bt_seq.c

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/*-
 * 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_seq.c   8.7 (Berkeley) 7/20/94";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>

#include "../include/db.h"
#include "btree.h"

static int __bt_first __P((BTREE *, const DBT *, EPG *, int *));
static int __bt_seqadv __P((BTREE *, EPG *, int));
static int __bt_seqset __P((BTREE *, EPG *, DBT *, int));

/*
 * Sequential scan support.
 *
 * The tree can be scanned sequentially, starting from either end of the
 * tree or from any specific key.  A scan request before any scanning is
 * done is initialized as starting from the least node.
 */

/*
 * __bt_seq --
 * Btree sequential scan interface.
 *
 * Parameters:
 * dbp:  pointer to access method
 * key:  key for positioning and return value
 * data: data return value
 * flags:   R_CURSOR, R_FIRST, R_LAST, R_NEXT, R_PREV.
 *
 * Returns:
 * RET_ERROR, RET_SUCCESS or RET_SPECIAL if there's no next key.
 */
int
__bt_seq(dbp, key, data, flags)
   const DB *dbp;
   DBT *key, *data;
   u_int flags;
{
   BTREE *t;
   EPG e;
   int status;

   t = dbp->internal;

   /* Toss any page pinned across calls. */
   if (t->bt_pinned != NULL) {
      mpool_put(t->bt_mp, t->bt_pinned, 0);
      t->bt_pinned = NULL;
   }

   /*
    * If scan uninitialized as yet, or starting at a specific record, set
    * the scan to a specific key.  Both __bt_seqset and __bt_seqadv pin
    * the page the cursor references if they're successful.
    */
   switch (flags) {
   case R_NEXT:
   case R_PREV:
      if (F_ISSET(&t->bt_cursor, CURS_INIT)) {
         status = __bt_seqadv(t, &e, flags);
         break;
      }
      /* FALLTHROUGH */
   case R_FIRST:
   case R_LAST:
   case R_CURSOR:
      status = __bt_seqset(t, &e, key, flags);
      break;
   default:
      errno = EINVAL;
      return (RET_ERROR);
   }

   if (status == RET_SUCCESS) {
      __bt_setcur(t, e.page->pgno, e.index);

      status =
          __bt_ret(t, &e, key, &t->bt_rkey, data, &t->bt_rdata, 0);

      /*
       * If the user is doing concurrent access, we copied the
       * key/data, toss the page.
       */
      if (F_ISSET(t, B_DB_LOCK))
         mpool_put(t->bt_mp, e.page, 0);
      else
         t->bt_pinned = e.page;
   }
   return (status);
}

/*
 * __bt_seqset --
 * Set the sequential scan to a specific key.
 *
 * Parameters:
 * t: tree
 * ep:   storage for returned key
 * key:  key for initial scan position
 * flags:   R_CURSOR, R_FIRST, R_LAST, R_NEXT, R_PREV
 *
 * Side effects:
 * Pins the page the cursor references.
 *
 * Returns:
 * RET_ERROR, RET_SUCCESS or RET_SPECIAL if there's no next key.
 */
static int
__bt_seqset(t, ep, key, flags)
   BTREE *t;
   EPG *ep;
   DBT *key;
   int flags;
{
   PAGE *h;
   pgno_t pg;
   int exact;

   /*
    * Find the first, last or specific key in the tree and point the
    * cursor at it.  The cursor may not be moved until a new key has
    * been found.
    */
   switch (flags) {
   case R_CURSOR:          /* Keyed scan. */
      /*
       * Find the first instance of the key or the smallest key
       * which is greater than or equal to the specified key.
       */
      if (key->data == NULL || key->size == 0) {
         errno = EINVAL;
         return (RET_ERROR);
      }
      return (__bt_first(t, key, ep, &exact));
   case R_FIRST:           /* First record. */
   case R_NEXT:
      /* Walk down the left-hand side of the tree. */
      for (pg = P_ROOT;;) {
         if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
            return (RET_ERROR);

         /* Check for an empty tree. */
         if (NEXTINDEX(h) == 0) {
            mpool_put(t->bt_mp, h, 0);
            return (RET_SPECIAL);
         }

         if (h->flags & (P_BLEAF | P_RLEAF))
            break;
         pg = GETBINTERNAL(h, 0)->pgno;
         mpool_put(t->bt_mp, h, 0);
      }
      ep->page = h;
      ep->index = 0;
      break;
   case R_LAST:            /* Last record. */
   case R_PREV:
      /* Walk down the right-hand side of the tree. */
      for (pg = P_ROOT;;) {
         if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
            return (RET_ERROR);

         /* Check for an empty tree. */
         if (NEXTINDEX(h) == 0) {
            mpool_put(t->bt_mp, h, 0);
            return (RET_SPECIAL);
         }

         if (h->flags & (P_BLEAF | P_RLEAF))
            break;
         pg = GETBINTERNAL(h, NEXTINDEX(h) - 1)->pgno;
         mpool_put(t->bt_mp, h, 0);
      }

      ep->page = h;
      ep->index = NEXTINDEX(h) - 1;
      break;
   }
   return (RET_SUCCESS);
}

/*
 * __bt_seqadvance --
 * Advance the sequential scan.
 *
 * Parameters:
 * t: tree
 * flags:   R_NEXT, R_PREV
 *
 * Side effects:
 * Pins the page the new key/data record is on.
 *
 * Returns:
 * RET_ERROR, RET_SUCCESS or RET_SPECIAL if there's no next key.
 */
static int
__bt_seqadv(t, ep, flags)
   BTREE *t;
   EPG *ep;
   int flags;
{
   CURSOR *c;
   PAGE *h;
   indx_t index = 0;
   pgno_t pg;
   int exact;

   /*
    * There are a couple of states that we can be in.  The cursor has
    * been initialized by the time we get here, but that's all we know.
    */
   c = &t->bt_cursor;

   /*
    * The cursor was deleted where there weren't any duplicate records,
    * so the key was saved.  Find out where that key would go in the
    * current tree.  It doesn't matter if the returned key is an exact
    * match or not -- if it's an exact match, the record was added after
    * the delete so we can just return it.  If not, as long as there's
    * a record there, return it.
    */
   if (F_ISSET(c, CURS_ACQUIRE))
      return (__bt_first(t, &c->key, ep, &exact));

   /* Get the page referenced by the cursor. */
   if ((h = mpool_get(t->bt_mp, c->pg.pgno, 0)) == NULL)
      return (RET_ERROR);

   /*
    * Find the next/previous record in the tree and point the cursor at
    * it.  The cursor may not be moved until a new key has been found.
    */
   switch (flags) {
   case R_NEXT:         /* Next record. */
      /*
       * The cursor was deleted in duplicate records, and moved
       * forward to a record that has yet to be returned.  Clear
       * that flag, and return the record.
       */
      if (F_ISSET(c, CURS_AFTER))
         goto usecurrent;
      index = c->pg.index;
      if (++index == NEXTINDEX(h)) {
         pg = h->nextpg;
         mpool_put(t->bt_mp, h, 0);
         if (pg == P_INVALID)
            return (RET_SPECIAL);
         if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
            return (RET_ERROR);
         index = 0;
      }
      break;
   case R_PREV:         /* Previous record. */
      /*
       * The cursor was deleted in duplicate records, and moved
       * backward to a record that has yet to be returned.  Clear
       * that flag, and return the record.
       */
      if (F_ISSET(c, CURS_BEFORE)) {
usecurrent:    F_CLR(c, CURS_AFTER | CURS_BEFORE);
         ep->page = h;
         ep->index = c->pg.index;
         return (RET_SUCCESS);
      }
      index = c->pg.index;
      if (index == 0) {
         pg = h->prevpg;
         mpool_put(t->bt_mp, h, 0);
         if (pg == P_INVALID)
            return (RET_SPECIAL);
         if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
            return (RET_ERROR);
         index = NEXTINDEX(h) - 1;
      } else
         --index;
      break;
   }

   ep->page = h;
   ep->index = index;
   return (RET_SUCCESS);
}

/*
 * __bt_first --
 * Find the first entry.
 *
 * Parameters:
 * t: the tree
 *    key:  the key
 *  erval:  return EPG
 * exactp:  pointer to exact match flag
 *
 * Returns:
 * The first entry in the tree greater than or equal to key,
 * or RET_SPECIAL if no such key exists.
 */
static int
__bt_first(t, key, erval, exactp)
   BTREE *t;
   const DBT *key;
   EPG *erval;
   int *exactp;
{
   PAGE *h;
   EPG *ep, save;
   pgno_t pg;

   /*
    * Find any matching record; __bt_search pins the page.
    *
    * If it's an exact match and duplicates are possible, walk backwards
    * in the tree until we find the first one.  Otherwise, make sure it's
    * a valid key (__bt_search may return an index just past the end of a
    * page) and return it.
    */
   if ((ep = __bt_search(t, key, exactp)) == NULL)
      return (RET_SPECIAL);
   if (*exactp) {
      if (F_ISSET(t, B_NODUPS)) {
         *erval = *ep;
         return (RET_SUCCESS);
      }

      /*
       * Walk backwards, as long as the entry matches and there are
       * keys left in the tree.  Save a copy of each match in case
       * we go too far.
       */
      save = *ep;
      h = ep->page;
      do {
         if (save.page->pgno != ep->page->pgno) {
            mpool_put(t->bt_mp, save.page, 0);
            save = *ep;
         } else
            save.index = ep->index;

         /*
          * Don't unpin the page the last (or original) match
          * was on, but make sure it's unpinned if an error
          * occurs.
          */
         if (ep->index == 0) {
            if (h->prevpg == P_INVALID)
               break;
            if (h->pgno != save.page->pgno)
               mpool_put(t->bt_mp, h, 0);
            if ((h = mpool_get(t->bt_mp,
                h->prevpg, 0)) == NULL) {
               if (h->pgno == save.page->pgno)
                  mpool_put(t->bt_mp,
                      save.page, 0);
               return (RET_ERROR);
            }
            ep->page = h;
            ep->index = NEXTINDEX(h);
         }
         --ep->index;
      } while (__bt_cmp(t, key, ep) == 0);

      /*
       * Reach here with the last page that was looked at pinned,
       * which may or may not be the same as the last (or original)
       * match page.  If it's not useful, release it.
       */
      if (h->pgno != save.page->pgno)
         mpool_put(t->bt_mp, h, 0);

      *erval = save;
      return (RET_SUCCESS);
   }

   /* If at the end of a page, find the next entry. */
   if (ep->index == NEXTINDEX(ep->page)) {
      h = ep->page;
      pg = h->nextpg;
      mpool_put(t->bt_mp, h, 0);
      if (pg == P_INVALID)
         return (RET_SPECIAL);
      if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
         return (RET_ERROR);
      ep->index = 0;
      ep->page = h;
   }
   *erval = *ep;
   return (RET_SUCCESS);
}

/*
 * __bt_setcur --
 * Set the cursor to an entry in the tree.
 *
 * Parameters:
 * t: the tree
 *   pgno:  page number
 *  index:  page index
 */
void
__bt_setcur(t, pgno, index)
   BTREE *t;
   pgno_t pgno;
   u_int index;
{
   /* Lose any already deleted key. */
   if (t->bt_cursor.key.data != NULL) {
      free(t->bt_cursor.key.data);
      t->bt_cursor.key.size = 0;
      t->bt_cursor.key.data = NULL;
   }
   F_CLR(&t->bt_cursor, CURS_ACQUIRE | CURS_AFTER | CURS_BEFORE);

   /* Update the cursor. */
   t->bt_cursor.pg.pgno = pgno;
   t->bt_cursor.pg.index = index;
   F_SET(&t->bt_cursor, CURS_INIT);
}