PAGE *, PAGE *, indx_t *, size_t));

static PAGE	*bt_root

		    __P((BTREE *, PAGE *, PAGE **, PAGE **, indx_t *, size_t));

static int	 bt_rroot __P((BTREE *, PAGE *, PAGE *, PAGE *));

static recno_t	 rec_total __P((PAGE *));

#ifdef STATISTICS

u_long	bt_rootsplit, bt_split, bt_sortsplit, bt_pfxsaved;

#endif

/*

 * __BT_SPLIT -- Split the tree.

 *

 * Parameters:

 *	t:	tree

 *	sp:	page to split

 *	key:	key to insert

 *	data:	data to insert

 *	flags:	BIGKEY/BIGDATA flags

 *	ilen:	insert length

 *	skip:	index to leave open

 *

 * Returns:

 *	RET_ERROR, RET_SUCCESS

 */

int

__bt_split(t, sp, key, data, flags, ilen, argskip)

	BTREE *t;

	PAGE *sp;

	const DBT *key, *data;

	int flags;

	size_t ilen;

	u_int32_t argskip;

{

	BINTERNAL *bi = NULL;

	BLEAF *bl = NULL, *tbl;

	DBT a, b;

	EPGNO *parent;

	PAGE *h, *l, *r, *lchild, *rchild;

	indx_t nxtindex;

	u_int16_t skip;

	u_int32_t n, nbytes, nksize = 0;

	int parentsplit;

	char *dest;

	/*

	 * Split the page into two pages, l and r.  The split routines return

	 * a pointer to the page into which the key should be inserted and with

	 * skip set to the offset which should be used.  Additionally, l and r

	 * are pinned.

	 */

	skip = argskip;

	h = sp->pgno == P_ROOT ?

	    bt_root(t, sp, &l, &r, &skip, ilen) :

	    bt_page(t, sp, &l, &r, &skip, ilen);

	if (h == NULL)

		return (RET_ERROR);

	/*

	 * Insert the new key/data pair into the leaf page.  (Key inserts

	 * always cause a leaf page to split first.)

	 */

	h->linp[skip] = h->upper -= ilen;

	dest = (char *)h + h->upper;

	if (F_ISSET(t, R_RECNO))

		WR_RLEAF(dest, data, flags)

	else

		WR_BLEAF(dest, key, data, flags)

	/* If the root page was split, make it look right. */

	if (sp->pgno == P_ROOT &&

	    (F_ISSET(t, R_RECNO) ?

	    bt_rroot(t, sp, l, r) : bt_broot(t, sp, l, r)) == RET_ERROR)

		goto err2;

	/*

	 * Now we walk the parent page stack -- a LIFO stack of the pages that

	 * were traversed when we searched for the page that split.  Each stack

	 * entry is a page number and a page index offset.  The offset is for

	 * the page traversed on the search.  We've just split a page, so we

	 * have to insert a new key into the parent page.

	 *

	 * If the insert into the parent page causes it to split, may have to

	 * continue splitting all the way up the tree.  We stop if the root

	 * splits or the page inserted into didn't have to split to hold the

	 * new key.  Some algorithms replace the key for the old page as well

	 * as the new page.  We don't, as there's no reason to believe that the

	 * first key on the old page is any better than the key we have, and,

	 * in the case of a key being placed at index 0 causing the split, the

	 * key is unavailable.

	 *

	 * There are a maximum of 5 pages pinned at any time.  We keep the left

	 * and right pages pinned while working on the parent.   The 5 are the

	 * two children, left parent and right parent (when the parent splits)

	 * and the root page or the overflow key page when calling bt_preserve.

	 * This code must make sure that all pins are released other than the

	 * root page or overflow page which is unlocked elsewhere.

	 */

	while ((parent = BT_POP(t)) != NULL) {

		lchild = l;

		rchild = r;

		/* Get the parent page. */

		if ((h = mpool_get(t->bt_mp, parent->pgno, 0)) == NULL)

			goto err2;

	 	/*

		 * The new key goes ONE AFTER the index, because the split

		 * was to the right.

		 */

		skip = parent->index + 1;

		/*

		 * Calculate the space needed on the parent page.

		 *

		 * Prefix trees: space hack when inserting into BINTERNAL

		 * pages.  Retain only what's needed to distinguish between

		 * the new entry and the LAST entry on the page to its left.

		 * If the keys compare equal, retain the entire key.  Note,

		 * we don't touch overflow keys, and the entire key must be

		 * retained for the next-to-left most key on the leftmost

		 * page of each level, or the search will fail.  Applicable

		 * ONLY to internal pages that have leaf pages as children.

		 * Further reduction of the key between pairs of internal

		 * pages loses too much information.

		 */

		switch (rchild->flags & P_TYPE) {

		case P_BINTERNAL:

			bi = GETBINTERNAL(rchild, 0);

			nbytes = NBINTERNAL(bi->ksize);

			break;

		case P_BLEAF:

			bl = GETBLEAF(rchild, 0);

			nbytes = NBINTERNAL(bl->ksize);

			if (t->bt_pfx && !(bl->flags & P_BIGKEY) &&

			    (h->prevpg != P_INVALID || skip > 1)) {

				tbl = GETBLEAF(lchild, NEXTINDEX(lchild) - 1);

				a.size = tbl->ksize;

				a.data = tbl->bytes;

				b.size = bl->ksize;

				b.data = bl->bytes;

				nksize = t->bt_pfx(&a, &b);

				n = NBINTERNAL(nksize);

				if (n < nbytes) {

#ifdef STATISTICS

					bt_pfxsaved += nbytes - n;

#endif

					nbytes = n;

				} else

					nksize = 0;

			} else

				nksize = 0;

			break;

		case P_RINTERNAL:

		case P_RLEAF:

			nbytes = NRINTERNAL;

			break;

		default:

			abort();

		}

		/* Split the parent page if necessary or shift the indices. */

		if ((u_int32_t)h->upper - (u_int32_t)h->lower

		    < nbytes + sizeof(indx_t)) {

			sp = h;

			h = h->pgno == P_ROOT ?

			    bt_root(t, h, &l, &r, &skip, nbytes) :

			    bt_page(t, h, &l, &r, &skip, nbytes);

			if (h == NULL)

				goto err1;

			parentsplit = 1;

		} else {

			if (skip < (nxtindex = NEXTINDEX(h)))

				memmove(h->linp + skip + 1, h->linp + skip,

				    (nxtindex - skip) * sizeof(indx_t));

			h->lower += sizeof(indx_t);

			parentsplit = 0;

		}

		/* Insert the key into the parent page. */

		switch (rchild->flags & P_TYPE) {

		case P_BINTERNAL:

			h->linp[skip] = h->upper -= nbytes;

			dest = (char *)h + h->linp[skip];

			memmove(dest, bi, nbytes);

			((BINTERNAL *)(void *)dest)->pgno = rchild->pgno;

			break;

		case P_BLEAF:

			h->linp[skip] = h->upper -= nbytes;

			dest = (char *)h + h->linp[skip];

			WR_BINTERNAL(dest, nksize ? nksize : bl->ksize,

			    rchild->pgno, bl->flags & P_BIGKEY);

			memmove(dest, bl->bytes, nksize ? nksize : bl->ksize);

			if (bl->flags & P_BIGKEY) {

				db_pgno_t pgno;

				memcpy(&pgno, bl->bytes, sizeof(pgno));

				if (bt_preserve(t, pgno) == RET_ERROR)

					goto err1;

			}

			break;

		case P_RINTERNAL:

			/*

			 * Update the left page count.  If split

			 * added at index 0, fix the correct page.

			 */

			if (skip > 0)

				dest = (char *)h + h->linp[skip - 1];

			else

				dest = (char *)l + l->linp[NEXTINDEX(l) - 1];

			((RINTERNAL *)(void *)dest)->nrecs = rec_total(lchild);

			((RINTERNAL *)(void *)dest)->pgno = lchild->pgno;

			/* Update the right page count. */

			h->linp[skip] = h->upper -= nbytes;

			dest = (char *)h + h->linp[skip];

			((RINTERNAL *)(void *)dest)->nrecs = rec_total(rchild);

			((RINTERNAL *)(void *)dest)->pgno = rchild->pgno;

			break;

		case P_RLEAF:

			/*

			 * Update the left page count.  If split

			 * added at index 0, fix the correct page.

			 */

			if (skip > 0)

				dest = (char *)h + h->linp[skip - 1];

			else

				dest = (char *)l + l->linp[NEXTINDEX(l) - 1];

			((RINTERNAL *)(void *)dest)->nrecs = NEXTINDEX(lchild);

			((RINTERNAL *)(void *)dest)->pgno = lchild->pgno;

			/* Update the right page count. */

			h->linp[skip] = h->upper -= nbytes;

			dest = (char *)h + h->linp[skip];

			((RINTERNAL *)(void *)dest)->nrecs = NEXTINDEX(rchild);

			((RINTERNAL *)(void *)dest)->pgno = rchild->pgno;

			break;

		default:

			abort();

		}

		/* Unpin the held pages. */

		if (!parentsplit) {

			mpool_put(t->bt_mp, h, MPOOL_DIRTY);

			break;

		}

		/* If the root page was split, make it look right. */

		if (sp->pgno == P_ROOT &&

		    (F_ISSET(t, R_RECNO) ?

		    bt_rroot(t, sp, l, r) : bt_broot(t, sp, l, r)) == RET_ERROR)

			goto err1;

		mpool_put(t->bt_mp, lchild, MPOOL_DIRTY);

		mpool_put(t->bt_mp, rchild, MPOOL_DIRTY);

	}

	/* Unpin the held pages. */

	mpool_put(t->bt_mp, l, MPOOL_DIRTY);

	mpool_put(t->bt_mp, r, MPOOL_DIRTY);

	/* Clear any pages left on the stack. */

	return (RET_SUCCESS);

	/*

	 * If something fails in the above loop we were already walking back

	 * up the tree and the tree is now inconsistent.  Nothing much we can

	 * do about it but release any memory we're holding.

	 */

err1:	mpool_put(t->bt_mp, lchild, MPOOL_DIRTY);

	mpool_put(t->bt_mp, rchild, MPOOL_DIRTY);

err2:	mpool_put(t->bt_mp, l, 0);

	mpool_put(t->bt_mp, r, 0);

	__dbpanic(t->bt_dbp);

	return (RET_ERROR);

}

/*

 * BT_PAGE -- Split a non-root page of a btree.

 *

 * Parameters:

 *	t:	tree

 *	h:	root page

 *	lp:	pointer to left page pointer

 *	rp:	pointer to right page pointer

 *	skip:	pointer to index to leave open

 *	ilen:	insert length

 *

 * Returns:

 *	Pointer to page in which to insert or NULL on error.

 */

static PAGE *

bt_page(t, h, lp, rp, skip, ilen)

	BTREE *t;

	PAGE *h, **lp, **rp;

	indx_t *skip;

	size_t ilen;

{

	PAGE *l, *r, *tp;

	db_pgno_t npg;

#ifdef STATISTICS

	++bt_split;

#endif

	/* Put the new right page for the split into place. */

	if ((r = __bt_new(t, &npg)) == NULL)

		return (NULL);

	r->pgno = npg;

	r->lower = BTDATAOFF;

	r->upper = t->bt_psize;

	r->nextpg = h->nextpg;

	r->prevpg = h->pgno;

	r->flags = h->flags & P_TYPE;

	/*

	 * If we're splitting the last page on a level because we're appending

	 * a key to it (skip is NEXTINDEX()), it's likely that the data is

	 * sorted.  Adding an empty page on the side of the level is less work

	 * and can push the fill factor much higher than normal.  If we're

	 * wrong it's no big deal, we'll just do the split the right way next

	 * time.  It may look like it's equally easy to do a similar hack for

	 * reverse sorted data, that is, split the tree left, but it's not.

	 * Don't even try.

	 */

	if (h->nextpg == P_INVALID && *skip == NEXTINDEX(h)) {

#ifdef STATISTICS

		++bt_sortsplit;

#endif

		h->nextpg = r->pgno;

		r->lower = BTDATAOFF + sizeof(indx_t);

		*skip = 0;

		*lp = h;

		*rp = r;

		return (r);

	}

	/* Put the new left page for the split into place. */

	if ((l = (PAGE *)malloc(t->bt_psize)) == NULL) {

		mpool_put(t->bt_mp, r, 0);

		return (NULL);

	}

#if 1 /* def PURIFY */

	memset(l, 0xff, t->bt_psize);

#endif

	l->pgno = h->pgno;

	l->nextpg = r->pgno;

	l->prevpg = h->prevpg;

	l->lower = BTDATAOFF;

	l->upper = t->bt_psize;

	l->flags = h->flags & P_TYPE;

	/* Fix up the previous pointer of the page after the split page. */

	if (h->nextpg != P_INVALID) {

		if ((tp = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) {

			free(l);

			/* XXX mpool_free(t->bt_mp, r->pgno); */

			return (NULL);

		}

		tp->prevpg = r->pgno;

		mpool_put(t->bt_mp, tp, MPOOL_DIRTY);

	}

	/*

	 * Split right.  The key/data pairs aren't sorted in the btree page so

	 * it's simpler to copy the data from the split page onto two new pages

	 * instead of copying half the data to the right page and compacting

	 * the left page in place.  Since the left page can't change, we have

	 * to swap the original and the allocated left page after the split.

	 */

	tp = bt_psplit(t, h, l, r, skip, ilen);

	/* Move the new left page onto the old left page. */

	memmove(h, l, t->bt_psize);

	if (tp == l)

		tp = h;

	free(l);

	*lp = h;

	*rp = r;

	return (tp);

}

/*

 * BT_ROOT -- Split the root page of a btree.

 *

 * Parameters:

 *	t:	tree

 *	h:	root page

 *	lp:	pointer to left page pointer

 *	rp:	pointer to right page pointer

 *	skip:	pointer to index to leave open

 *	ilen:	insert length

 *

 * Returns:

 *	Pointer to page in which to insert or NULL on error.

 */

static PAGE *

bt_root(t, h, lp, rp, skip, ilen)

	BTREE *t;

	PAGE *h, **lp, **rp;

	indx_t *skip;

	size_t ilen;

{

	PAGE *l, *r, *tp;

	db_pgno_t lnpg, rnpg;

#ifdef STATISTICS

	++bt_split;

	++bt_rootsplit;

#endif

	/* Put the new left and right pages for the split into place. */

	if ((l = __bt_new(t, &lnpg)) == NULL ||

	    (r = __bt_new(t, &rnpg)) == NULL)

		return (NULL);

	l->pgno = lnpg;

	r->pgno = rnpg;

	l->nextpg = r->pgno;

	r->prevpg = l->pgno;

	l->prevpg = r->nextpg = P_INVALID;

	l->lower = r->lower = BTDATAOFF;

	l->upper = r->upper = t->bt_psize;

	l->flags = r->flags = h->flags & P_TYPE;

	/* Split the root page. */

	tp = bt_psplit(t, h, l, r, skip, ilen);

	*lp = l;

	*rp = r;

	return (tp);

}

/*

 * BT_RROOT -- Fix up the recno root page after it has been split.

 *

 * Parameters:

 *	t:	tree

 *	h:	root page

 *	l:	left page

 *	r:	right page

 *

 * Returns:

 *	RET_ERROR, RET_SUCCESS

 */

static int

bt_rroot(t, h, l, r)

	BTREE *t;

	PAGE *h, *l, *r;

{

	char *dest;

	/* Insert the left and right keys, set the header information. */

	h->linp[0] = h->upper = t->bt_psize - NRINTERNAL;

	dest = (char *)h + h->upper;

	WR_RINTERNAL(dest,

	    l->flags & P_RLEAF ? NEXTINDEX(l) : rec_total(l), l->pgno);

	h->linp[1] = h->upper -= NRINTERNAL;

	dest = (char *)h + h->upper;

	WR_RINTERNAL(dest,

	    r->flags & P_RLEAF ? NEXTINDEX(r) : rec_total(r), r->pgno);

	h->lower = BTDATAOFF + 2 * sizeof(indx_t);

	/* Unpin the root page, set to recno internal page. */

	h->flags &= ~P_TYPE;

	h->flags |= P_RINTERNAL;

	mpool_put(t->bt_mp, h, MPOOL_DIRTY);

	return (RET_SUCCESS);

}

/*

 * BT_BROOT -- Fix up the btree root page after it has been split.

 *

 * Parameters:

 *	t:	tree

 *	h:	root page

 *	l:	left page

 *	r:	right page

 *

 * Returns:

 *	RET_ERROR, RET_SUCCESS

 */

static int

bt_broot(t, h, l, r)

	BTREE *t;

	PAGE *h, *l, *r;

{

	BINTERNAL *bi;

	BLEAF *bl;

	u_int32_t nbytes;

	char *dest;

	/*

	 * If the root page was a leaf page, change it into an internal page.

	 * We copy the key we split on (but not the key's data, in the case of

	 * a leaf page) to the new root page.

	 *

	 * The btree comparison code guarantees that the left-most key on any

	 * level of the tree is never used, so it doesn't need to be filled in.

	 */

	nbytes = NBINTERNAL(0);

	h->linp[0] = h->upper = t->bt_psize - nbytes;

	dest = (char *)h + h->upper;

	WR_BINTERNAL(dest, 0, l->pgno, 0);

	switch (h->flags & P_TYPE) {

	case P_BLEAF:

		bl = GETBLEAF(r, 0);

		nbytes = NBINTERNAL(bl->ksize);

		h->linp[1] = h->upper -= nbytes;

		dest = (char *)h + h->upper;

		WR_BINTERNAL(dest, bl->ksize, r->pgno, 0);

		memmove(dest, bl->bytes, bl->ksize);

		/*

		 * If the key is on an overflow page, mark the overflow chain

		 * so it isn't deleted when the leaf copy of the key is deleted.

		 */

		if (bl->flags & P_BIGKEY) {

			db_pgno_t pgno;

			memcpy(&pgno, bl->bytes, sizeof(pgno));

			if (bt_preserve(t, pgno) == RET_ERROR)

				return (RET_ERROR);

		}

		break;

	case P_BINTERNAL:

		bi = GETBINTERNAL(r, 0);

		nbytes = NBINTERNAL(bi->ksize);

		h->linp[1] = h->upper -= nbytes;

		dest = (char *)h + h->upper;

		memmove(dest, bi, nbytes);

		((BINTERNAL *)(void *)dest)->pgno = r->pgno;

		break;

	default:

		abort();

	}

	/* There are two keys on the page. */

	h->lower = BTDATAOFF + 2 * sizeof(indx_t);

	/* Unpin the root page, set to btree internal page. */

	h->flags &= ~P_TYPE;

	h->flags |= P_BINTERNAL;

	mpool_put(t->bt_mp, h, MPOOL_DIRTY);

	return (RET_SUCCESS);

}

/*

 * BT_PSPLIT -- Do the real work of splitting the page.

 *

 * Parameters:

 *	t:	tree

 *	h:	page to be split

 *	l:	page to put lower half of data

 *	r:	page to put upper half of data

 *	pskip:	pointer to index to leave open

 *	ilen:	insert length

 *

 * Returns:

 *	Pointer to page in which to insert.

 */

static PAGE *

bt_psplit(t, h, l, r, pskip, ilen)

	BTREE *t;

	PAGE *h, *l, *r;

	indx_t *pskip;

	size_t ilen;

{

	BINTERNAL *bi;

	BLEAF *bl;

	CURSOR *c;

	RLEAF *rl;

	PAGE *rval;

	void *src;

	indx_t full, half, nxt, off, skip, top, used;

	u_int32_t nbytes;

	int bigkeycnt, isbigkey;

	/*

	 * Split the data to the left and right pages.  Leave the skip index

	 * open.  Additionally, make some effort not to split on an overflow

	 * key.  This makes internal page processing faster and can save

	 * space as overflow keys used by internal pages are never deleted.

	 */

	bigkeycnt = 0;

	skip = *pskip;

	full = t->bt_psize - BTDATAOFF;

	half = full / 2;

	used = 0;

	src = NULL;	     /* silence gcc "uninitialized" warning */

	for (nxt = off = 0, top = NEXTINDEX(h); nxt < top; ++off) {

		if (skip == off) {

			nbytes = ilen;

			isbigkey = 0;		/* XXX: not really known. */

		} else

			switch (h->flags & P_TYPE) {

			case P_BINTERNAL:

				src = bi = GETBINTERNAL(h, nxt);

				nbytes = NBINTERNAL(bi->ksize);

				isbigkey = bi->flags & P_BIGKEY;

				break;

			case P_BLEAF:

				src = bl = GETBLEAF(h, nxt);

				nbytes = NBLEAF(bl);

				isbigkey = bl->flags & P_BIGKEY;

				break;

			case P_RINTERNAL:

				src = GETRINTERNAL(h, nxt);

				nbytes = NRINTERNAL;

				isbigkey = 0;

				break;

			case P_RLEAF:

				src = rl = GETRLEAF(h, nxt);

				nbytes = NRLEAF(rl);

				isbigkey = 0;

				break;

			default:

				abort();

			}

		/*

		 * If the key/data pairs are substantial fractions of the max

		 * possible size for the page, it's possible to get situations

		 * where we decide to try and copy too much onto the left page.

		 * Make sure that doesn't happen.

		 */

		if ((skip <= off && used + nbytes + sizeof(indx_t) >= full)

		    || nxt == top - 1) {

			--off;

			break;

		}

		/* Copy the key/data pair, if not the skipped index. */

		if (skip != off) {

			++nxt;

			l->linp[off] = l->upper -= nbytes;

			memmove((char *)l + l->upper, src, nbytes);

		}

		used += nbytes + sizeof(indx_t);

		if (used >= half) {

			if (!isbigkey || bigkeycnt == 3)

				break;

			else

				++bigkeycnt;

		}

	}

	/*

	 * Off is the last offset that's valid for the left page.

	 * Nxt is the first offset to be placed on the right page.

	 */

	l->lower += (off + 1) * sizeof(indx_t);

	/*

	 * If splitting the page that the cursor was on, the cursor has to be

	 * adjusted to point to the same record as before the split.  If the

	 * cursor is at or past the skipped slot, the cursor is incremented by

	 * one.  If the cursor is on the right page, it is decremented by the

	 * number of records split to the left page.

	 */

	c = &t->bt_cursor;

	if (F_ISSET(c, CURS_INIT) && c->pg.pgno == h->pgno) {

		if (c->pg.index >= skip)

			++c->pg.index;

		if (c->pg.index < nxt)			/* Left page. */

			c->pg.pgno = l->pgno;

		else {					/* Right page. */

			c->pg.pgno = r->pgno;

			c->pg.index -= nxt;

		}

	}

	/*

	 * If the skipped index was on the left page, just return that page.

	 * Otherwise, adjust the skip index to reflect the new position on

	 * the right page.

	 */

	if (skip <= off) {

		skip = (indx_t)-1;

		rval = l;

	} else {

		rval = r;

		*pskip -= nxt;

	}

	for (off = 0; nxt < top; ++off) {

		if (skip == nxt) {

			++off;

			skip = (indx_t)-1;

		}

		switch (h->flags & P_TYPE) {

		case P_BINTERNAL:

			src = bi = GETBINTERNAL(h, nxt);

			nbytes = NBINTERNAL(bi->ksize);

			break;

		case P_BLEAF:

			src = bl = GETBLEAF(h, nxt);

			nbytes = NBLEAF(bl);

			break;

		case P_RINTERNAL:

			src = GETRINTERNAL(h, nxt);

			nbytes = NRINTERNAL;

			break;

		case P_RLEAF:

			src = rl = GETRLEAF(h, nxt);

			nbytes = NRLEAF(rl);

			break;

		default:

			abort();

		}

		++nxt;

		r->linp[off] = r->upper -= nbytes;

		memmove((char *)r + r->upper, src, nbytes);

	}

	r->lower += off * sizeof(indx_t);

	/* If the key is being appended to the page, adjust the index. */

	if (skip == top)

		r->lower += sizeof(indx_t);

	return (rval);

}

/*

 * BT_PRESERVE -- Mark a chain of pages as used by an internal node.

 *

 * Chains of indirect blocks pointed to by leaf nodes get reclaimed when the

 * record that references them gets deleted.  Chains pointed to by internal

 * pages never get deleted.  This routine marks a chain as pointed to by an

 * internal page.

 *

 * Parameters:

 *	t:	tree

 *	pg:	page number of first page in the chain.

 *

 * Returns:

 *	RET_SUCCESS, RET_ERROR.

 */

static int

bt_preserve(t, pg)

	BTREE *t;

	db_pgno_t pg;

{

	PAGE *h;

	if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)

		return (RET_ERROR);

	h->flags |= P_PRESERVE;

	mpool_put(t->bt_mp, h, MPOOL_DIRTY);

	return (RET_SUCCESS);

}

/*

 * REC_TOTAL -- Return the number of recno entries below a page.

 *

 * Parameters:

 *	h:	page

 *

 * Returns:

 *	The number of recno entries below a page.

 *

 * XXX

 * These values could be set by the bt_psplit routine.  The problem is that the

 * entry has to be popped off of the stack etc. or the values have to be passed

 * all the way back to bt_split/bt_rroot and it's not very clean.

 */

static recno_t

rec_total(h)

	PAGE *h;

{

	recno_t recs;

	indx_t nxt, top;

	for (recs = 0, nxt = 0, top = NEXTINDEX(h); nxt < top; ++nxt)

		recs += GETRINTERNAL(h, nxt)->nrecs;

	return (recs);

}