xref: /csrg-svn/lib/libc/db/btree/bt_get.c (revision 57989)

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Mike Olson.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)bt_get.c	5.8 (Berkeley) 02/14/93";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <errno.h>
#include <stddef.h>
#include <stdio.h>

#include <db.h>
#include "btree.h"

/*
 * __BT_GET -- Get a record from the btree.
 *
 * Parameters:
 *	dbp:	pointer to access method
 *	key:	key to find
 *	data:	data to return
 *	flag:	currently unused
 *
 * Returns:
 *	RET_ERROR, RET_SUCCESS and RET_SPECIAL if the key not found.
 */
int
__bt_get(dbp, key, data, flags)
	const DB *dbp;
	const DBT *key;
	DBT *data;
	u_int flags;
{
	BTREE *t;
	EPG *e;
	int exact, status;

	if (flags) {
		errno = EINVAL;
		return (RET_ERROR);
	}
	t = dbp->internal;
	if ((e = __bt_search(t, key, &exact)) == NULL)
		return (RET_ERROR);
	if (!exact) {
		mpool_put(t->bt_mp, e->page, 0);
		return (RET_SPECIAL);
	}

	/*
	 * A special case is if we found the record but it's flagged for
	 * deletion.  In this case, we want to find another record with the
	 * same key, if it exists.  Rather than look around the tree we call
	 * __bt_first and have it redo the search, as __bt_first will not
	 * return keys marked for deletion.  Slow, but should never happen.
	 */
	if (ISSET(t, BTF_DELCRSR) && e->page->pgno == t->bt_bcursor.pgno &&
	    e->index == t->bt_bcursor.index) {
		mpool_put(t->bt_mp, e->page, 0);
		if ((e = __bt_first(t, key, &exact)) == NULL)
			return (RET_ERROR);
		if (!exact)
			return (RET_SPECIAL);
	}

	status = __bt_ret(t, e, NULL, data);
	mpool_put(t->bt_mp, e->page, 0);
	return (status);
}

/*
 * __BT_FIRST -- Find the first entry.
 *
 * Parameters:
 *	t:	the tree
 *	key:	the key
 *
 * Returns:
 *	The first entry in the tree greater than or equal to key.
 */
EPG *
__bt_first(t, key, exactp)
	BTREE *t;
	const DBT *key;
	int *exactp;
{
	register PAGE *h;
	register EPG *e;
	EPG save;
	pgno_t cpgno, pg;
	indx_t cindex;
	int found;

	/*
	 * Find any matching record; __bt_search pins the page.  Only exact
	 * matches are tricky, otherwise just return the location of the key
	 * if it were to be inserted into the tree.
	 */
	if ((e = __bt_search(t, key, exactp)) == NULL)
		return (NULL);
	if (!*exactp)
		return (e);

	if (ISSET(t, BTF_DELCRSR)) {
		cpgno = t->bt_bcursor.pgno;
		cindex = t->bt_bcursor.index;
	} else {
		cpgno = P_INVALID;
		cindex = 0;		/* GCC thinks it's uninitialized. */
	}

	/*
	 * Walk backwards, skipping empty pages, as long as the entry matches
	 * and there are keys left in the tree.  Save a copy of each match in
	 * case we go too far.  A special case is that we don't return a match
	 * on records that the cursor references that have already been flagged
	 * for deletion.
	 */
	save = *e;
	h = e->page;
	found = 0;
	do {
		if (cpgno != h->pgno || cindex != e->index) {
			if (save.page->pgno != e->page->pgno) {
				mpool_put(t->bt_mp, save.page, 0);
				save = *e;
			} else
				save.index = e->index;
			found = 1;
		}
		/*
		 * Make a special effort not to unpin the page the last (or
		 * original) match was on, but also make sure it's unpinned
		 * if an error occurs.
		 */
		while (e->index == 0) {
			if (h->prevpg == P_INVALID)
				goto done1;
			if (h->pgno != save.page->pgno)
				mpool_put(t->bt_mp, h, 0);
			if ((h = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) {
				if (h->pgno == save.page->pgno)
					mpool_put(t->bt_mp, save.page, 0);
				return (NULL);
			}
			e->page = h;
			e->index = NEXTINDEX(h);
		}
		--e->index;
	} while (__bt_cmp(t, key, e) == 0);

	/*
	 * Reach here with the last page that was looked at pinned, which may
	 * or may not be the same as the last (or original) match page.  If
	 * it's not useful, release it.
	 */
done1:	if (h->pgno != save.page->pgno)
		mpool_put(t->bt_mp, h, 0);

	/*
	 * If still haven't found a record, the only possibility left is the
	 * next one.  Move forward one slot, skipping empty pages and check.
	 */
	if (!found) {
		h = save.page;
		if (++save.index == NEXTINDEX(h)) {
			do {
				pg = h->nextpg;
				mpool_put(t->bt_mp, h, 0);
				if (pg == P_INVALID) {
					*exactp = 0;
					return (e);
				}
				if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
					return (NULL);
			} while ((save.index = NEXTINDEX(h)) == 0);
			save.page = h;
		}
		if (__bt_cmp(t, key, &save) != 0) {
			*exactp = 0;
			return (e);
		}
	}
	*e = save;
	*exactp = 1;
	return (e);
}