1 #pragma ident	"%Z%%M%	%I%	%E% SMI"
2 
3 /*-
4  * Copyright (c) 1990, 1993, 1994
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * This code is derived from software contributed to Berkeley by
8  * Mike Olson.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  * 3. All advertising materials mentioning features or use of this software
19  *    must display the following acknowledgement:
20  *	This product includes software developed by the University of
21  *	California, Berkeley and its contributors.
22  * 4. Neither the name of the University nor the names of its contributors
23  *    may be used to endorse or promote products derived from this software
24  *    without specific prior written permission.
25  *
26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36  * SUCH DAMAGE.
37  */
38 
39 #if defined(LIBC_SCCS) && !defined(lint)
40 static char sccsid[] = "@(#)bt_split.c	8.10 (Berkeley) 1/9/95";
41 #endif /* LIBC_SCCS and not lint */
42 
43 #include <sys/types.h>
44 
45 #include <limits.h>
46 #include <stdio.h>
47 #include <stdlib.h>
48 #include <string.h>
49 
50 #include "db-int.h"
51 #include "btree.h"
52 
53 static int	 bt_broot __P((BTREE *, PAGE *, PAGE *, PAGE *));
54 static PAGE	*bt_page
55 		    __P((BTREE *, PAGE *, PAGE **, PAGE **, indx_t *, size_t));
56 static int	 bt_preserve __P((BTREE *, db_pgno_t));
57 static PAGE	*bt_psplit
58 		    __P((BTREE *, PAGE *, PAGE *, PAGE *, indx_t *, size_t));
59 static PAGE	*bt_root
60 		    __P((BTREE *, PAGE *, PAGE **, PAGE **, indx_t *, size_t));
61 static int	 bt_rroot __P((BTREE *, PAGE *, PAGE *, PAGE *));
62 static recno_t	 rec_total __P((PAGE *));
63 
64 #ifdef STATISTICS
65 u_long	bt_rootsplit, bt_split, bt_sortsplit, bt_pfxsaved;
66 #endif
67 
68 /*
69  * __BT_SPLIT -- Split the tree.
70  *
71  * Parameters:
72  *	t:	tree
73  *	sp:	page to split
74  *	key:	key to insert
75  *	data:	data to insert
76  *	flags:	BIGKEY/BIGDATA flags
77  *	ilen:	insert length
78  *	skip:	index to leave open
79  *
80  * Returns:
81  *	RET_ERROR, RET_SUCCESS
82  */
83 int
__bt_split(t,sp,key,data,flags,ilen,argskip)84 __bt_split(t, sp, key, data, flags, ilen, argskip)
85 	BTREE *t;
86 	PAGE *sp;
87 	const DBT *key, *data;
88 	int flags;
89 	size_t ilen;
90 	u_int32_t argskip;
91 {
92 	BINTERNAL *bi;
93 	BLEAF *bl, *tbl;
94 	DBT a, b;
95 	EPGNO *parent;
96 	PAGE *h, *l, *r, *lchild, *rchild;
97 	indx_t nxtindex;
98 	u_int16_t skip;
99 	u_int32_t n, nbytes, nksize;
100 	int parentsplit;
101 	char *dest;
102 
103 	/*
104 	 * Split the page into two pages, l and r.  The split routines return
105 	 * a pointer to the page into which the key should be inserted and with
106 	 * skip set to the offset which should be used.  Additionally, l and r
107 	 * are pinned.
108 	 */
109 	skip = argskip;
110 	h = sp->pgno == P_ROOT ?
111 	    bt_root(t, sp, &l, &r, &skip, ilen) :
112 	    bt_page(t, sp, &l, &r, &skip, ilen);
113 	if (h == NULL)
114 		return (RET_ERROR);
115 
116 	/*
117 	 * Insert the new key/data pair into the leaf page.  (Key inserts
118 	 * always cause a leaf page to split first.)
119 	 */
120 	h->linp[skip] = h->upper -= ilen;
121 	dest = (char *)h + h->upper;
122 	if (F_ISSET(t, R_RECNO))
123 		WR_RLEAF(dest, data, flags)
124 	else
125 		WR_BLEAF(dest, key, data, flags)
126 
127 	/* If the root page was split, make it look right. */
128 	if (sp->pgno == P_ROOT &&
129 	    (F_ISSET(t, R_RECNO) ?
130 	    bt_rroot(t, sp, l, r) : bt_broot(t, sp, l, r)) == RET_ERROR)
131 		goto err2;
132 
133 	/*
134 	 * Now we walk the parent page stack -- a LIFO stack of the pages that
135 	 * were traversed when we searched for the page that split.  Each stack
136 	 * entry is a page number and a page index offset.  The offset is for
137 	 * the page traversed on the search.  We've just split a page, so we
138 	 * have to insert a new key into the parent page.
139 	 *
140 	 * If the insert into the parent page causes it to split, may have to
141 	 * continue splitting all the way up the tree.  We stop if the root
142 	 * splits or the page inserted into didn't have to split to hold the
143 	 * new key.  Some algorithms replace the key for the old page as well
144 	 * as the new page.  We don't, as there's no reason to believe that the
145 	 * first key on the old page is any better than the key we have, and,
146 	 * in the case of a key being placed at index 0 causing the split, the
147 	 * key is unavailable.
148 	 *
149 	 * There are a maximum of 5 pages pinned at any time.  We keep the left
150 	 * and right pages pinned while working on the parent.   The 5 are the
151 	 * two children, left parent and right parent (when the parent splits)
152 	 * and the root page or the overflow key page when calling bt_preserve.
153 	 * This code must make sure that all pins are released other than the
154 	 * root page or overflow page which is unlocked elsewhere.
155 	 */
156 	while ((parent = BT_POP(t)) != NULL) {
157 		lchild = l;
158 		rchild = r;
159 
160 		/* Get the parent page. */
161 		if ((h = mpool_get(t->bt_mp, parent->pgno, 0)) == NULL)
162 			goto err2;
163 
164 	 	/*
165 		 * The new key goes ONE AFTER the index, because the split
166 		 * was to the right.
167 		 */
168 		skip = parent->index + 1;
169 
170 		/*
171 		 * Calculate the space needed on the parent page.
172 		 *
173 		 * Prefix trees: space hack when inserting into BINTERNAL
174 		 * pages.  Retain only what's needed to distinguish between
175 		 * the new entry and the LAST entry on the page to its left.
176 		 * If the keys compare equal, retain the entire key.  Note,
177 		 * we don't touch overflow keys, and the entire key must be
178 		 * retained for the next-to-left most key on the leftmost
179 		 * page of each level, or the search will fail.  Applicable
180 		 * ONLY to internal pages that have leaf pages as children.
181 		 * Further reduction of the key between pairs of internal
182 		 * pages loses too much information.
183 		 */
184 		switch (rchild->flags & P_TYPE) {
185 		case P_BINTERNAL:
186 			bi = GETBINTERNAL(rchild, 0);
187 			nbytes = NBINTERNAL(bi->ksize);
188 			break;
189 		case P_BLEAF:
190 			bl = GETBLEAF(rchild, 0);
191 			nbytes = NBINTERNAL(bl->ksize);
192 			if (t->bt_pfx && !(bl->flags & P_BIGKEY) &&
193 			    (h->prevpg != P_INVALID || skip > 1)) {
194 				tbl = GETBLEAF(lchild, NEXTINDEX(lchild) - 1);
195 				a.size = tbl->ksize;
196 				a.data = tbl->bytes;
197 				b.size = bl->ksize;
198 				b.data = bl->bytes;
199 				nksize = t->bt_pfx(&a, &b);
200 				n = NBINTERNAL(nksize);
201 				if (n < nbytes) {
202 #ifdef STATISTICS
203 					bt_pfxsaved += nbytes - n;
204 #endif
205 					nbytes = n;
206 				} else
207 					nksize = 0;
208 			} else
209 				nksize = 0;
210 			break;
211 		case P_RINTERNAL:
212 		case P_RLEAF:
213 			nbytes = NRINTERNAL;
214 			break;
215 		default:
216 			abort();
217 		}
218 
219 		/* Split the parent page if necessary or shift the indices. */
220 		if (h->upper - h->lower < nbytes + sizeof(indx_t)) {
221 			sp = h;
222 			h = h->pgno == P_ROOT ?
223 			    bt_root(t, h, &l, &r, &skip, nbytes) :
224 			    bt_page(t, h, &l, &r, &skip, nbytes);
225 			if (h == NULL)
226 				goto err1;
227 			parentsplit = 1;
228 		} else {
229 			if (skip < (nxtindex = NEXTINDEX(h)))
230 				memmove(h->linp + skip + 1, h->linp + skip,
231 				    (nxtindex - skip) * sizeof(indx_t));
232 			h->lower += sizeof(indx_t);
233 			parentsplit = 0;
234 		}
235 
236 		/* Insert the key into the parent page. */
237 		switch (rchild->flags & P_TYPE) {
238 		case P_BINTERNAL:
239 			h->linp[skip] = h->upper -= nbytes;
240 			dest = (char *)h + h->linp[skip];
241 			memmove(dest, bi, nbytes);
242 			((BINTERNAL *)dest)->pgno = rchild->pgno;
243 			break;
244 		case P_BLEAF:
245 			h->linp[skip] = h->upper -= nbytes;
246 			dest = (char *)h + h->linp[skip];
247 			WR_BINTERNAL(dest, nksize ? nksize : bl->ksize,
248 			    rchild->pgno, bl->flags & P_BIGKEY);
249 			memmove(dest, bl->bytes, nksize ? nksize : bl->ksize);
250 			if (bl->flags & P_BIGKEY &&
251 			    bt_preserve(t, *(db_pgno_t *)bl->bytes) == RET_ERROR)
252 				goto err1;
253 			break;
254 		case P_RINTERNAL:
255 			/*
256 			 * Update the left page count.  If split
257 			 * added at index 0, fix the correct page.
258 			 */
259 			if (skip > 0)
260 				dest = (char *)h + h->linp[skip - 1];
261 			else
262 				dest = (char *)l + l->linp[NEXTINDEX(l) - 1];
263 			((RINTERNAL *)dest)->nrecs = rec_total(lchild);
264 			((RINTERNAL *)dest)->pgno = lchild->pgno;
265 
266 			/* Update the right page count. */
267 			h->linp[skip] = h->upper -= nbytes;
268 			dest = (char *)h + h->linp[skip];
269 			((RINTERNAL *)dest)->nrecs = rec_total(rchild);
270 			((RINTERNAL *)dest)->pgno = rchild->pgno;
271 			break;
272 		case P_RLEAF:
273 			/*
274 			 * Update the left page count.  If split
275 			 * added at index 0, fix the correct page.
276 			 */
277 			if (skip > 0)
278 				dest = (char *)h + h->linp[skip - 1];
279 			else
280 				dest = (char *)l + l->linp[NEXTINDEX(l) - 1];
281 			((RINTERNAL *)dest)->nrecs = NEXTINDEX(lchild);
282 			((RINTERNAL *)dest)->pgno = lchild->pgno;
283 
284 			/* Update the right page count. */
285 			h->linp[skip] = h->upper -= nbytes;
286 			dest = (char *)h + h->linp[skip];
287 			((RINTERNAL *)dest)->nrecs = NEXTINDEX(rchild);
288 			((RINTERNAL *)dest)->pgno = rchild->pgno;
289 			break;
290 		default:
291 			abort();
292 		}
293 
294 		/* Unpin the held pages. */
295 		if (!parentsplit) {
296 			mpool_put(t->bt_mp, h, MPOOL_DIRTY);
297 			break;
298 		}
299 
300 		/* If the root page was split, make it look right. */
301 		if (sp->pgno == P_ROOT &&
302 		    (F_ISSET(t, R_RECNO) ?
303 		    bt_rroot(t, sp, l, r) : bt_broot(t, sp, l, r)) == RET_ERROR)
304 			goto err1;
305 
306 		mpool_put(t->bt_mp, lchild, MPOOL_DIRTY);
307 		mpool_put(t->bt_mp, rchild, MPOOL_DIRTY);
308 	}
309 
310 	/* Unpin the held pages. */
311 	mpool_put(t->bt_mp, l, MPOOL_DIRTY);
312 	mpool_put(t->bt_mp, r, MPOOL_DIRTY);
313 
314 	/* Clear any pages left on the stack. */
315 	return (RET_SUCCESS);
316 
317 	/*
318 	 * If something fails in the above loop we were already walking back
319 	 * up the tree and the tree is now inconsistent.  Nothing much we can
320 	 * do about it but release any memory we're holding.
321 	 */
322 err1:	mpool_put(t->bt_mp, lchild, MPOOL_DIRTY);
323 	mpool_put(t->bt_mp, rchild, MPOOL_DIRTY);
324 
325 err2:	mpool_put(t->bt_mp, l, 0);
326 	mpool_put(t->bt_mp, r, 0);
327 	__dbpanic(t->bt_dbp);
328 	return (RET_ERROR);
329 }
330 
331 /*
332  * BT_PAGE -- Split a non-root page of a btree.
333  *
334  * Parameters:
335  *	t:	tree
336  *	h:	root page
337  *	lp:	pointer to left page pointer
338  *	rp:	pointer to right page pointer
339  *	skip:	pointer to index to leave open
340  *	ilen:	insert length
341  *
342  * Returns:
343  *	Pointer to page in which to insert or NULL on error.
344  */
345 static PAGE *
bt_page(t,h,lp,rp,skip,ilen)346 bt_page(t, h, lp, rp, skip, ilen)
347 	BTREE *t;
348 	PAGE *h, **lp, **rp;
349 	indx_t *skip;
350 	size_t ilen;
351 {
352 	PAGE *l, *r, *tp;
353 	db_pgno_t npg;
354 
355 #ifdef STATISTICS
356 	++bt_split;
357 #endif
358 	/* Put the new right page for the split into place. */
359 	if ((r = __bt_new(t, &npg)) == NULL)
360 		return (NULL);
361 	r->pgno = npg;
362 	r->lower = BTDATAOFF;
363 	r->upper = t->bt_psize;
364 	r->nextpg = h->nextpg;
365 	r->prevpg = h->pgno;
366 	r->flags = h->flags & P_TYPE;
367 
368 	/*
369 	 * If we're splitting the last page on a level because we're appending
370 	 * a key to it (skip is NEXTINDEX()), it's likely that the data is
371 	 * sorted.  Adding an empty page on the side of the level is less work
372 	 * and can push the fill factor much higher than normal.  If we're
373 	 * wrong it's no big deal, we'll just do the split the right way next
374 	 * time.  It may look like it's equally easy to do a similar hack for
375 	 * reverse sorted data, that is, split the tree left, but it's not.
376 	 * Don't even try.
377 	 */
378 	if (h->nextpg == P_INVALID && *skip == NEXTINDEX(h)) {
379 #ifdef STATISTICS
380 		++bt_sortsplit;
381 #endif
382 		h->nextpg = r->pgno;
383 		r->lower = BTDATAOFF + sizeof(indx_t);
384 		*skip = 0;
385 		*lp = h;
386 		*rp = r;
387 		return (r);
388 	}
389 
390 	/* Put the new left page for the split into place. */
391 	if ((l = (PAGE *)malloc(t->bt_psize)) == NULL) {
392 		mpool_put(t->bt_mp, r, 0);
393 		return (NULL);
394 	}
395 #ifdef PURIFY
396 	memset(l, 0xff, t->bt_psize);
397 #endif
398 	l->pgno = h->pgno;
399 	l->nextpg = r->pgno;
400 	l->prevpg = h->prevpg;
401 	l->lower = BTDATAOFF;
402 	l->upper = t->bt_psize;
403 	l->flags = h->flags & P_TYPE;
404 
405 	/* Fix up the previous pointer of the page after the split page. */
406 	if (h->nextpg != P_INVALID) {
407 		if ((tp = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL) {
408 			free(l);
409 			/* XXX mpool_free(t->bt_mp, r->pgno); */
410 			return (NULL);
411 		}
412 		tp->prevpg = r->pgno;
413 		mpool_put(t->bt_mp, tp, MPOOL_DIRTY);
414 	}
415 
416 	/*
417 	 * Split right.  The key/data pairs aren't sorted in the btree page so
418 	 * it's simpler to copy the data from the split page onto two new pages
419 	 * instead of copying half the data to the right page and compacting
420 	 * the left page in place.  Since the left page can't change, we have
421 	 * to swap the original and the allocated left page after the split.
422 	 */
423 	tp = bt_psplit(t, h, l, r, skip, ilen);
424 
425 	/* Move the new left page onto the old left page. */
426 	memmove(h, l, t->bt_psize);
427 	if (tp == l)
428 		tp = h;
429 	free(l);
430 
431 	*lp = h;
432 	*rp = r;
433 	return (tp);
434 }
435 
436 /*
437  * BT_ROOT -- Split the root page of a btree.
438  *
439  * Parameters:
440  *	t:	tree
441  *	h:	root page
442  *	lp:	pointer to left page pointer
443  *	rp:	pointer to right page pointer
444  *	skip:	pointer to index to leave open
445  *	ilen:	insert length
446  *
447  * Returns:
448  *	Pointer to page in which to insert or NULL on error.
449  */
450 static PAGE *
bt_root(t,h,lp,rp,skip,ilen)451 bt_root(t, h, lp, rp, skip, ilen)
452 	BTREE *t;
453 	PAGE *h, **lp, **rp;
454 	indx_t *skip;
455 	size_t ilen;
456 {
457 	PAGE *l, *r, *tp;
458 	db_pgno_t lnpg, rnpg;
459 
460 #ifdef STATISTICS
461 	++bt_split;
462 	++bt_rootsplit;
463 #endif
464 	/* Put the new left and right pages for the split into place. */
465 	if ((l = __bt_new(t, &lnpg)) == NULL ||
466 	    (r = __bt_new(t, &rnpg)) == NULL)
467 		return (NULL);
468 	l->pgno = lnpg;
469 	r->pgno = rnpg;
470 	l->nextpg = r->pgno;
471 	r->prevpg = l->pgno;
472 	l->prevpg = r->nextpg = P_INVALID;
473 	l->lower = r->lower = BTDATAOFF;
474 	l->upper = r->upper = t->bt_psize;
475 	l->flags = r->flags = h->flags & P_TYPE;
476 
477 	/* Split the root page. */
478 	tp = bt_psplit(t, h, l, r, skip, ilen);
479 
480 	*lp = l;
481 	*rp = r;
482 	return (tp);
483 }
484 
485 /*
486  * BT_RROOT -- Fix up the recno root page after it has been split.
487  *
488  * Parameters:
489  *	t:	tree
490  *	h:	root page
491  *	l:	left page
492  *	r:	right page
493  *
494  * Returns:
495  *	RET_ERROR, RET_SUCCESS
496  */
497 static int
bt_rroot(t,h,l,r)498 bt_rroot(t, h, l, r)
499 	BTREE *t;
500 	PAGE *h, *l, *r;
501 {
502 	char *dest;
503 
504 	/* Insert the left and right keys, set the header information. */
505 	h->linp[0] = h->upper = t->bt_psize - NRINTERNAL;
506 	dest = (char *)h + h->upper;
507 	WR_RINTERNAL(dest,
508 	    l->flags & P_RLEAF ? NEXTINDEX(l) : rec_total(l), l->pgno);
509 
510 	h->linp[1] = h->upper -= NRINTERNAL;
511 	dest = (char *)h + h->upper;
512 	WR_RINTERNAL(dest,
513 	    r->flags & P_RLEAF ? NEXTINDEX(r) : rec_total(r), r->pgno);
514 
515 	h->lower = BTDATAOFF + 2 * sizeof(indx_t);
516 
517 	/* Unpin the root page, set to recno internal page. */
518 	h->flags &= ~P_TYPE;
519 	h->flags |= P_RINTERNAL;
520 	mpool_put(t->bt_mp, h, MPOOL_DIRTY);
521 
522 	return (RET_SUCCESS);
523 }
524 
525 /*
526  * BT_BROOT -- Fix up the btree root page after it has been split.
527  *
528  * Parameters:
529  *	t:	tree
530  *	h:	root page
531  *	l:	left page
532  *	r:	right page
533  *
534  * Returns:
535  *	RET_ERROR, RET_SUCCESS
536  */
537 static int
bt_broot(t,h,l,r)538 bt_broot(t, h, l, r)
539 	BTREE *t;
540 	PAGE *h, *l, *r;
541 {
542 	BINTERNAL *bi;
543 	BLEAF *bl;
544 	u_int32_t nbytes;
545 	char *dest;
546 
547 	/*
548 	 * If the root page was a leaf page, change it into an internal page.
549 	 * We copy the key we split on (but not the key's data, in the case of
550 	 * a leaf page) to the new root page.
551 	 *
552 	 * The btree comparison code guarantees that the left-most key on any
553 	 * level of the tree is never used, so it doesn't need to be filled in.
554 	 */
555 	nbytes = NBINTERNAL(0);
556 	h->linp[0] = h->upper = t->bt_psize - nbytes;
557 	dest = (char *)h + h->upper;
558 	WR_BINTERNAL(dest, 0, l->pgno, 0);
559 
560 	switch (h->flags & P_TYPE) {
561 	case P_BLEAF:
562 		bl = GETBLEAF(r, 0);
563 		nbytes = NBINTERNAL(bl->ksize);
564 		h->linp[1] = h->upper -= nbytes;
565 		dest = (char *)h + h->upper;
566 		WR_BINTERNAL(dest, bl->ksize, r->pgno, 0);
567 		memmove(dest, bl->bytes, bl->ksize);
568 
569 		/*
570 		 * If the key is on an overflow page, mark the overflow chain
571 		 * so it isn't deleted when the leaf copy of the key is deleted.
572 		 */
573 		if (bl->flags & P_BIGKEY &&
574 		    bt_preserve(t, *(db_pgno_t *)bl->bytes) == RET_ERROR)
575 			return (RET_ERROR);
576 		break;
577 	case P_BINTERNAL:
578 		bi = GETBINTERNAL(r, 0);
579 		nbytes = NBINTERNAL(bi->ksize);
580 		h->linp[1] = h->upper -= nbytes;
581 		dest = (char *)h + h->upper;
582 		memmove(dest, bi, nbytes);
583 		((BINTERNAL *)dest)->pgno = r->pgno;
584 		break;
585 	default:
586 		abort();
587 	}
588 
589 	/* There are two keys on the page. */
590 	h->lower = BTDATAOFF + 2 * sizeof(indx_t);
591 
592 	/* Unpin the root page, set to btree internal page. */
593 	h->flags &= ~P_TYPE;
594 	h->flags |= P_BINTERNAL;
595 	mpool_put(t->bt_mp, h, MPOOL_DIRTY);
596 
597 	return (RET_SUCCESS);
598 }
599 
600 /*
601  * BT_PSPLIT -- Do the real work of splitting the page.
602  *
603  * Parameters:
604  *	t:	tree
605  *	h:	page to be split
606  *	l:	page to put lower half of data
607  *	r:	page to put upper half of data
608  *	pskip:	pointer to index to leave open
609  *	ilen:	insert length
610  *
611  * Returns:
612  *	Pointer to page in which to insert.
613  */
614 static PAGE *
bt_psplit(t,h,l,r,pskip,ilen)615 bt_psplit(t, h, l, r, pskip, ilen)
616 	BTREE *t;
617 	PAGE *h, *l, *r;
618 	indx_t *pskip;
619 	size_t ilen;
620 {
621 	BINTERNAL *bi;
622 	BLEAF *bl;
623 	CURSOR *c;
624 	RLEAF *rl;
625 	PAGE *rval;
626 	void *src;
627 	indx_t full, half, nxt, off, skip, top, used;
628 	u_int32_t nbytes;
629 	int bigkeycnt, isbigkey;
630 
631 	/*
632 	 * Split the data to the left and right pages.  Leave the skip index
633 	 * open.  Additionally, make some effort not to split on an overflow
634 	 * key.  This makes internal page processing faster and can save
635 	 * space as overflow keys used by internal pages are never deleted.
636 	 */
637 	bigkeycnt = 0;
638 	skip = *pskip;
639 	full = t->bt_psize - BTDATAOFF;
640 	half = full / 2;
641 	used = 0;
642 	for (nxt = off = 0, top = NEXTINDEX(h); nxt < top; ++off) {
643 		if (skip == off) {
644 			nbytes = ilen;
645 			isbigkey = 0;		/* XXX: not really known. */
646 		} else
647 			switch (h->flags & P_TYPE) {
648 			case P_BINTERNAL:
649 				src = bi = GETBINTERNAL(h, nxt);
650 				nbytes = NBINTERNAL(bi->ksize);
651 				isbigkey = bi->flags & P_BIGKEY;
652 				break;
653 			case P_BLEAF:
654 				src = bl = GETBLEAF(h, nxt);
655 				nbytes = NBLEAF(bl);
656 				isbigkey = bl->flags & P_BIGKEY;
657 				break;
658 			case P_RINTERNAL:
659 				src = GETRINTERNAL(h, nxt);
660 				nbytes = NRINTERNAL;
661 				isbigkey = 0;
662 				break;
663 			case P_RLEAF:
664 				src = rl = GETRLEAF(h, nxt);
665 				nbytes = NRLEAF(rl);
666 				isbigkey = 0;
667 				break;
668 			default:
669 				abort();
670 			}
671 
672 		/*
673 		 * If the key/data pairs are substantial fractions of the max
674 		 * possible size for the page, it's possible to get situations
675 		 * where we decide to try and copy too much onto the left page.
676 		 * Make sure that doesn't happen.
677 		 */
678 		if ((skip <= off && used + nbytes + sizeof(indx_t) >= full)
679 		    || nxt == top - 1) {
680 			--off;
681 			break;
682 		}
683 
684 		/* Copy the key/data pair, if not the skipped index. */
685 		if (skip != off) {
686 			++nxt;
687 
688 			l->linp[off] = l->upper -= nbytes;
689 			memmove((char *)l + l->upper, src, nbytes);
690 		}
691 
692 		used += nbytes + sizeof(indx_t);
693 		if (used >= half) {
694 			if (!isbigkey || bigkeycnt == 3)
695 				break;
696 			else
697 				++bigkeycnt;
698 		}
699 	}
700 
701 	/*
702 	 * Off is the last offset that's valid for the left page.
703 	 * Nxt is the first offset to be placed on the right page.
704 	 */
705 	l->lower += (off + 1) * sizeof(indx_t);
706 
707 	/*
708 	 * If splitting the page that the cursor was on, the cursor has to be
709 	 * adjusted to point to the same record as before the split.  If the
710 	 * cursor is at or past the skipped slot, the cursor is incremented by
711 	 * one.  If the cursor is on the right page, it is decremented by the
712 	 * number of records split to the left page.
713 	 */
714 	c = &t->bt_cursor;
715 	if (F_ISSET(c, CURS_INIT) && c->pg.pgno == h->pgno) {
716 		if (c->pg.index >= skip)
717 			++c->pg.index;
718 		if (c->pg.index < nxt)			/* Left page. */
719 			c->pg.pgno = l->pgno;
720 		else {					/* Right page. */
721 			c->pg.pgno = r->pgno;
722 			c->pg.index -= nxt;
723 		}
724 	}
725 
726 	/*
727 	 * If the skipped index was on the left page, just return that page.
728 	 * Otherwise, adjust the skip index to reflect the new position on
729 	 * the right page.
730 	 */
731 	if (skip <= off) {
732 		/*
733 		 * If we get here then 'skip' is in the left page.  We do
734 		 * not want to mix this with the right page, so we assign
735 		 * an unrealistic value (-1).
736 		 */
737 		skip = (indx_t)-1;
738 		rval = l;
739 	} else {
740 		rval = r;
741 		*pskip -= nxt;
742 	}
743 
744 	for (off = 0; nxt < top; ++off) {
745 		if (skip == nxt) {
746 			++off;
747 			/*
748 			 * Assign 'skip' an unrealistic value (-1) to ensure
749 			 * it is not matched again.
750 			 */
751 			skip = (indx_t)-1;
752 		}
753 		switch (h->flags & P_TYPE) {
754 		case P_BINTERNAL:
755 			src = bi = GETBINTERNAL(h, nxt);
756 			nbytes = NBINTERNAL(bi->ksize);
757 			break;
758 		case P_BLEAF:
759 			src = bl = GETBLEAF(h, nxt);
760 			nbytes = NBLEAF(bl);
761 			break;
762 		case P_RINTERNAL:
763 			src = GETRINTERNAL(h, nxt);
764 			nbytes = NRINTERNAL;
765 			break;
766 		case P_RLEAF:
767 			src = rl = GETRLEAF(h, nxt);
768 			nbytes = NRLEAF(rl);
769 			break;
770 		default:
771 			abort();
772 		}
773 		++nxt;
774 		r->linp[off] = r->upper -= nbytes;
775 		memmove((char *)r + r->upper, src, nbytes);
776 	}
777 	r->lower += off * sizeof(indx_t);
778 
779 	/* If the key is being appended to the page, adjust the index. */
780 	if (skip == top)
781 		r->lower += sizeof(indx_t);
782 
783 	return (rval);
784 }
785 
786 /*
787  * BT_PRESERVE -- Mark a chain of pages as used by an internal node.
788  *
789  * Chains of indirect blocks pointed to by leaf nodes get reclaimed when the
790  * record that references them gets deleted.  Chains pointed to by internal
791  * pages never get deleted.  This routine marks a chain as pointed to by an
792  * internal page.
793  *
794  * Parameters:
795  *	t:	tree
796  *	pg:	page number of first page in the chain.
797  *
798  * Returns:
799  *	RET_SUCCESS, RET_ERROR.
800  */
801 static int
bt_preserve(t,pg)802 bt_preserve(t, pg)
803 	BTREE *t;
804 	db_pgno_t pg;
805 {
806 	PAGE *h;
807 
808 	if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
809 		return (RET_ERROR);
810 	h->flags |= P_PRESERVE;
811 	mpool_put(t->bt_mp, h, MPOOL_DIRTY);
812 	return (RET_SUCCESS);
813 }
814 
815 /*
816  * REC_TOTAL -- Return the number of recno entries below a page.
817  *
818  * Parameters:
819  *	h:	page
820  *
821  * Returns:
822  *	The number of recno entries below a page.
823  *
824  * XXX
825  * These values could be set by the bt_psplit routine.  The problem is that the
826  * entry has to be popped off of the stack etc. or the values have to be passed
827  * all the way back to bt_split/bt_rroot and it's not very clean.
828  */
829 static recno_t
rec_total(h)830 rec_total(h)
831 	PAGE *h;
832 {
833 	recno_t recs;
834 	indx_t nxt, top;
835 
836 	for (recs = 0, nxt = 0, top = NEXTINDEX(h); nxt < top; ++nxt)
837 		recs += GETRINTERNAL(h, nxt)->nrecs;
838 	return (recs);
839 }
840