db/btree/bt_get.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23  * Copyright (c) 1990, 1993
  24  *      The Regents of the University of California.  All rights reserved.
  25  *
  26  * This code is derived from software contributed to Berkeley by
  27  * Mike Olson.
  28  *
  29  * Redistribution and use in source and binary forms, with or without
  30  * modification, are permitted provided that the following conditions
  31  * are met:
  32  * 1. Redistributions of source code must retain the above copyright
  33  *    notice, this list of conditions and the following disclaimer.
  34  * 2. Redistributions in binary form must reproduce the above copyright
  35  *    notice, this list of conditions and the following disclaimer in the
  36  *    documentation and/or other materials provided with the distribution.
  37  * 3. All advertising materials mentioning features or use of this software
  38  *    must display the following acknowledgement:
  39  *      This product includes software developed by the University of
  40  *      California, Berkeley and its contributors.
  41  * 4. Neither the name of the University nor the names of its contributors
  42  *    may be used to endorse or promote products derived from this software
  43  *    without specific prior written permission.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  */
  57
  58
  59 #include <sys/types.h>
  60
  61 #include <errno.h>
  62 #include <stddef.h>
  63 #include <stdio.h>
  64
  65 #include <db.h>
  66 #include "btree.h"
  67
  68 /*
  69  * __BT_GET -- Get a record from the btree.
  70  *
  71  * Parameters:
  72  *      dbp:    pointer to access method
  73  *      key:    key to find
  74  *      data:   data to return
  75  *      flag:   currently unused
  76  *
  77  * Returns:
  78  *      RET_ERROR, RET_SUCCESS and RET_SPECIAL if the key not found.
  79  */
  80 int
  81 __bt_get(dbp, key, data, flags)
  82         const DB *dbp;
  83         const DBT *key;
  84         DBT *data;
  85         u_int flags;
  86 {
  87         BTREE *t;
  88         EPG *e;
  89         int exact, status;
  90
  91         t = dbp->internal;
  92
  93         /* Toss any page pinned across calls. */
  94         if (t->bt_pinned != NULL) {
  95                 mpool_put(t->bt_mp, t->bt_pinned, 0);
  96                 t->bt_pinned = NULL;
  97         }
  98
  99         /* Get currently doesn't take any flags. */
 100         if (flags) {
 101                 errno = EINVAL;
 102                 return (RET_ERROR);
 103         }
 104
 105         if ((e = __bt_search(t, key, &exact)) == NULL)
 106                 return (RET_ERROR);
 107         if (!exact) {
 108                 mpool_put(t->bt_mp, e->page, 0);
 109                 return (RET_SPECIAL);
 110         }
 111
 112         /*
 113          * A special case is if we found the record but it's flagged for
 114          * deletion.  In this case, we want to find another record with the
 115          * same key, if it exists.  Rather than look around the tree we call
 116          * __bt_first and have it redo the search, as __bt_first will not
 117          * return keys marked for deletion.  Slow, but should never happen.
 118          */
 119         if (ISSET(t, B_DELCRSR) && e->page->pgno == t->bt_bcursor.pgno &&
 120             e->index == t->bt_bcursor.index) {
 121                 mpool_put(t->bt_mp, e->page, 0);
 122                 if ((e = __bt_first(t, key, &exact)) == NULL)
 123                         return (RET_ERROR);
 124                 if (!exact)
 125                         return (RET_SPECIAL);
 126         }
 127
 128         status = __bt_ret(t, e, NULL, data);
 129         /*
 130          * If the user is doing concurrent access, we copied the
 131          * key/data, toss the page.
 132          */
 133         if (ISSET(t, B_DB_LOCK))
 134                 mpool_put(t->bt_mp, e->page, 0);
 135         else
 136                 t->bt_pinned = e->page;
 137         return (status);
 138 }
 139
 140 /*
 141  * __BT_FIRST -- Find the first entry.
 142  *
 143  * Parameters:
 144  *      t:      the tree
 145  *      key:    the key
 146  *
 147  * Returns:
 148  *      The first entry in the tree greater than or equal to key.
 149  */
 150 EPG *
 151 __bt_first(t, key, exactp)
 152         BTREE *t;
 153         const DBT *key;
 154         int *exactp;
 155 {
 156         register PAGE *h;
 157         register EPG *e;
 158         EPG save;
 159         pgno_t cpgno, pg;
 160         indx_t cindex;
 161         int found;
 162
 163         /*
 164          * Find any matching record; __bt_search pins the page.  Only exact
 165          * matches are tricky, otherwise just return the location of the key
 166          * if it were to be inserted into the tree.
 167          */
 168         if ((e = __bt_search(t, key, exactp)) == NULL)
 169                 return (NULL);
 170         if (!*exactp)
 171                 return (e);
 172
 173         if (ISSET(t, B_DELCRSR)) {
 174                 cpgno = t->bt_bcursor.pgno;
 175                 cindex = t->bt_bcursor.index;
 176         } else {
 177                 cpgno = P_INVALID;
 178                 cindex = 0;             /* GCC thinks it's uninitialized. */
 179         }
 180
 181         /*
 182          * Walk backwards, skipping empty pages, as long as the entry matches
 183          * and there are keys left in the tree.  Save a copy of each match in
 184          * case we go too far.  A special case is that we don't return a match
 185          * on records that the cursor references that have already been flagged
 186          * for deletion.
 187          */
 188         save = *e;
 189         h = e->page;
 190         found = 0;
 191         do {
 192                 if (cpgno != h->pgno || cindex != e->index) {
 193                         if (save.page->pgno != e->page->pgno) {
 194                                 mpool_put(t->bt_mp, save.page, 0);
 195                                 save = *e;
 196                         } else
 197                                 save.index = e->index;
 198                         found = 1;
 199                 }
 200                 /*
 201                  * Make a special effort not to unpin the page the last (or
 202                  * original) match was on, but also make sure it's unpinned
 203                  * if an error occurs.
 204                  */
 205                 while (e->index == 0) {
 206                         if (h->prevpg == P_INVALID)
 207                                 goto done1;
 208                         if (h->pgno != save.page->pgno)
 209                                 mpool_put(t->bt_mp, h, 0);
 210                         if ((h = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) {
 211                                 if (h->pgno == save.page->pgno)
 212                                         mpool_put(t->bt_mp, save.page, 0);
 213                                 return (NULL);
 214                         }
 215                         e->page = h;
 216                         e->index = NEXTINDEX(h);
 217                 }
 218                 --e->index;
 219         } while (__bt_cmp(t, key, e) == 0);
 220
 221         /*
 222          * Reach here with the last page that was looked at pinned, which may
 223          * or may not be the same as the last (or original) match page.  If
 224          * it's not useful, release it.
 225          */
 226 done1:  if (h->pgno != save.page->pgno)
 227                 mpool_put(t->bt_mp, h, 0);
 228
 229         /*
 230          * If still haven't found a record, the only possibility left is the
 231          * next one.  Move forward one slot, skipping empty pages and check.
 232          */
 233         if (!found) {
 234                 h = save.page;
 235                 if (++save.index == NEXTINDEX(h)) {
 236                         do {
 237                                 pg = h->nextpg;
 238                                 mpool_put(t->bt_mp, h, 0);
 239                                 if (pg == P_INVALID) {
 240                                         *exactp = 0;
 241                                         return (e);
 242                                 }
 243                                 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
 244                                         return (NULL);
 245                         } while ((save.index = NEXTINDEX(h)) == 0);
 246                         save.page = h;
 247                 }
 248                 if (__bt_cmp(t, key, &save) != 0) {
 249                         *exactp = 0;
 250                         return (e);
 251                 }
 252         }
 253         *e = save;
 254         *exactp = 1;
 255         return (e);
 256 }