db/btree/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);
}