bt_search.c

Go to the documentation of this file.

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998, 1999, 2000
 *      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. 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 revid[] = "$Id: bt__search_8c-source.html,v 1.1 2008/06/08 10:13:44 sebdiaz Exp $";
#endif /* not lint */

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

#include <string.h>
#endif

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

/*
 * CDB___bam_search --
 *      Search a btree for a key.
 *
 * PUBLIC: int CDB___bam_search __P((DBC *,
 * PUBLIC:     const DBT *, u_int32_t, int, db_recno_t *, int *));
 */
int
CDB___bam_search(dbc, key, flags, stop, recnop, exactp)
        DBC *dbc;
        const DBT *key;
        u_int32_t flags;
        int stop, *exactp;
        db_recno_t *recnop;
{
        BTREE *t;
        BTREE_CURSOR *cp;
        DB *dbp;
        DB_LOCK lock;
        PAGE *h;
        db_indx_t base, i, indx, lim;
        db_lockmode_t lock_mode;
        db_pgno_t pg;
        db_recno_t recno;
        int adjust, cmp, deloffset, ret, stack;
        int (*func) __P((const DBT *, const DBT *));

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        t = dbp->bt_internal;
        recno = 0;

        BT_STK_CLR(cp);

        /*
         * There are several ways we search a btree tree.  The flags argument
         * specifies if we're acquiring read or write locks, if we position
         * to the first or last item in a set of duplicates, if we return
         * deleted items, and if we are locking pairs of pages.  In addition,
         * if we're modifying record numbers, we have to lock the entire tree
         * regardless.  See btree.h for more details.
         *
         * If write-locking pages, we need to know whether or not to acquire a
         * write lock on a page before getting it.  This depends on how deep it
         * is in tree, which we don't know until we acquire the root page.  So,
         * if we need to lock the root page we may have to upgrade it later,
         * because we won't get the correct lock initially.
         *
         * Retrieve the root page.
         */
try_again:
        pg = cp->root;
        stack = LF_ISSET(S_STACK) && F_ISSET(cp, C_RECNUM);
        lock_mode = stack ? DB_LOCK_WRITE : DB_LOCK_READ;
        if ((ret = CDB___db_lget(dbc, 0, pg, lock_mode, 0, &lock)) != 0)
                return (ret);
        if ((ret = CDB_memp_fget(dbp->mpf, &pg, 0, &h)) != 0) {
                /* Did not read it, so we can release the lock */
                (void)__LPUT(dbc, lock);
                return (ret);
        }

        /*
         * Decide if we need to save this page; if we do, write lock it.
         * We deliberately don't lock-couple on this call.  If the tree
         * is tiny, i.e., one page, and two threads are busily updating
         * the root page, we're almost guaranteed deadlocks galore, as
         * each one gets a read lock and then blocks the other's attempt
         * for a write lock.
         */
        if (!stack &&
            ((LF_ISSET(S_PARENT) && (u_int8_t)(stop + 1) >= h->level) ||
            (LF_ISSET(S_WRITE) && h->level == LEAFLEVEL))) {
                (void)CDB_memp_fput(dbp->mpf, h, 0);
                (void)__LPUT(dbc, lock);
                lock_mode = DB_LOCK_WRITE;
                if ((ret = CDB___db_lget(dbc, 0, pg, lock_mode, 0, &lock)) != 0)
                        return (ret);
                if ((ret = CDB_memp_fget(dbp->mpf, &pg, 0, &h)) != 0) {
                        /* Did not read it, so we can release the lock */
                        (void)__LPUT(dbc, lock);
                        return (ret);
                }
                if (!((LF_ISSET(S_PARENT)
                    && (u_int8_t)(stop + 1) >= h->level) ||
                    (LF_ISSET(S_WRITE) && h->level == LEAFLEVEL))) {
                        /* Someone else split the root, start over. */
                        (void)CDB_memp_fput(dbp->mpf, h, 0);
                        (void)__LPUT(dbc, lock);
                        goto try_again;
                }
                stack = 1;
        }

        /* Choose a comparison function. */
        func = F_ISSET(dbc, DBC_OPD) ?
            (dbp->dup_compare == NULL ? CDB___bam_defcmp : dbp->dup_compare) :
            t->bt_compare;

        for (;;) {
                /*
                 * Do a binary search on the current page.  If we're searching
                 * a Btree leaf page, we have to walk the indices in groups of
                 * two.  If we're searching an internal page or a off-page dup
                 * page, they're an index per page item.  If we find an exact
                 * match on a leaf page, we're done.
                 */
                adjust = TYPE(h) == P_LBTREE ? P_INDX : O_INDX;
                for (base = 0,
                    lim = NUM_ENT(h) / (db_indx_t)adjust; lim != 0; lim >>= 1) {
                        indx = base + ((lim >> 1) * adjust);
                        if ((ret = CDB___bam_cmp(dbp,
                            key, h, indx, func, &cmp)) != 0)
                                goto err;
                        if (cmp == 0) {
                                if (TYPE(h) == P_LBTREE || TYPE(h) == P_LDUP)
                                        goto found;
                                goto next;
                        }
                        if (cmp > 0) {
                                base = indx + adjust;
                                --lim;
                        }
                }

                /*
                 * No match found.  Base is the smallest index greater than
                 * key and may be zero or a last + O_INDX index.
                 *
                 * If it's a leaf page, return base as the "found" value.
                 * Delete only deletes exact matches.
                 */
                if (TYPE(h) == P_LBTREE || TYPE(h) == P_LDUP) {
                        *exactp = 0;

                        if (LF_ISSET(S_EXACT))
                                goto notfound;

                        if (LF_ISSET(S_STK_ONLY)) {
                                BT_STK_NUM(dbp->dbenv, cp, h, base, ret);
                                __LPUT(dbc, lock);
                                (void)CDB_memp_fput(dbp->mpf, h, 0);
                                return (ret);
                        }

                        /*
                         * !!!
                         * Possibly returning a deleted record -- DB_SET_RANGE,
                         * DB_KEYFIRST and DB_KEYLAST don't require an exact
                         * match, and we don't want to walk multiple pages here
                         * to find an undeleted record.  This is handled by the
                         * calling routine.
                         */
                        BT_STK_ENTER(dbp->dbenv,
                            cp, h, base, lock, lock_mode, ret);
                        if (ret != 0)
                                goto err;
                        return (0);
                }

                /*
                 * If it's not a leaf page, record the internal page (which is
                 * a parent page for the key).  Decrement the base by 1 if it's
                 * non-zero so that if a split later occurs, the inserted page
                 * will be to the right of the saved page.
                 */
                indx = base > 0 ? base - O_INDX : base;

                /*
                 * If we're trying to calculate the record number, sum up
                 * all the record numbers on this page up to the indx point.
                 */
next:           if (recnop != NULL)
                        for (i = 0; i < indx; ++i)
                                recno += GET_BINTERNAL(h, i)->nrecs;

                pg = GET_BINTERNAL(h, indx)->pgno;

                if (LF_ISSET(S_STK_ONLY)) {
                        if (stop == h->level) {
                                BT_STK_NUM(dbp->dbenv, cp, h, indx, ret);
                                __LPUT(dbc, lock);
                                (void)CDB_memp_fput(dbp->mpf, h, 0);
                                return (ret);
                        }
                        BT_STK_NUMPUSH(dbp->dbenv, cp, h, indx, ret);
                        (void)CDB_memp_fput(dbp->mpf, h, 0);
                        if ((ret = CDB___db_lget(dbc,
                            LCK_COUPLE, pg, lock_mode, 0, &lock)) != 0) {
                                /*
                                 * Discard our lock and return on failure.  This
                                 * is OK because it only happens when descending
                                 * the tree holding read-locks.
                                 */
                                __LPUT(dbc, lock);
                                return (ret);
                        }
                } else if (stack) {
                        /* Return if this is the lowest page wanted. */
                        if (LF_ISSET(S_PARENT) && stop == h->level) {
                                BT_STK_ENTER(dbp->dbenv,
                                    cp, h, indx, lock, lock_mode, ret);
                                if (ret != 0)
                                        goto err;
                                return (0);
                        }
                        BT_STK_PUSH(dbp->dbenv,
                            cp, h, indx, lock, lock_mode, ret);
                        if (ret != 0)
                                goto err;

                        lock_mode = DB_LOCK_WRITE;
                        if ((ret =
                            CDB___db_lget(dbc, 0, pg, lock_mode, 0, &lock)) != 0)
                                goto err;
                } else {
                        /*
                         * Decide if we want to return a reference to the next
                         * page in the return stack.  If so, lock it and never
                         * unlock it.
                         */
                        if ((LF_ISSET(S_PARENT) &&
                            (u_int8_t)(stop + 1) >= (u_int8_t)(h->level - 1)) ||
                            (h->level - 1) == LEAFLEVEL)
                                stack = 1;

                        (void)CDB_memp_fput(dbp->mpf, h, 0);

                        lock_mode = stack &&
                            LF_ISSET(S_WRITE) ? DB_LOCK_WRITE : DB_LOCK_READ;
                        if ((ret = CDB___db_lget(dbc,
                            LCK_COUPLE, pg, lock_mode, 0, &lock)) != 0) {
                                /*
                                 * If we fail, discard the lock we held.  This
                                 * is OK because this only happens when we are
                                 * descending the tree holding read-locks.
                                 */
                                __LPUT(dbc, lock);
                                goto err;
                        }
                }
                if ((ret = CDB_memp_fget(dbp->mpf, &pg, 0, &h)) != 0)
                        goto err;
        }
        /* NOTREACHED */

found:  *exactp = 1;

        /*
         * If we're trying to calculate the record number, add in the
         * offset on this page and correct for the fact that records
         * in the tree are 0-based.
         */
        if (recnop != NULL)
                *recnop = recno + (indx / P_INDX) + 1;

        /*
         * If we got here, we know that we have a Btree leaf or off-page
         * duplicates page.  If it's a Btree leaf page, we have to handle
         * on-page duplicates.
         *
         * If there are duplicates, go to the first/last one.  This is
         * safe because we know that we're not going to leave the page,
         * all duplicate sets that are not on overflow pages exist on a
         * single leaf page.
         */
        if (TYPE(h) == P_LBTREE) {
                if (LF_ISSET(S_DUPLAST))
                        while (indx < (db_indx_t)(NUM_ENT(h) - P_INDX) &&
                            h->inp[indx] == h->inp[indx + P_INDX])
                                indx += P_INDX;
                else
                        while (indx > 0 &&
                            h->inp[indx] == h->inp[indx - P_INDX])
                                indx -= P_INDX;
        }

        /*
         * Now check if we are allowed to return deleted items; if not, then
         * find the next (or previous) non-deleted duplicate entry.  (We do
         * not move from the original found key on the basis of the S_DELNO
         * flag.)
         */
        if (LF_ISSET(S_DELNO)) {
                deloffset = TYPE(h) == P_LBTREE ? O_INDX : 0;
                if (LF_ISSET(S_DUPLAST))
                        while (B_DISSET(GET_BKEYDATA(
                            h, indx + deloffset)->type) && indx > 0 &&
                            h->inp[indx] == h->inp[indx - adjust])
                                indx -= adjust;
                else
                        while (B_DISSET(GET_BKEYDATA(
                            h, indx + deloffset)->type) &&
                            indx < (db_indx_t)(NUM_ENT(h) - adjust) &&
                            h->inp[indx] == h->inp[indx + adjust])
                                indx += adjust;

                /*
                 * If we weren't able to find a non-deleted duplicate, return
                 * DB_NOTFOUND.
                 */
                if (B_DISSET(GET_BKEYDATA(h, indx + deloffset)->type))
                        goto notfound;
        }

        if (LF_ISSET(S_STK_ONLY)) {
                BT_STK_NUM(dbp->dbenv, cp, h, indx, ret);
                __LPUT(dbc, lock);
                (void)CDB_memp_fput(dbp->mpf, h, 0);
        } else {
                BT_STK_ENTER(dbp->dbenv, cp, h, indx, lock, lock_mode, ret);
                if (ret != 0)
                        goto err;
        }
        return (0);

notfound:
        /* Keep the page locked for serializability. */
        (void)CDB_memp_fput(dbp->mpf, h, 0);
        (void)__TLPUT(dbc, lock);
        ret = DB_NOTFOUND;

err:    if (cp->csp > cp->sp) {
                BT_STK_POP(cp);
                CDB___bam_stkrel(dbc, 0);
        }
        return (ret);
}

/*
 * CDB___bam_stkrel --
 *      Release all pages currently held in the stack.
 *
 * PUBLIC: int CDB___bam_stkrel __P((DBC *, u_int32_t));
 */
int
CDB___bam_stkrel(dbc, flags)
        DBC *dbc;
        u_int32_t flags;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        EPG *epg;
        int ret, t_ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;

        /*
         * Release inner pages first.
         *
         * The caller must be sure that setting STK_NOLOCK will not effect
         * either serializability or recoverability.
         */
        for (ret = 0, epg = cp->sp; epg <= cp->csp; ++epg) {
                if (epg->page != NULL) {
                        if (LF_ISSET(STK_CLRDBC) && cp->page == epg->page) {
                                cp->page = NULL;
                                cp->lock.off = LOCK_INVALID;
                        }
                        if ((t_ret = CDB_memp_fput(
                            dbp->mpf, epg->page, 0)) != 0 && ret == 0)
                                ret = t_ret;
                }
                if (epg->lock.off != LOCK_INVALID) {
                        if (LF_ISSET(STK_NOLOCK))
                                (void)__LPUT(dbc, epg->lock);
                        else
                                (void)__TLPUT(dbc, epg->lock);
                }
        }

        /* Clear the stack, all pages have been released. */
        BT_STK_CLR(cp);

        return (ret);
}

/*
 * CDB___bam_stkgrow --
 *      Grow the stack.
 *
 * PUBLIC: int CDB___bam_stkgrow __P((DB_ENV *, BTREE_CURSOR *));
 */
int
CDB___bam_stkgrow(dbenv, cp)
        DB_ENV *dbenv;
        BTREE_CURSOR *cp;
{
        EPG *p;
        size_t entries;
        int ret;

        entries = cp->esp - cp->sp;

        if ((ret = CDB___os_calloc(dbenv, entries * 2, sizeof(EPG), &p)) != 0)
                return (ret);
        memcpy(p, cp->sp, entries * sizeof(EPG));
        if (cp->sp != cp->stack)
                CDB___os_free(cp->sp, entries * sizeof(EPG));
        cp->sp = p;
        cp->csp = p + entries;
        cp->esp = p + entries * 2;
        return (0);
}

---