2 * Copyright (c) 1990, 1993, 1994
3 * The Regents of the University of California. All rights reserved.
5 * This code is derived from software contributed to Berkeley by
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 * must display the following acknowledgement:
18 * This product includes software developed by the University of
19 * California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 * may be used to endorse or promote products derived from this software
22 * without specific prior written permission.
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 #if defined(LIBC_SCCS) && !defined(lint)
38 static char sccsid
[] = "@(#)bt_split.c 8.9 (Berkeley) 7/26/94";
39 #endif /* LIBC_SCCS and not lint */
41 #include <sys/types.h>
51 static int bt_broot
__P((BTREE
*, PAGE
*, PAGE
*, PAGE
*));
53 __P((BTREE
*, PAGE
*, PAGE
**, PAGE
**, indx_t
*, size_t));
54 static int bt_preserve
__P((BTREE
*, pgno_t
));
55 static PAGE
*bt_psplit
56 __P((BTREE
*, PAGE
*, PAGE
*, PAGE
*, indx_t
*, size_t));
58 __P((BTREE
*, PAGE
*, PAGE
**, PAGE
**, indx_t
*, size_t));
59 static int bt_rroot
__P((BTREE
*, PAGE
*, PAGE
*, PAGE
*));
60 static recno_t rec_total
__P((PAGE
*));
63 u_long bt_rootsplit
, bt_split
, bt_sortsplit
, bt_pfxsaved
;
67 * __BT_SPLIT -- Split the tree.
73 * data: data to insert
74 * flags: BIGKEY/BIGDATA flags
76 * skip: index to leave open
79 * RET_ERROR, RET_SUCCESS
82 __bt_split(t
, sp
, key
, data
, flags
, ilen
, argskip
)
85 const DBT
*key
, *data
;
94 PAGE
*h
, *l
, *r
, *lchild
, *rchild
;
97 u_int32_t n
, nbytes
, nksize
;
102 * Split the page into two pages, l and r. The split routines return
103 * a pointer to the page into which the key should be inserted and with
104 * skip set to the offset which should be used. Additionally, l and r
108 h
= sp
->pgno
== P_ROOT
?
109 bt_root(t
, sp
, &l
, &r
, &skip
, ilen
) :
110 bt_page(t
, sp
, &l
, &r
, &skip
, ilen
);
115 * Insert the new key/data pair into the leaf page. (Key inserts
116 * always cause a leaf page to split first.)
118 h
->linp
[skip
] = h
->upper
-= ilen
;
119 dest
= (char *)h
+ h
->upper
;
120 if (F_ISSET(t
, R_RECNO
))
121 WR_RLEAF(dest
, data
, flags
)
123 WR_BLEAF(dest
, key
, data
, flags
)
125 /* If the root page was split, make it look right. */
126 if (sp
->pgno
== P_ROOT
&&
127 (F_ISSET(t
, R_RECNO
) ?
128 bt_rroot(t
, sp
, l
, r
) : bt_broot(t
, sp
, l
, r
)) == RET_ERROR
)
132 * Now we walk the parent page stack -- a LIFO stack of the pages that
133 * were traversed when we searched for the page that split. Each stack
134 * entry is a page number and a page index offset. The offset is for
135 * the page traversed on the search. We've just split a page, so we
136 * have to insert a new key into the parent page.
138 * If the insert into the parent page causes it to split, may have to
139 * continue splitting all the way up the tree. We stop if the root
140 * splits or the page inserted into didn't have to split to hold the
141 * new key. Some algorithms replace the key for the old page as well
142 * as the new page. We don't, as there's no reason to believe that the
143 * first key on the old page is any better than the key we have, and,
144 * in the case of a key being placed at index 0 causing the split, the
145 * key is unavailable.
147 * There are a maximum of 5 pages pinned at any time. We keep the left
148 * and right pages pinned while working on the parent. The 5 are the
149 * two children, left parent and right parent (when the parent splits)
150 * and the root page or the overflow key page when calling bt_preserve.
151 * This code must make sure that all pins are released other than the
152 * root page or overflow page which is unlocked elsewhere.
154 while ((parent
= BT_POP(t
)) != NULL
) {
158 /* Get the parent page. */
159 if ((h
= mpool_get(t
->bt_mp
, parent
->pgno
, 0)) == NULL
)
163 * The new key goes ONE AFTER the index, because the split
166 skip
= parent
->index
+ 1;
169 * Calculate the space needed on the parent page.
171 * Prefix trees: space hack when inserting into BINTERNAL
172 * pages. Retain only what's needed to distinguish between
173 * the new entry and the LAST entry on the page to its left.
174 * If the keys compare equal, retain the entire key. Note,
175 * we don't touch overflow keys, and the entire key must be
176 * retained for the next-to-left most key on the leftmost
177 * page of each level, or the search will fail. Applicable
178 * ONLY to internal pages that have leaf pages as children.
179 * Further reduction of the key between pairs of internal
180 * pages loses too much information.
182 switch (rchild
->flags
& P_TYPE
) {
184 bi
= GETBINTERNAL(rchild
, 0);
185 nbytes
= NBINTERNAL(bi
->ksize
);
188 bl
= GETBLEAF(rchild
, 0);
189 nbytes
= NBINTERNAL(bl
->ksize
);
190 if (t
->bt_pfx
&& !(bl
->flags
& P_BIGKEY
) &&
191 (h
->prevpg
!= P_INVALID
|| skip
> 1)) {
192 tbl
= GETBLEAF(lchild
, NEXTINDEX(lchild
) - 1);
197 nksize
= t
->bt_pfx(&a
, &b
);
198 n
= NBINTERNAL(nksize
);
201 bt_pfxsaved
+= nbytes
- n
;
217 /* Split the parent page if necessary or shift the indices. */
218 if (h
->upper
- h
->lower
< nbytes
+ sizeof(indx_t
)) {
220 h
= h
->pgno
== P_ROOT
?
221 bt_root(t
, h
, &l
, &r
, &skip
, nbytes
) :
222 bt_page(t
, h
, &l
, &r
, &skip
, nbytes
);
227 if (skip
< (nxtindex
= NEXTINDEX(h
)))
228 memmove(h
->linp
+ skip
+ 1, h
->linp
+ skip
,
229 (nxtindex
- skip
) * sizeof(indx_t
));
230 h
->lower
+= sizeof(indx_t
);
234 /* Insert the key into the parent page. */
235 switch (rchild
->flags
& P_TYPE
) {
237 h
->linp
[skip
] = h
->upper
-= nbytes
;
238 dest
= (char *)h
+ h
->linp
[skip
];
239 memmove(dest
, bi
, nbytes
);
240 ((BINTERNAL
*)dest
)->pgno
= rchild
->pgno
;
243 h
->linp
[skip
] = h
->upper
-= nbytes
;
244 dest
= (char *)h
+ h
->linp
[skip
];
245 WR_BINTERNAL(dest
, nksize
? nksize
: bl
->ksize
,
246 rchild
->pgno
, bl
->flags
& P_BIGKEY
);
247 memmove(dest
, bl
->bytes
, nksize
? nksize
: bl
->ksize
);
248 if (bl
->flags
& P_BIGKEY
&&
249 bt_preserve(t
, *(pgno_t
*)bl
->bytes
) == RET_ERROR
)
254 * Update the left page count. If split
255 * added at index 0, fix the correct page.
258 dest
= (char *)h
+ h
->linp
[skip
- 1];
260 dest
= (char *)l
+ l
->linp
[NEXTINDEX(l
) - 1];
261 ((RINTERNAL
*)dest
)->nrecs
= rec_total(lchild
);
262 ((RINTERNAL
*)dest
)->pgno
= lchild
->pgno
;
264 /* Update the right page count. */
265 h
->linp
[skip
] = h
->upper
-= nbytes
;
266 dest
= (char *)h
+ h
->linp
[skip
];
267 ((RINTERNAL
*)dest
)->nrecs
= rec_total(rchild
);
268 ((RINTERNAL
*)dest
)->pgno
= rchild
->pgno
;
272 * Update the left page count. If split
273 * added at index 0, fix the correct page.
276 dest
= (char *)h
+ h
->linp
[skip
- 1];
278 dest
= (char *)l
+ l
->linp
[NEXTINDEX(l
) - 1];
279 ((RINTERNAL
*)dest
)->nrecs
= NEXTINDEX(lchild
);
280 ((RINTERNAL
*)dest
)->pgno
= lchild
->pgno
;
282 /* Update the right page count. */
283 h
->linp
[skip
] = h
->upper
-= nbytes
;
284 dest
= (char *)h
+ h
->linp
[skip
];
285 ((RINTERNAL
*)dest
)->nrecs
= NEXTINDEX(rchild
);
286 ((RINTERNAL
*)dest
)->pgno
= rchild
->pgno
;
292 /* Unpin the held pages. */
294 mpool_put(t
->bt_mp
, h
, MPOOL_DIRTY
);
298 /* If the root page was split, make it look right. */
299 if (sp
->pgno
== P_ROOT
&&
300 (F_ISSET(t
, R_RECNO
) ?
301 bt_rroot(t
, sp
, l
, r
) : bt_broot(t
, sp
, l
, r
)) == RET_ERROR
)
304 mpool_put(t
->bt_mp
, lchild
, MPOOL_DIRTY
);
305 mpool_put(t
->bt_mp
, rchild
, MPOOL_DIRTY
);
308 /* Unpin the held pages. */
309 mpool_put(t
->bt_mp
, l
, MPOOL_DIRTY
);
310 mpool_put(t
->bt_mp
, r
, MPOOL_DIRTY
);
312 /* Clear any pages left on the stack. */
313 return (RET_SUCCESS
);
316 * If something fails in the above loop we were already walking back
317 * up the tree and the tree is now inconsistent. Nothing much we can
318 * do about it but release any memory we're holding.
320 err1
: mpool_put(t
->bt_mp
, lchild
, MPOOL_DIRTY
);
321 mpool_put(t
->bt_mp
, rchild
, MPOOL_DIRTY
);
323 err2
: mpool_put(t
->bt_mp
, l
, 0);
324 mpool_put(t
->bt_mp
, r
, 0);
325 __dbpanic(t
->bt_dbp
);
330 * BT_PAGE -- Split a non-root page of a btree.
335 * lp: pointer to left page pointer
336 * rp: pointer to right page pointer
337 * skip: pointer to index to leave open
338 * ilen: insert length
341 * Pointer to page in which to insert or NULL on error.
344 bt_page(t
, h
, lp
, rp
, skip
, ilen
)
356 /* Put the new right page for the split into place. */
357 if ((r
= __bt_new(t
, &npg
)) == NULL
)
360 r
->lower
= BTDATAOFF
;
361 r
->upper
= t
->bt_psize
;
362 r
->nextpg
= h
->nextpg
;
364 r
->flags
= h
->flags
& P_TYPE
;
367 * If we're splitting the last page on a level because we're appending
368 * a key to it (skip is NEXTINDEX()), it's likely that the data is
369 * sorted. Adding an empty page on the side of the level is less work
370 * and can push the fill factor much higher than normal. If we're
371 * wrong it's no big deal, we'll just do the split the right way next
372 * time. It may look like it's equally easy to do a similar hack for
373 * reverse sorted data, that is, split the tree left, but it's not.
376 if (h
->nextpg
== P_INVALID
&& *skip
== NEXTINDEX(h
)) {
381 r
->lower
= BTDATAOFF
+ sizeof(indx_t
);
388 /* Put the new left page for the split into place. */
389 if ((l
= (PAGE
*)malloc(t
->bt_psize
)) == NULL
) {
390 mpool_put(t
->bt_mp
, r
, 0);
394 memset(l
, 0xff, t
->bt_psize
);
398 l
->prevpg
= h
->prevpg
;
399 l
->lower
= BTDATAOFF
;
400 l
->upper
= t
->bt_psize
;
401 l
->flags
= h
->flags
& P_TYPE
;
403 /* Fix up the previous pointer of the page after the split page. */
404 if (h
->nextpg
!= P_INVALID
) {
405 if ((tp
= mpool_get(t
->bt_mp
, h
->nextpg
, 0)) == NULL
) {
407 /* XXX mpool_free(t->bt_mp, r->pgno); */
410 tp
->prevpg
= r
->pgno
;
411 mpool_put(t
->bt_mp
, tp
, MPOOL_DIRTY
);
415 * Split right. The key/data pairs aren't sorted in the btree page so
416 * it's simpler to copy the data from the split page onto two new pages
417 * instead of copying half the data to the right page and compacting
418 * the left page in place. Since the left page can't change, we have
419 * to swap the original and the allocated left page after the split.
421 tp
= bt_psplit(t
, h
, l
, r
, skip
, ilen
);
423 /* Move the new left page onto the old left page. */
424 memmove(h
, l
, t
->bt_psize
);
435 * BT_ROOT -- Split the root page of a btree.
440 * lp: pointer to left page pointer
441 * rp: pointer to right page pointer
442 * skip: pointer to index to leave open
443 * ilen: insert length
446 * Pointer to page in which to insert or NULL on error.
449 bt_root(t
, h
, lp
, rp
, skip
, ilen
)
462 /* Put the new left and right pages for the split into place. */
463 if ((l
= __bt_new(t
, &lnpg
)) == NULL
||
464 (r
= __bt_new(t
, &rnpg
)) == NULL
)
470 l
->prevpg
= r
->nextpg
= P_INVALID
;
471 l
->lower
= r
->lower
= BTDATAOFF
;
472 l
->upper
= r
->upper
= t
->bt_psize
;
473 l
->flags
= r
->flags
= h
->flags
& P_TYPE
;
475 /* Split the root page. */
476 tp
= bt_psplit(t
, h
, l
, r
, skip
, ilen
);
484 * BT_RROOT -- Fix up the recno root page after it has been split.
493 * RET_ERROR, RET_SUCCESS
502 /* Insert the left and right keys, set the header information. */
503 h
->linp
[0] = h
->upper
= t
->bt_psize
- NRINTERNAL
;
504 dest
= (char *)h
+ h
->upper
;
506 l
->flags
& P_RLEAF
? NEXTINDEX(l
) : rec_total(l
), l
->pgno
);
508 h
->linp
[1] = h
->upper
-= NRINTERNAL
;
509 dest
= (char *)h
+ h
->upper
;
511 r
->flags
& P_RLEAF
? NEXTINDEX(r
) : rec_total(r
), r
->pgno
);
513 h
->lower
= BTDATAOFF
+ 2 * sizeof(indx_t
);
515 /* Unpin the root page, set to recno internal page. */
517 h
->flags
|= P_RINTERNAL
;
518 mpool_put(t
->bt_mp
, h
, MPOOL_DIRTY
);
520 return (RET_SUCCESS
);
524 * BT_BROOT -- Fix up the btree root page after it has been split.
533 * RET_ERROR, RET_SUCCESS
546 * If the root page was a leaf page, change it into an internal page.
547 * We copy the key we split on (but not the key's data, in the case of
548 * a leaf page) to the new root page.
550 * The btree comparison code guarantees that the left-most key on any
551 * level of the tree is never used, so it doesn't need to be filled in.
553 nbytes
= NBINTERNAL(0);
554 h
->linp
[0] = h
->upper
= t
->bt_psize
- nbytes
;
555 dest
= (char *)h
+ h
->upper
;
556 WR_BINTERNAL(dest
, 0, l
->pgno
, 0);
558 switch (h
->flags
& P_TYPE
) {
561 nbytes
= NBINTERNAL(bl
->ksize
);
562 h
->linp
[1] = h
->upper
-= nbytes
;
563 dest
= (char *)h
+ h
->upper
;
564 WR_BINTERNAL(dest
, bl
->ksize
, r
->pgno
, 0);
565 memmove(dest
, bl
->bytes
, bl
->ksize
);
568 * If the key is on an overflow page, mark the overflow chain
569 * so it isn't deleted when the leaf copy of the key is deleted.
571 if (bl
->flags
& P_BIGKEY
&&
572 bt_preserve(t
, *(pgno_t
*)bl
->bytes
) == RET_ERROR
)
576 bi
= GETBINTERNAL(r
, 0);
577 nbytes
= NBINTERNAL(bi
->ksize
);
578 h
->linp
[1] = h
->upper
-= nbytes
;
579 dest
= (char *)h
+ h
->upper
;
580 memmove(dest
, bi
, nbytes
);
581 ((BINTERNAL
*)dest
)->pgno
= r
->pgno
;
587 /* There are two keys on the page. */
588 h
->lower
= BTDATAOFF
+ 2 * sizeof(indx_t
);
590 /* Unpin the root page, set to btree internal page. */
592 h
->flags
|= P_BINTERNAL
;
593 mpool_put(t
->bt_mp
, h
, MPOOL_DIRTY
);
595 return (RET_SUCCESS
);
599 * BT_PSPLIT -- Do the real work of splitting the page.
603 * h: page to be split
604 * l: page to put lower half of data
605 * r: page to put upper half of data
606 * pskip: pointer to index to leave open
607 * ilen: insert length
610 * Pointer to page in which to insert.
613 bt_psplit(t
, h
, l
, r
, pskip
, ilen
)
625 indx_t full
, half
, nxt
, off
, skip
, top
, used
;
627 int bigkeycnt
, isbigkey
;
630 * Split the data to the left and right pages. Leave the skip index
631 * open. Additionally, make some effort not to split on an overflow
632 * key. This makes internal page processing faster and can save
633 * space as overflow keys used by internal pages are never deleted.
637 full
= t
->bt_psize
- BTDATAOFF
;
640 for (nxt
= off
= 0, top
= NEXTINDEX(h
); nxt
< top
; ++off
) {
643 isbigkey
= 0; /* XXX: not really known. */
645 switch (h
->flags
& P_TYPE
) {
647 src
= bi
= GETBINTERNAL(h
, nxt
);
648 nbytes
= NBINTERNAL(bi
->ksize
);
649 isbigkey
= bi
->flags
& P_BIGKEY
;
652 src
= bl
= GETBLEAF(h
, nxt
);
654 isbigkey
= bl
->flags
& P_BIGKEY
;
657 src
= GETRINTERNAL(h
, nxt
);
662 src
= rl
= GETRLEAF(h
, nxt
);
671 * If the key/data pairs are substantial fractions of the max
672 * possible size for the page, it's possible to get situations
673 * where we decide to try and copy too much onto the left page.
674 * Make sure that doesn't happen.
676 if (skip
<= off
&& used
+ nbytes
>= full
) {
681 /* Copy the key/data pair, if not the skipped index. */
685 l
->linp
[off
] = l
->upper
-= nbytes
;
686 memmove((char *)l
+ l
->upper
, src
, nbytes
);
691 if (!isbigkey
|| bigkeycnt
== 3)
699 * Off is the last offset that's valid for the left page.
700 * Nxt is the first offset to be placed on the right page.
702 l
->lower
+= (off
+ 1) * sizeof(indx_t
);
705 * If splitting the page that the cursor was on, the cursor has to be
706 * adjusted to point to the same record as before the split. If the
707 * cursor is at or past the skipped slot, the cursor is incremented by
708 * one. If the cursor is on the right page, it is decremented by the
709 * number of records split to the left page.
712 if (F_ISSET(c
, CURS_INIT
) && c
->pg
.pgno
== h
->pgno
) {
713 if (c
->pg
.index
>= skip
)
715 if (c
->pg
.index
< nxt
) /* Left page. */
716 c
->pg
.pgno
= l
->pgno
;
717 else { /* Right page. */
718 c
->pg
.pgno
= r
->pgno
;
724 * If the skipped index was on the left page, just return that page.
725 * Otherwise, adjust the skip index to reflect the new position on
736 for (off
= 0; nxt
< top
; ++off
) {
741 switch (h
->flags
& P_TYPE
) {
743 src
= bi
= GETBINTERNAL(h
, nxt
);
744 nbytes
= NBINTERNAL(bi
->ksize
);
747 src
= bl
= GETBLEAF(h
, nxt
);
751 src
= GETRINTERNAL(h
, nxt
);
755 src
= rl
= GETRLEAF(h
, nxt
);
762 r
->linp
[off
] = r
->upper
-= nbytes
;
763 memmove((char *)r
+ r
->upper
, src
, nbytes
);
765 r
->lower
+= off
* sizeof(indx_t
);
767 /* If the key is being appended to the page, adjust the index. */
769 r
->lower
+= sizeof(indx_t
);
775 * BT_PRESERVE -- Mark a chain of pages as used by an internal node.
777 * Chains of indirect blocks pointed to by leaf nodes get reclaimed when the
778 * record that references them gets deleted. Chains pointed to by internal
779 * pages never get deleted. This routine marks a chain as pointed to by an
784 * pg: page number of first page in the chain.
787 * RET_SUCCESS, RET_ERROR.
796 if ((h
= mpool_get(t
->bt_mp
, pg
, 0)) == NULL
)
798 h
->flags
|= P_PRESERVE
;
799 mpool_put(t
->bt_mp
, h
, MPOOL_DIRTY
);
800 return (RET_SUCCESS
);
804 * REC_TOTAL -- Return the number of recno entries below a page.
810 * The number of recno entries below a page.
813 * These values could be set by the bt_psplit routine. The problem is that the
814 * entry has to be popped off of the stack etc. or the values have to be passed
815 * all the way back to bt_split/bt_rroot and it's not very clean.
824 for (recs
= 0, nxt
= 0, top
= NEXTINDEX(h
); nxt
< top
; ++nxt
)
825 recs
+= GETRINTERNAL(h
, nxt
)->nrecs
;