bt_delete.c

Go to the documentation of this file.

/*-
 * 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);
}