db/btree/bt_search.c

   1 /*
   2  * Copyright (c) 2003 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23 /*-
  24  * Copyright (c) 1990, 1993, 1994
  25  *      The Regents of the University of California.  All rights reserved.
  26  *
  27  * This code is derived from software contributed to Berkeley by
  28  * Mike Olson.
  29  *
  30  * Redistribution and use in source and binary forms, with or without
  31  * modification, are permitted provided that the following conditions
  32  * are met:
  33  * 1. Redistributions of source code must retain the above copyright
  34  *    notice, this list of conditions and the following disclaimer.
  35  * 2. Redistributions in binary form must reproduce the above copyright
  36  *    notice, this list of conditions and the following disclaimer in the
  37  *    documentation and/or other materials provided with the distribution.
  38  * 3. All advertising materials mentioning features or use of this software
  39  *    must display the following acknowledgement:
  40  *      This product includes software developed by the University of
  41  *      California, Berkeley and its contributors.
  42  * 4. Neither the name of the University nor the names of its contributors
  43  *    may be used to endorse or promote products derived from this software
  44  *    without specific prior written permission.
  45  *
  46  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  47  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  48  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  49  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  50  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  51  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  52  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  53  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  54  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  55  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  56  * SUCH DAMAGE.
  57  */
  58
  59 #if defined(LIBC_SCCS) && !defined(lint)
  60 static char sccsid[] = "@(#)bt_search.c 8.8 (Berkeley) 7/31/94";
  61 #endif /* LIBC_SCCS and not lint */
  62 #include <sys/cdefs.h>
  63
  64 #include <sys/types.h>
  65
  66 #include <stdio.h>
  67
  68 #include <db.h>
  69 #include "btree.h"
  70
  71 static int __bt_snext(BTREE *, PAGE *, const DBT *, int *);
  72 static int __bt_sprev(BTREE *, PAGE *, const DBT *, int *);
  73
  74 /*
  75  * __bt_search --
  76  *      Search a btree for a key.
  77  *
  78  * Parameters:
  79  *      t:      tree to search
  80  *      key:    key to find
  81  *      exactp: pointer to exact match flag
  82  *
  83  * Returns:
  84  *      The EPG for matching record, if any, or the EPG for the location
  85  *      of the key, if it were inserted into the tree, is entered into
  86  *      the bt_cur field of the tree.  A pointer to the field is returned.
  87  */
  88 EPG *
  89 __bt_search(t, key, exactp)
  90         BTREE *t;
  91         const DBT *key;
  92         int *exactp;
  93 {
  94         PAGE *h;
  95         indx_t base, index, lim;
  96         pgno_t pg;
  97         int cmp;
  98
  99         BT_CLR(t);
 100         for (pg = P_ROOT;;) {
 101                 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
 102                         return (NULL);
 103
 104                 /* Do a binary search on the current page. */
 105                 t->bt_cur.page = h;
 106                 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) {
 107                         t->bt_cur.index = index = base + (lim >> 1);
 108                         if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) {
 109                                 if (h->flags & P_BLEAF) {
 110                                         *exactp = 1;
 111                                         return (&t->bt_cur);
 112                                 }
 113                                 goto next;
 114                         }
 115                         if (cmp > 0) {
 116                                 base = index + 1;
 117                                 --lim;
 118                         }
 119                 }
 120
 121                 /*
 122                  * If it's a leaf page, we're almost done.  If no duplicates
 123                  * are allowed, or we have an exact match, we're done.  Else,
 124                  * it's possible that there were matching keys on this page,
 125                  * which later deleted, and we're on a page with no matches
 126                  * while there are matches on other pages.  If at the start or
 127                  * end of a page, check the adjacent page.
 128                  */
 129                 if (h->flags & P_BLEAF) {
 130                         if (!F_ISSET(t, B_NODUPS)) {
 131                                 if (base == 0 &&
 132                                     h->prevpg != P_INVALID &&
 133                                     __bt_sprev(t, h, key, exactp))
 134                                         return (&t->bt_cur);
 135                                 if (base == NEXTINDEX(h) &&
 136                                     h->nextpg != P_INVALID &&
 137                                     __bt_snext(t, h, key, exactp))
 138                                         return (&t->bt_cur);
 139                         }
 140                         *exactp = 0;
 141                         t->bt_cur.index = base;
 142                         return (&t->bt_cur);
 143                 }
 144
 145                 /*
 146                  * No match found.  Base is the smallest index greater than
 147                  * key and may be zero or a last + 1 index.  If it's non-zero,
 148                  * decrement by one, and record the internal page which should
 149                  * be a parent page for the key.  If a split later occurs, the
 150                  * inserted page will be to the right of the saved page.
 151                  */
 152                 index = base ? base - 1 : base;
 153
 154 next:           BT_PUSH(t, h->pgno, index);
 155                 pg = GETBINTERNAL(h, index)->pgno;
 156                 mpool_put(t->bt_mp, h, 0);
 157         }
 158 }
 159
 160 /*
 161  * __bt_snext --
 162  *      Check for an exact match after the key.
 163  *
 164  * Parameters:
 165  *      t:      tree
 166  *      h:      current page
 167  *      key:    key
 168  *      exactp: pointer to exact match flag
 169  *
 170  * Returns:
 171  *      If an exact match found.
 172  */
 173 static int
 174 __bt_snext(t, h, key, exactp)
 175         BTREE *t;
 176         PAGE *h;
 177         const DBT *key;
 178         int *exactp;
 179 {
 180         EPG e;
 181
 182         /*
 183          * Get the next page.  The key is either an exact
 184          * match, or not as good as the one we already have.
 185          */
 186         if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
 187                 return (0);
 188         e.index = 0;
 189         if (__bt_cmp(t, key, &e) == 0) {
 190                 mpool_put(t->bt_mp, h, 0);
 191                 t->bt_cur = e;
 192                 *exactp = 1;
 193                 return (1);
 194         }
 195         mpool_put(t->bt_mp, e.page, 0);
 196         return (0);
 197 }
 198
 199 /*
 200  * __bt_sprev --
 201  *      Check for an exact match before the key.
 202  *
 203  * Parameters:
 204  *      t:      tree
 205  *      h:      current page
 206  *      key:    key
 207  *      exactp: pointer to exact match flag
 208  *
 209  * Returns:
 210  *      If an exact match found.
 211  */
 212 static int
 213 __bt_sprev(t, h, key, exactp)
 214         BTREE *t;
 215         PAGE *h;
 216         const DBT *key;
 217         int *exactp;
 218 {
 219         EPG e;
 220
 221         /*
 222          * Get the previous page.  The key is either an exact
 223          * match, or not as good as the one we already have.
 224          */
 225         if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
 226                 return (0);
 227         e.index = NEXTINDEX(e.page) - 1;
 228         if (__bt_cmp(t, key, &e) == 0) {
 229                 mpool_put(t->bt_mp, h, 0);
 230                 t->bt_cur = e;
 231                 *exactp = 1;
 232                 return (1);
 233         }
 234         mpool_put(t->bt_mp, e.page, 0);
 235         return (0);
 236 }