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bt_delete.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *    Sleepycat Software.  All rights reserved.
 */
/*
 * Copyright (c) 1990, 1993, 1994, 1995, 1996
 *    Keith Bostic.  All rights reserved.
 */
/*
 * Copyright (c) 1990, 1993, 1994, 1995
 *    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.
 */

#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)bt_delete.c   10.43 (Sleepycat) 12/7/98";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <string.h>
#endif

#include "db_int.h"
#include "db_page.h"
#include "btree.h"

/*
 * __bam_delete --
 *    Delete the items referenced by a key.
 *
 * PUBLIC: int __bam_delete __P((DB *, DB_TXN *, DBT *, u_int32_t));
 */
int
__bam_delete(dbp, txn, key, flags)
      DB *dbp;
      DB_TXN *txn;
      DBT *key;
      u_int32_t flags;
{
      DBC *dbc;
      DBT data;
      u_int32_t f_init, f_next;
      int ret, t_ret;

      DB_PANIC_CHECK(dbp);

      /* Check for invalid flags. */
      if ((ret =
          __db_delchk(dbp, key, flags, F_ISSET(dbp, DB_AM_RDONLY))) != 0)
            return (ret);

      /* Allocate a cursor. */
      if ((ret = dbp->cursor(dbp, txn, &dbc, DB_WRITELOCK)) != 0)
            return (ret);

      DEBUG_LWRITE(dbc, txn, "bam_delete", key, NULL, flags);

      /*
       * Walk a cursor through the key/data pairs, deleting as we go.  Set
       * the DB_DBT_USERMEM flag, as this might be a threaded application
       * and the flags checking will catch us.  We don't actually want the
       * keys or data, so request a partial of length 0.
       */
      memset(&data, 0, sizeof(data));
      F_SET(&data, DB_DBT_USERMEM | DB_DBT_PARTIAL);

      /* If locking, set read-modify-write flag. */
      f_init = DB_SET;
      f_next = DB_NEXT_DUP;
      if (dbp->dbenv != NULL && dbp->dbenv->lk_info != NULL) {
            f_init |= DB_RMW;
            f_next |= DB_RMW;
      }

      /* Walk through the set of key/data pairs, deleting as we go. */
      if ((ret = dbc->c_get(dbc, key, &data, f_init)) != 0)
            goto err;
      for (;;) {
            if ((ret = dbc->c_del(dbc, 0)) != 0)
                  goto err;
            if ((ret = dbc->c_get(dbc, key, &data, f_next)) != 0) {
                  if (ret == DB_NOTFOUND) {
                        ret = 0;
                        break;
                  }
                  goto err;
            }
      }

err:  /* Discard the cursor. */
      if ((t_ret = dbc->c_close(dbc)) != 0 &&
          (ret == 0 || ret == DB_NOTFOUND))
            ret = t_ret;

      return (ret);
}

/*
 * __bam_ditem --
 *    Delete one or more entries from a page.
 *
 * PUBLIC: int __bam_ditem __P((DBC *, PAGE *, u_int32_t));
 */
int
__bam_ditem(dbc, h, indx)
      DBC *dbc;
      PAGE *h;
      u_int32_t indx;
{
      BINTERNAL *bi;
      BKEYDATA *bk;
      BOVERFLOW *bo;
      DB *dbp;
      u_int32_t nbytes;
      int ret;

      dbp = dbc->dbp;

      switch (TYPE(h)) {
      case P_IBTREE:
            bi = GET_BINTERNAL(h, indx);
            switch (B_TYPE(bi->type)) {
            case B_DUPLICATE:
            case B_OVERFLOW:
                  nbytes = BINTERNAL_SIZE(bi->len);
                  bo = (BOVERFLOW *)bi->data;
                  goto offpage;
            case B_KEYDATA:
                  nbytes = BINTERNAL_SIZE(bi->len);
                  break;
            default:
                  return (__db_pgfmt(dbp, h->pgno));
            }
            break;
      case P_IRECNO:
            nbytes = RINTERNAL_SIZE;
            break;
      case P_LBTREE:
            /*
             * If it's a duplicate key, discard the index and don't touch
             * the actual page item.
             *
             * XXX
             * This works because no data item can have an index matching
             * any other index so even if the data item is in a key "slot",
             * it won't match any other index.
             */
            if ((indx % 2) == 0) {
                  /*
                   * Check for a duplicate after us on the page.  NOTE:
                   * we have to delete the key item before deleting the
                   * data item, otherwise the "indx + P_INDX" calculation
                   * won't work!
                   */
                  if (indx + P_INDX < (u_int32_t)NUM_ENT(h) &&
                      h->inp[indx] == h->inp[indx + P_INDX])
                        return (__bam_adjindx(dbc,
                            h, indx, indx + O_INDX, 0));
                  /*
                   * Check for a duplicate before us on the page.  It
                   * doesn't matter if we delete the key item before or
                   * after the data item for the purposes of this one.
                   */
                  if (indx > 0 && h->inp[indx] == h->inp[indx - P_INDX])
                        return (__bam_adjindx(dbc,
                            h, indx, indx - P_INDX, 0));
            }
            /* FALLTHROUGH */
      case P_LRECNO:
            bk = GET_BKEYDATA(h, indx);
            switch (B_TYPE(bk->type)) {
            case B_DUPLICATE:
            case B_OVERFLOW:
                  nbytes = BOVERFLOW_SIZE;
                  bo = GET_BOVERFLOW(h, indx);

offpage:          /* Delete duplicate/offpage chains. */
                  if (B_TYPE(bo->type) == B_DUPLICATE) {
                        if ((ret =
                            __db_ddup(dbc, bo->pgno, __bam_free)) != 0)
                              return (ret);
                  } else
                        if ((ret =
                            __db_doff(dbc, bo->pgno, __bam_free)) != 0)
                              return (ret);
                  break;
            case B_KEYDATA:
                  nbytes = BKEYDATA_SIZE(bk->len);
                  break;
            default:
                  return (__db_pgfmt(dbp, h->pgno));
            }
            break;
      default:
            return (__db_pgfmt(dbp, h->pgno));
      }

      /* Delete the item. */
      if ((ret = __db_ditem(dbc, h, indx, nbytes)) != 0)
            return (ret);

      /* Mark the page dirty. */
      return (memp_fset(dbp->mpf, h, DB_MPOOL_DIRTY));
}

/*
 * __bam_adjindx --
 *    Adjust an index on the page.
 *
 * PUBLIC: int __bam_adjindx __P((DBC *, PAGE *, u_int32_t, u_int32_t, int));
 */
int
__bam_adjindx(dbc, h, indx, indx_copy, is_insert)
      DBC *dbc;
      PAGE *h;
      u_int32_t indx, indx_copy;
      int is_insert;
{
      DB *dbp;
      db_indx_t copy;
      int ret;

      dbp = dbc->dbp;

      /* Log the change. */
      if (DB_LOGGING(dbc) &&
          (ret = __bam_adj_log(dbp->dbenv->lg_info, dbc->txn, &LSN(h),
          0, dbp->log_fileid, PGNO(h), &LSN(h), indx, indx_copy,
          (u_int32_t)is_insert)) != 0)
            return (ret);

      if (is_insert) {
            copy = h->inp[indx_copy];
            if (indx != NUM_ENT(h))
                  memmove(&h->inp[indx + O_INDX], &h->inp[indx],
                      sizeof(db_indx_t) * (NUM_ENT(h) - indx));
            h->inp[indx] = copy;
            ++NUM_ENT(h);
      } else {
            --NUM_ENT(h);
            if (indx != NUM_ENT(h))
                  memmove(&h->inp[indx], &h->inp[indx + O_INDX],
                      sizeof(db_indx_t) * (NUM_ENT(h) - indx));
      }

      /* Mark the page dirty. */
      ret = memp_fset(dbp->mpf, h, DB_MPOOL_DIRTY);

      /* Adjust the cursors. */
      __bam_ca_di(dbp, h->pgno, indx, is_insert ? 1 : -1);
      return (0);
}

/*
 * __bam_dpage --
 *    Delete a page from the tree.
 *
 * PUBLIC: int __bam_dpage __P((DBC *, const DBT *));
 */
int
__bam_dpage(dbc, key)
      DBC *dbc;
      const DBT *key;
{
      CURSOR *cp;
      DB *dbp;
      DB_LOCK lock;
      PAGE *h;
      db_pgno_t pgno;
      int level;        /* !!!: has to hold number of tree levels. */
      int exact, ret;

      dbp = dbc->dbp;
      cp = dbc->internal;
      ret = 0;

      /*
       * The locking protocol is that we acquire locks by walking down the
       * tree, to avoid the obvious deadlocks.
       *
       * Call __bam_search to reacquire the empty leaf page, but this time
       * get both the leaf page and it's parent, locked.  Walk back up the
       * tree, until we have the top pair of pages that we want to delete.
       * Once we have the top page that we want to delete locked, lock the
       * underlying pages and check to make sure they're still empty.  If
       * they are, delete them.
       */
      for (level = LEAFLEVEL;; ++level) {
            /* Acquire a page and its parent, locked. */
            if ((ret =
                __bam_search(dbc, key, S_WRPAIR, level, NULL, &exact)) != 0)
                  return (ret);

            /*
             * If we reach the root or the page isn't going to be empty
             * when we delete one record, quit.
             */
            h = cp->csp[-1].page;
            if (h->pgno == PGNO_ROOT || NUM_ENT(h) != 1)
                  break;

            /* Release the two locked pages. */
            (void)memp_fput(dbp->mpf, cp->csp[-1].page, 0);
            (void)__BT_TLPUT(dbc, cp->csp[-1].lock);
            (void)memp_fput(dbp->mpf, cp->csp[0].page, 0);
            (void)__BT_TLPUT(dbc, cp->csp[0].lock);
      }

      /*
       * Leave the stack pointer one after the last entry, we may be about
       * to push more items on the stack.
       */
      ++cp->csp;

      /*
       * cp->csp[-2].page is the top page, which we're not going to delete,
       * and cp->csp[-1].page is the first page we are going to delete.
       *
       * Walk down the chain, acquiring the rest of the pages until we've
       * retrieved the leaf page.  If we find any pages that aren't going
       * to be emptied by the delete, someone else added something while we
       * were walking the tree, and we discontinue the delete.
       */
      for (h = cp->csp[-1].page;;) {
            if (ISLEAF(h)) {
                  if (NUM_ENT(h) != 0)
                        goto release;
                  break;
            } else
                  if (NUM_ENT(h) != 1)
                        goto release;

            /*
             * Get the next page, write lock it and push it onto the stack.
             * We know it's index 0, because it can only have one element.
             */
            pgno = TYPE(h) == P_IBTREE ?
                GET_BINTERNAL(h, 0)->pgno : GET_RINTERNAL(h, 0)->pgno;

            if ((ret = __bam_lget(dbc, 0, pgno, DB_LOCK_WRITE, &lock)) != 0)
                  goto release;
            if ((ret = memp_fget(dbp->mpf, &pgno, 0, &h)) != 0)
                  goto release;
            BT_STK_PUSH(cp, h, 0, lock, ret);
      }

      /* Adjust back to reference the last page on the stack. */
      BT_STK_POP(cp);

      /* Delete the pages. */
      return (__bam_dpages(dbc));

release:
      /* Adjust back to reference the last page on the stack. */
      BT_STK_POP(cp);

      /* Discard any locked pages and return. */
      __bam_stkrel(dbc, 0);

      return (ret);
}

/*
 * __bam_dpages --
 *    Delete a set of locked pages.
 *
 * PUBLIC: int __bam_dpages __P((DBC *));
 */
int
__bam_dpages(dbc)
      DBC *dbc;
{
      CURSOR *cp;
      DB *dbp;
      DBT a, b;
      DB_LOCK c_lock, p_lock;
      EPG *epg;
      PAGE *child, *parent;
      db_indx_t nitems;
      db_pgno_t pgno;
      db_recno_t rcnt;
      int done, ret;

      dbp = dbc->dbp;
      cp = dbc->internal;
      epg = cp->sp;

      /*
       * !!!
       * There is an interesting deadlock situation here.  We have to relink
       * the leaf page chain around the leaf page being deleted.  Consider
       * a cursor walking through the leaf pages, that has the previous page
       * read-locked and is waiting on a lock for the page we're deleting.
       * It will deadlock here.  This is a problem, because if our process is
       * selected to resolve the deadlock, we'll leave an empty leaf page
       * that we can never again access by walking down the tree.  So, before
       * we unlink the subtree, we relink the leaf page chain.
       */
      if ((ret = __db_relink(dbc, DB_REM_PAGE, cp->csp->page, NULL, 1)) != 0)
            goto release;

      /*
       * We have the entire stack of deletable pages locked.
       *
       * Delete the highest page in the tree's reference to the underlying
       * stack of pages.  Then, release that page, letting the rest of the
       * tree get back to business.
       */
      if ((ret = __bam_ditem(dbc, epg->page, epg->indx)) != 0) {
release:    (void)__bam_stkrel(dbc, 0);
            return (ret);
      }

      pgno = epg->page->pgno;
      nitems = NUM_ENT(epg->page);

      (void)memp_fput(dbp->mpf, epg->page, 0);
      (void)__BT_TLPUT(dbc, epg->lock);

      /*
       * Free the rest of the stack of pages.
       *
       * !!!
       * Don't bother checking for errors.  We've unlinked the subtree from
       * the tree, and there's no possibility of recovery outside of doing
       * TXN rollback.
       */
      while (++epg <= cp->csp) {
            /*
             * Delete page entries so they will be restored as part of
             * recovery.
             */
            if (NUM_ENT(epg->page) != 0)
                  (void)__bam_ditem(dbc, epg->page, epg->indx);

            (void)__bam_free(dbc, epg->page);
            (void)__BT_TLPUT(dbc, epg->lock);
      }
      BT_STK_CLR(cp);

      /*
       * Try and collapse the tree a level -- this is only applicable
       * if we've deleted the next-to-last element from the root page.
       *
       * There are two cases when collapsing a tree.
       *
       * If we've just deleted the last item from the root page, there is no
       * further work to be done.  The code above has emptied the root page
       * and freed all pages below it.
       */
      if (pgno != PGNO_ROOT || nitems != 1)
            return (0);

      /*
       * If we just deleted the next-to-last item from the root page, the
       * tree can collapse one or more levels.  While there remains only a
       * single item on the root page, write lock the last page referenced
       * by the root page and copy it over the root page.  If we can't get a
       * write lock, that's okay, the tree just stays deeper than we'd like.
       */
      for (done = 0; !done;) {
            /* Initialize. */
            parent = child = NULL;
            p_lock = c_lock = LOCK_INVALID;

            /* Lock the root. */
            pgno = PGNO_ROOT;
            if ((ret =
                __bam_lget(dbc, 0, pgno, DB_LOCK_WRITE, &p_lock)) != 0)
                  goto stop;
            if ((ret = memp_fget(dbp->mpf, &pgno, 0, &parent)) != 0)
                  goto stop;

            if (NUM_ENT(parent) != 1 ||
                (TYPE(parent) != P_IBTREE && TYPE(parent) != P_IRECNO))
                  goto stop;

            pgno = TYPE(parent) == P_IBTREE ?
                GET_BINTERNAL(parent, 0)->pgno :
                GET_RINTERNAL(parent, 0)->pgno;

            /* Lock the child page. */
            if ((ret =
                __bam_lget(dbc, 0, pgno, DB_LOCK_WRITE, &c_lock)) != 0)
                  goto stop;
            if ((ret = memp_fget(dbp->mpf, &pgno, 0, &child)) != 0)
                  goto stop;

            /* Log the change. */
            if (DB_LOGGING(dbc)) {
                  memset(&a, 0, sizeof(a));
                  a.data = child;
                  a.size = dbp->pgsize;
                  memset(&b, 0, sizeof(b));
                  b.data = P_ENTRY(parent, 0);
                  b.size = BINTERNAL_SIZE(((BINTERNAL *)b.data)->len);
                  __bam_rsplit_log(dbp->dbenv->lg_info, dbc->txn,
                     &child->lsn, 0, dbp->log_fileid, child->pgno, &a,
                     RE_NREC(parent), &b, &parent->lsn);
            }

            /*
             * Make the switch.
             *
             * One fixup -- if the tree has record numbers and we're not
             * converting to a leaf page, we have to preserve the total
             * record count.  Note that we are about to overwrite everything
             * on the parent, including its LSN.  This is actually OK,
             * because the above log message, which describes this update,
             * stores its LSN on the child page.  When the child is copied
             * to the parent, the correct LSN is going to copied into
             * place in the parent.
             */
            COMPQUIET(rcnt, 0);
            if (TYPE(child) == P_IRECNO ||
                (TYPE(child) == P_IBTREE && F_ISSET(dbp, DB_BT_RECNUM)))
                  rcnt = RE_NREC(parent);
            memcpy(parent, child, dbp->pgsize);
            parent->pgno = PGNO_ROOT;
            if (TYPE(child) == P_IRECNO ||
                (TYPE(child) == P_IBTREE && F_ISSET(dbp, DB_BT_RECNUM)))
                  RE_NREC_SET(parent, rcnt);

            /* Mark the pages dirty. */
            memp_fset(dbp->mpf, parent, DB_MPOOL_DIRTY);
            memp_fset(dbp->mpf, child, DB_MPOOL_DIRTY);

            /* Adjust the cursors. */
            __bam_ca_rsplit(dbp, child->pgno, PGNO_ROOT);

            /*
             * Free the page copied onto the root page and discard its
             * lock.  (The call to __bam_free() discards our reference
             * to the page.)
             */
            (void)__bam_free(dbc, child);
            child = NULL;

            if (0) {
stop:             done = 1;
            }
            if (p_lock != LOCK_INVALID)
                  (void)__BT_TLPUT(dbc, p_lock);
            if (parent != NULL)
                  memp_fput(dbp->mpf, parent, 0);
            if (c_lock != LOCK_INVALID)
                  (void)__BT_TLPUT(dbc, c_lock);
            if (child != NULL)
                  memp_fput(dbp->mpf, child, 0);
      }

      return (0);
}

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