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bt_seq.c

/*-
 * 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 <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 unitialized 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;
      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);
}

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