bt_delete.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_delete.c 8.13 (Berkeley) 7/28/94";
#endif /* LIBC_SCCS and not lint */
 
#include <sys/types.h>
 
#include <errno.h>
#include <stdio.h>
#include <string.h>
 
#include "../include/db.h"
#include "btree.h"
 
static int __bt_bdelete __P((BTREE *, const DBT *));
static int __bt_curdel __P((BTREE *, const DBT *, PAGE *, u_int));
static int __bt_pdelete __P((BTREE *, PAGE *));
static int __bt_relink __P((BTREE *, PAGE *));
static int __bt_stkacq __P((BTREE *, PAGE **, CURSOR *));
 
/*
 * __bt_delete
 *  Delete the item(s) referenced by a key.
 *
 * Return RET_SPECIAL if the key is not found.
 */
int
__bt_delete(dbp, key, flags)
    const DB *dbp;
    const DBT *key;
    u_int flags;
{
    BTREE *t;
    CURSOR *c;
    PAGE *h;
    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;
    }
 
    /* Check for change to a read-only tree. */
    if (F_ISSET(t, B_RDONLY)) {
        errno = EPERM;
        return (RET_ERROR);
    }
 
    switch (flags) {
    case 0:
        status = __bt_bdelete(t, key);
        break;
    case R_CURSOR:
        /*
         * If flags is R_CURSOR, delete the cursor.  Must already
         * have started a scan and not have already deleted it.
         */
        c = &t->bt_cursor;
        if (F_ISSET(c, CURS_INIT)) {
            if (F_ISSET(c, CURS_ACQUIRE | CURS_AFTER | CURS_BEFORE))
                return (RET_SPECIAL);
            if ((h = mpool_get(t->bt_mp, c->pg.pgno, 0)) == NULL)
                return (RET_ERROR);
 
            /*
             * If the page is about to be emptied, we'll need to
             * delete it, which means we have to acquire a stack.
             */
            if (NEXTINDEX(h) == 1)
                if (__bt_stkacq(t, &h, &t->bt_cursor))
                    return (RET_ERROR);
 
            status = __bt_dleaf(t, NULL, h, c->pg.index);
 
            if (NEXTINDEX(h) == 0 && status == RET_SUCCESS) {
                if (__bt_pdelete(t, h))
                    return (RET_ERROR);
            } else
                mpool_put(t->bt_mp,
                    h, status == RET_SUCCESS ? MPOOL_DIRTY : 0);
            break;
        }
        /* FALLTHROUGH */
    default:
        errno = EINVAL;
        return (RET_ERROR);
    }
    if (status == RET_SUCCESS)
        F_SET(t, B_MODIFIED);
    return (status);
}
 
/*
 * __bt_stkacq --
 *  Acquire a stack so we can delete a cursor entry.
 *
 * Parameters:
 *    t:    tree
 *   hp:    pointer to current, pinned PAGE pointer
 *    c:    pointer to the cursor
 *
 * Returns:
 *  0 on success, 1 on failure
 */
static int
__bt_stkacq(t, hp, c)
    BTREE *t;
    PAGE **hp;
    CURSOR *c;
{
    BINTERNAL *bi;
    EPG *e;
    EPGNO *parent;
    PAGE *h;
    indx_t idx = 0;
    pgno_t pgno;
    recno_t nextpg, prevpg;
    int exact, level;
 
    /*
     * Find the first occurrence of the key in the tree.  Toss the
     * currently locked page so we don't hit an already-locked page.
     */
    h = *hp;
    mpool_put(t->bt_mp, h, 0);
    if ((e = __bt_search(t, &c->key, &exact)) == NULL)
        return (1);
    h = e->page;
 
    /* See if we got it in one shot. */
    if (h->pgno == c->pg.pgno)
        goto ret;
 
    /*
     * Move right, looking for the page.  At each move we have to move
     * up the stack until we don't have to move to the next page.  If
     * we have to change pages at an internal level, we have to fix the
     * stack back up.
     */
    while (h->pgno != c->pg.pgno) {
        if ((nextpg = h->nextpg) == P_INVALID)
            break;
        mpool_put(t->bt_mp, h, 0);
 
        /* Move up the stack. */
        for (level = 0; (parent = BT_POP(t)) != NULL; ++level) {
            /* Get the parent page. */
            if ((h = mpool_get(t->bt_mp, parent->pgno, 0)) == NULL)
                return (1);
 
            /* Move to the next index. */
            if (parent->index != NEXTINDEX(h) - 1) {
                idx = parent->index + 1;
                BT_PUSH(t, h->pgno, idx);
                break;
            }
            mpool_put(t->bt_mp, h, 0);
        }
 
        /* Restore the stack. */
        while (level--) {
            /* Push the next level down onto the stack. */
            bi = GETBINTERNAL(h, idx);
            pgno = bi->pgno;
            BT_PUSH(t, pgno, 0);
 
            /* Lose the currently pinned page. */
            mpool_put(t->bt_mp, h, 0);
 
            /* Get the next level down. */
            if ((h = mpool_get(t->bt_mp, pgno, 0)) == NULL)
                return (1);
            idx = 0;
        }
        mpool_put(t->bt_mp, h, 0);
        if ((h = mpool_get(t->bt_mp, nextpg, 0)) == NULL)
            return (1);
    }
 
    if (h->pgno == c->pg.pgno)
        goto ret;
 
    /* Reacquire the original stack. */
    mpool_put(t->bt_mp, h, 0);
    if ((e = __bt_search(t, &c->key, &exact)) == NULL)
        return (1);
    h = e->page;
 
    /*
     * Move left, looking for the page.  At each move we have to move
     * up the stack until we don't have to change pages to move to the
     * next page.  If we have to change pages at an internal level, we
     * have to fix the stack back up.
     */
    while (h->pgno != c->pg.pgno) {
        if ((prevpg = h->prevpg) == P_INVALID)
            break;
        mpool_put(t->bt_mp, h, 0);
 
        /* Move up the stack. */
        for (level = 0; (parent = BT_POP(t)) != NULL; ++level) {
            /* Get the parent page. */
            if ((h = mpool_get(t->bt_mp, parent->pgno, 0)) == NULL)
                return (1);
 
            /* Move to the next index. */
            if (parent->index != 0) {
                idx = parent->index - 1;
                BT_PUSH(t, h->pgno, idx);
                break;
            }
            mpool_put(t->bt_mp, h, 0);
        }
 
        /* Restore the stack. */
        while (level--) {
            /* Push the next level down onto the stack. */
            bi = GETBINTERNAL(h, idx);
            pgno = bi->pgno;
 
            /* Lose the currently pinned page. */
            mpool_put(t->bt_mp, h, 0);
 
            /* Get the next level down. */
            if ((h = mpool_get(t->bt_mp, pgno, 0)) == NULL)
                return (1);
 
            idx = NEXTINDEX(h) - 1;
            BT_PUSH(t, pgno, idx);
        }
        mpool_put(t->bt_mp, h, 0);
        if ((h = mpool_get(t->bt_mp, prevpg, 0)) == NULL)
            return (1);
    }
 
 
ret:    mpool_put(t->bt_mp, h, 0);
    return ((*hp = mpool_get(t->bt_mp, c->pg.pgno, 0)) == NULL);
}
 
/*
 * __bt_bdelete --
 *  Delete all key/data pairs matching the specified key.
 *
 * Parameters:
 *    t:    tree
 *  key:    key to delete
 *
 * Returns:
 *  RET_ERROR, RET_SUCCESS and RET_SPECIAL if the key not found.
 */
static int
__bt_bdelete(t, key)
    BTREE *t;
    const DBT *key;
{
    EPG *e;
    PAGE *h;
    int deleted, exact, redo;
 
    deleted = 0;
 
    /* Find any matching record; __bt_search pins the page. */
loop:   if ((e = __bt_search(t, key, &exact)) == NULL)
        return (deleted ? RET_SUCCESS : RET_ERROR);
    if (!exact) {
        mpool_put(t->bt_mp, e->page, 0);
        return (deleted ? RET_SUCCESS : RET_SPECIAL);
    }
 
    /*
     * Delete forward, then delete backward, from the found key.  If
     * there are duplicates and we reach either side of the page, do
     * the key search again, so that we get them all.
     */
    redo = 0;
    h = e->page;
    do {
        if (__bt_dleaf(t, key, h, e->index)) {
            mpool_put(t->bt_mp, h, 0);
            return (RET_ERROR);
        }
        if (F_ISSET(t, B_NODUPS)) {
            if (NEXTINDEX(h) == 0) {
                if (__bt_pdelete(t, h))
                    return (RET_ERROR);
            } else
                mpool_put(t->bt_mp, h, MPOOL_DIRTY);
            return (RET_SUCCESS);
        }
        deleted = 1;
    } while (e->index < NEXTINDEX(h) && __bt_cmp(t, key, e) == 0);
 
    /* Check for right-hand edge of the page. */
    if (e->index == NEXTINDEX(h))
        redo = 1;
 
    /* Delete from the key to the beginning of the page. */
    while (e->index-- > 0) {
        if (__bt_cmp(t, key, e) != 0)
            break;
        if (__bt_dleaf(t, key, h, e->index) == RET_ERROR) {
            mpool_put(t->bt_mp, h, 0);
            return (RET_ERROR);
        }
        if (e->index == 0)
            redo = 1;
    }
 
    /* Check for an empty page. */
    if (NEXTINDEX(h) == 0) {
        if (__bt_pdelete(t, h))
            return (RET_ERROR);
        goto loop;
    }
 
    /* Put the page. */
    mpool_put(t->bt_mp, h, MPOOL_DIRTY);
 
    if (redo)
        goto loop;
    return (RET_SUCCESS);
}
 
/*
 * __bt_pdelete --
 *  Delete a single page from the tree.
 *
 * Parameters:
 *  t:  tree
 *  h:  leaf page
 *
 * Returns:
 *  RET_SUCCESS, RET_ERROR.
 *
 * Side-effects:
 *  mpool_put's the page
 */
static int
__bt_pdelete(t, h)
    BTREE *t;
    PAGE *h;
{
    BINTERNAL *bi;
    PAGE *pg;
    EPGNO *parent;
    indx_t cnt, idx, *ip, offset;
    u_int32_t nksize;
    char *from;
 
    /*
     * Walk the parent page stack -- a LIFO stack of the pages that were
     * traversed when we searched for the page where the delete occurred.
     * Each stack entry is a page number and a page index offset.  The
     * offset is for the page traversed on the search.  We've just deleted
     * a page, so we have to delete the key from the parent page.
     *
     * If the delete from the parent page makes it empty, this process may
     * continue all the way up the tree.  We stop if we reach the root page
     * (which is never deleted, it's just not worth the effort) or if the
     * delete does not empty the page.
     */
    while ((parent = BT_POP(t)) != NULL) {
        /* Get the parent page. */
        if ((pg = mpool_get(t->bt_mp, parent->pgno, 0)) == NULL)
            return (RET_ERROR);
 
        idx = parent->index;
        bi = GETBINTERNAL(pg, idx);
 
        /* Free any overflow pages. */
        if (bi->flags & P_BIGKEY &&
            __ovfl_delete(t, bi->bytes) == RET_ERROR) {
            mpool_put(t->bt_mp, pg, 0);
            return (RET_ERROR);
        }
 
        /*
         * Free the parent if it has only the one key and it's not the
         * root page. If it's the rootpage, turn it back into an empty
         * leaf page.
         */
        if (NEXTINDEX(pg) == 1) {
            if (pg->pgno == P_ROOT) {
                pg->lower = BTDATAOFF;
                pg->upper = t->bt_psize;
                pg->flags = P_BLEAF;
            } else {
                if (__bt_relink(t, pg) || __bt_free(t, pg))
                    return (RET_ERROR);
                continue;
            }
        } else {
            /* Pack remaining key items at the end of the page. */
            nksize = NBINTERNAL(bi->ksize);
            from = (char *)pg + pg->upper;
            memmove(from + nksize, from, (char *)bi - from);
            pg->upper += nksize;
 
            /* Adjust indices' offsets, shift the indices down. */
            offset = pg->linp[idx];
            for (cnt = idx, ip = &pg->linp[0]; cnt--; ++ip)
                if (ip[0] < offset)
                    ip[0] += nksize;
            for (cnt = NEXTINDEX(pg) - idx; --cnt; ++ip)
                ip[0] = ip[1] < offset ? ip[1] + nksize : ip[1];
            pg->lower -= sizeof(indx_t);
        }
 
        mpool_put(t->bt_mp, pg, MPOOL_DIRTY);
        break;
    }
 
    /* Free the leaf page, as long as it wasn't the root. */
    if (h->pgno == P_ROOT) {
        mpool_put(t->bt_mp, h, MPOOL_DIRTY);
        return (RET_SUCCESS);
    }
    return (__bt_relink(t, h) || __bt_free(t, h));
}
 
/*
 * __bt_dleaf --
 *  Delete a single record from a leaf page.
 *
 * Parameters:
 *  t:  tree
 *    key:  referenced key
 *  h:  page
 *  index:  index on page to delete
 *
 * Returns:
 *  RET_SUCCESS, RET_ERROR.
 */
int
__bt_dleaf(t, key, h, idx)
    BTREE *t;
    const DBT *key;
    PAGE *h;
    u_int idx;
{
    BLEAF *bl;
    indx_t cnt, *ip, offset;
    u_int32_t nbytes;
    void *to;
    char *from;
 
    /* If this record is referenced by the cursor, delete the cursor. */
    if (F_ISSET(&t->bt_cursor, CURS_INIT) &&
        !F_ISSET(&t->bt_cursor, CURS_ACQUIRE) &&
        t->bt_cursor.pg.pgno == h->pgno && t->bt_cursor.pg.index == idx &&
        __bt_curdel(t, key, h, idx))
        return (RET_ERROR);
 
    /* If the entry uses overflow pages, make them available for reuse. */
    to = bl = GETBLEAF(h, idx);
    if (bl->flags & P_BIGKEY && __ovfl_delete(t, bl->bytes) == RET_ERROR)
        return (RET_ERROR);
    if (bl->flags & P_BIGDATA &&
        __ovfl_delete(t, bl->bytes + bl->ksize) == RET_ERROR)
        return (RET_ERROR);
 
    /* Pack the remaining key/data items at the end of the page. */
    nbytes = NBLEAF(bl);
    from = (char *)h + h->upper;
    memmove(from + nbytes, from, (char *)to - from);
    h->upper += nbytes;
 
    /* Adjust the indices' offsets, shift the indices down. */
    offset = h->linp[idx];
    for (cnt = idx, ip = &h->linp[0]; cnt--; ++ip)
        if (ip[0] < offset)
            ip[0] += nbytes;
    for (cnt = NEXTINDEX(h) - idx; --cnt; ++ip)
        ip[0] = ip[1] < offset ? ip[1] + nbytes : ip[1];
    h->lower -= sizeof(indx_t);
 
    /* If the cursor is on this page, adjust it as necessary. */
    if (F_ISSET(&t->bt_cursor, CURS_INIT) &&
        !F_ISSET(&t->bt_cursor, CURS_ACQUIRE) &&
        t->bt_cursor.pg.pgno == h->pgno && t->bt_cursor.pg.index > idx)
        --t->bt_cursor.pg.index;
 
    return (RET_SUCCESS);
}
 
/*
 * __bt_curdel --
 *  Delete the cursor.
 *
 * Parameters:
 *  t:  tree
 *    key:  referenced key (or NULL)
 *  h:  page
 *  index:  index on page to delete
 *
 * Returns:
 *  RET_SUCCESS, RET_ERROR.
 */
static int
__bt_curdel(t, key, h, idx)
    BTREE *t;
    const DBT *key;
    PAGE *h;
    u_int idx;
{
    CURSOR *c;
    EPG e;
    PAGE *pg;
    int curcopy, status;
 
    /*
     * If there are duplicates, move forward or backward to one.
     * Otherwise, copy the key into the cursor area.
     */
    c = &t->bt_cursor;
    F_CLR(c, CURS_AFTER | CURS_BEFORE | CURS_ACQUIRE);
 
    curcopy = 0;
    if (!F_ISSET(t, B_NODUPS)) {
        /*
         * We're going to have to do comparisons.  If we weren't
         * provided a copy of the key, i.e. the user is deleting
         * the current cursor position, get one.
         */
        if (key == NULL) {
            e.page = h;
            e.index = idx;
            if ((status = __bt_ret(t, &e,
                &c->key, &c->key, NULL, NULL, 1)) != RET_SUCCESS)
                return (status);
            curcopy = 1;
            key = &c->key;
        }
        /* Check previous key, if not at the beginning of the page. */
        if (idx > 0) {
            e.page = h;
            e.index = idx - 1;
            if (__bt_cmp(t, key, &e) == 0) {
                F_SET(c, CURS_BEFORE);
                goto dup2;
            }
        }
        /* Check next key, if not at the end of the page. */
        if (idx < NEXTINDEX(h) - 1) {
            e.page = h;
            e.index = idx + 1;
            if (__bt_cmp(t, key, &e) == 0) {
                F_SET(c, CURS_AFTER);
                goto dup2;
            }
        }
        /* Check previous key if at the beginning of the page. */
        if (idx == 0 && h->prevpg != P_INVALID) {
            if ((pg = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
                return (RET_ERROR);
            e.page = pg;
            e.index = NEXTINDEX(pg) - 1;
            if (__bt_cmp(t, key, &e) == 0) {
                F_SET(c, CURS_BEFORE);
                goto dup1;
            }
            mpool_put(t->bt_mp, pg, 0);
        }
        /* Check next key if at the end of the page. */
        if (idx == NEXTINDEX(h) - 1 && h->nextpg != P_INVALID) {
            if ((pg = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
                return (RET_ERROR);
            e.page = pg;
            e.index = 0;
            if (__bt_cmp(t, key, &e) == 0) {
                F_SET(c, CURS_AFTER);
dup1:               mpool_put(t->bt_mp, pg, 0);
dup2:               c->pg.pgno = e.page->pgno;
                c->pg.index = e.index;
                return (RET_SUCCESS);
            }
            mpool_put(t->bt_mp, pg, 0);
        }
    }
    e.page = h;
    e.index = idx;
    if (curcopy || (status =
        __bt_ret(t, &e, &c->key, &c->key, NULL, NULL, 1)) == RET_SUCCESS) {
        F_SET(c, CURS_ACQUIRE);
        return (RET_SUCCESS);
    }
    return (status);
}
 
/*
 * __bt_relink --
 *  Link around a deleted page.
 *
 * Parameters:
 *  t:  tree
 *  h:  page to be deleted
 */
static int
__bt_relink(t, h)
    BTREE *t;
    PAGE *h;
{
    PAGE *pg;
 
    if (h->nextpg != P_INVALID) {
        if ((pg = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
            return (RET_ERROR);
        pg->prevpg = h->prevpg;
        mpool_put(t->bt_mp, pg, MPOOL_DIRTY);
    }
    if (h->prevpg != P_INVALID) {
        if ((pg = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
            return (RET_ERROR);
        pg->nextpg = h->nextpg;
        mpool_put(t->bt_mp, pg, MPOOL_DIRTY);
    }
    return (0);
}