src/db/db_meta.c

/*-
 * Copyright (c) 1996, 2020 Oracle and/or its affiliates.  All rights reserved.
 *
 * See the file LICENSE for license information.
 */
/*
 * 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.
 *
 * $Id$
 */

#include "db_config.h"

#include "db_int.h"
#include "dbinc/db_page.h"
#include "dbinc/lock.h"
#include "dbinc/log.h"
#include "dbinc/mp.h"
#include "dbinc/txn.h"
#include "dbinc/db_am.h"
#include "dbinc/hash.h"

static void __db_init_meta __P((DB *, void *, db_pgno_t, u_int32_t));
#ifdef HAVE_FTRUNCATE
static int  __db_pglistcmp __P((const void *, const void *));
static int  __db_truncate_freelist __P((DBC *, DBMETA *,
      PAGE *, db_pgno_t *, u_int32_t, u_int32_t));
#endif

/*
 * __db_init_meta --
 *	Helper function for __db_new that initializes the important fields in
 * a meta-data page (used instead of P_INIT).  We need to make sure that we
 * retain the page number and LSN of the existing page.
 */
static void
__db_init_meta(dbp, p, pgno, pgtype)
	DB *dbp;
	void *p;
	db_pgno_t pgno;
	u_int32_t pgtype;
{
	DBMETA *meta;
	DB_LSN save_lsn;

	meta = (DBMETA *)p;
	save_lsn = meta->lsn;
	memset(meta, 0, sizeof(DBMETA));
	meta->lsn = save_lsn;
	meta->pagesize = dbp->pgsize;
	if (F_ISSET(dbp, DB_AM_CHKSUM))
		FLD_SET(meta->metaflags, DBMETA_CHKSUM);
	meta->pgno = pgno;
	meta->type = (u_int8_t)pgtype;
}

/*
 * __db_new --
 *	Get a new page, preferably from the freelist.
 *
 * PUBLIC: int __db_new __P((DBC *, u_int32_t, DB_LOCK *, PAGE **));
 */
int
__db_new(dbc, type, lockp, pagepp)
	DBC *dbc;
	u_int32_t type;
	DB_LOCK *lockp;
	PAGE **pagepp;
{
	DB *dbp;
	DBMETA *meta;
	DB_LOCK metalock;
	DB_LSN lsn;
	DB_MPOOLFILE *mpf;
	ENV *env;
	PAGE *h;
	db_pgno_t last, *list, pgno, newnext;
	int extend, hash, ret;

	COMPQUIET(last, 0);

	meta = NULL;
	dbp = dbc->dbp;
	env = dbp->env;
	mpf = dbp->mpf;
	h = NULL;
	newnext = PGNO_INVALID;
	if (lockp != NULL)
		LOCK_INIT(*lockp);

	hash = 0;
	ret = 0;
	LOCK_INIT(metalock);

#ifdef HAVE_HASH
	if (dbp->type == DB_HASH) {
		if ((ret = __ham_return_meta(dbc, DB_MPOOL_DIRTY, &meta)) != 0)
			goto err;
		if (meta != NULL)
			hash = 1;
	}
#endif
	if (meta == NULL) {
		pgno = PGNO_BASE_MD;
		if ((ret = __db_lget(dbc,
		    LCK_ALWAYS, pgno, DB_LOCK_WRITE, 0, &metalock)) != 0)
			goto err;
		if ((ret = __memp_fget(mpf, &pgno, dbc->thread_info, dbc->txn,
		    DB_MPOOL_DIRTY, &meta)) != 0)
			goto err;
	}

	last = meta->last_pgno;
	if (meta->free == PGNO_INVALID) {
		if (FLD_ISSET(type, P_DONTEXTEND)) {
			*pagepp = NULL;
			goto err;
		}
		last = pgno = meta->last_pgno + 1;
		ZERO_LSN(lsn);
		extend = 1;
	} else {
		pgno = meta->free;
		/*
		 * Lock the new page.  Do this here because we must do it
		 * before getting the page and the caller may need the lock
		 * to keep readers from seeing the page before the transaction
		 * commits.  We can do this because no one will hold a free
		 * page locked.
		 */
		if (lockp != NULL && (ret =
		     __db_lget(dbc, 0, pgno, DB_LOCK_WRITE, 0, lockp)) != 0)
			goto err;
		if ((ret = __memp_fget(mpf, &pgno, dbc->thread_info, dbc->txn,
		    DB_MPOOL_DIRTY, &h)) != 0)
			goto err;

		/*
		 * We want to take the first page off the free list and
		 * then set meta->free to the that page's next_pgno, but
		 * we need to log the change first.
		 */
		newnext = h->next_pgno;
		lsn = h->lsn;
		extend = 0;
		DB_ASSERT(env, TYPE(h) == P_INVALID);

		if (TYPE(h) != P_INVALID) {
			__db_errx(env, DB_STR_A("0689",
			    "%s page %lu is on free list with type %lu",
			    "%s %lu %lu"), dbp->fname, (u_long)PGNO(h),
			    (u_long)TYPE(h));
			return (__env_panic(env, EINVAL));
		}

	}

	FLD_CLR(type, P_DONTEXTEND);

	/*
	 * Log the allocation before fetching the new page.  If we
	 * don't have room in the log then we don't want to tell
	 * mpool to extend the file.
	 */
	if (DBC_LOGGING(dbc)) {
		if ((ret = __db_pg_alloc_log(dbp, dbc->txn, &LSN(meta), 0,
		    &LSN(meta), PGNO_BASE_MD, &lsn,
		    pgno, (u_int32_t)type, newnext, meta->last_pgno)) != 0)
			goto err;
	} else
		LSN_NOT_LOGGED(LSN(meta));

	meta->free = newnext;

	if (extend == 1) {
		if (lockp != NULL && (ret =
		     __db_lget(dbc, 0, pgno, DB_LOCK_WRITE, 0, lockp)) != 0)
			goto err;
		if ((ret = __memp_fget(mpf, &pgno, dbc->thread_info, dbc->txn,
		    DB_MPOOL_NEW, &h)) != 0)
			goto err;
		DB_ASSERT(env, last == pgno);
		meta->last_pgno = pgno;
		ZERO_LSN(h->lsn);
		h->pgno = pgno;

		/*
		 * If the file was extended for the first time in this
		 * transaction, set the MPOOLFILE's file extension
		 * watermark.
		 */
		__txn_add_fe_watermark(dbc->txn, dbp, h->pgno);

	}
	LSN(h) = LSN(meta);

	if (hash == 0 && (ret = __memp_fput(mpf,
	    dbc->thread_info, meta, dbc->priority)) != 0)
		goto err;
	meta = NULL;

	switch (type) {
		case P_BTREEMETA:
		case P_HASHMETA:
		case P_QAMMETA:
			__db_init_meta(dbp, h, h->pgno, type);
			break;
		default:
			P_INIT(h, dbp->pgsize,
			    h->pgno, PGNO_INVALID, PGNO_INVALID, 0, type);
			break;
	}

	/* Fix up the sorted free list if necessary. */
#ifdef HAVE_FTRUNCATE
	if (extend == 0) {
		u_int32_t nelems = 0;

		if ((ret = __memp_get_freelist(dbp->mpf, &nelems, &list)) != 0)
			goto err;
		if (nelems != 0) {
			DB_ASSERT(env, h->pgno == list[0]);
			memmove(list, &list[1], (nelems - 1) * sizeof(*list));
			if ((ret = __memp_extend_freelist(
			    dbp->mpf, nelems - 1, &list)) != 0)
				goto err;
		}
	}
#else
	COMPQUIET(list, NULL);
#endif

	if ((ret = __TLPUT(dbc, metalock)) != 0)
		return (ret);
	*pagepp = h;
	PERFMON6(env, alloc, new, dbp->fname, dbp->dname, pgno, type, h, 0);
	return (0);

err:	if (h != NULL)
		(void)__memp_fput(mpf, dbc->thread_info, h, dbc->priority);
	if (meta != NULL && hash == 0)
		(void)__memp_fput(mpf, dbc->thread_info, meta, dbc->priority);
	(void)__TLPUT(dbc, metalock);
	if (lockp != NULL)
		(void)__LPUT(dbc, *lockp);
	/* Failure return - report 0 pgno, null page address. */
	PERFMON6(env, alloc, new, dbp->fname, dbp->dname, 0, type, NULL, ret);
	return (ret);
}

/*
 * __db_free --
 *	Add a page to the head of the freelist.
 *
 * PUBLIC: int __db_free __P((DBC *, PAGE *, u_int32_t));
 */
int
__db_free(dbc, h, flags)
	DBC *dbc;
	PAGE *h;
	u_int32_t flags;
{
	DB *dbp;
	DBMETA *meta;
	DBT ddbt, ldbt;
	DB_LOCK metalock;
	DB_LSN *lsnp;
	DB_MPOOLFILE *mpf;
	PAGE *prev;
	db_pgno_t last_pgno, next_pgno, pgno, prev_pgno;
	u_int32_t lflag;
	int hash, ret, t_ret;
#ifdef HAVE_FTRUNCATE
	db_pgno_t *list, *lp;
	u_int32_t nelem, position, start;
	int do_truncate;
#endif

	dbp = dbc->dbp;
	mpf = dbp->mpf;
	prev_pgno = PGNO_INVALID;
	meta = NULL;
	prev = NULL;
	LOCK_INIT(metalock);
#ifdef HAVE_FTRUNCATE
	lp = NULL;
	nelem = 0;
	do_truncate = 0;
#endif

	/*
	 * Retrieve the metadata page.  If we are not keeping a sorted
	 * free list put the page at the head of the the free list.
	 * If we are keeping a sorted free list, for truncation,
	 * then figure out where this page belongs and either
	 * link it in or truncate the file as much as possible.
	 * If either the lock get or page get routines
	 * fail, then we need to put the page with which we were called
	 * back because our caller assumes we take care of it.
	 */
	hash = 0;

	pgno = PGNO_BASE_MD;
	if ((ret = __db_lget(dbc,
	    LCK_ALWAYS, pgno, DB_LOCK_WRITE, 0, &metalock)) != 0)
		goto err;

#ifdef HAVE_HASH
	if (dbp->type == DB_HASH) {
		if ((ret = __ham_return_meta(dbc,
#ifdef HAVE_FTRUNCATE
		    0,
#else
		    DB_MPOOL_DIRTY,
#endif
		&meta)) != 0)
			goto err;
		if (meta != NULL)
			hash = 1;
	}
#endif
	if (meta == NULL) {
		/* If we support truncate, we might not dirty the meta page. */
		if ((ret = __memp_fget(mpf, &pgno, dbc->thread_info, dbc->txn,
#ifdef HAVE_FTRUNCATE
		    0,
#else
		    DB_MPOOL_DIRTY,
#endif
		    &meta)) != 0)
			goto err1;
	}

	last_pgno = meta->last_pgno;
	next_pgno = meta->free;
	/*
	 * Assign lsnp here so it always initialized when
	 * HAVE_FTRUNCATE is not defined.
	 */
	lsnp = &LSN(meta);

	DB_ASSERT(dbp->env, h->pgno != next_pgno);

#ifdef HAVE_FTRUNCATE
	/*
	 * If we are maintaining a sorted free list see if we either have a
	 * new truncation point or the page goes somewhere in the middle of
	 * the list.  If it goes in the middle of the list, we will drop the
	 * meta page and get the previous page.
	 */
	COMPQUIET(position, 0);
	if ((ret = __memp_get_freelist(mpf, &nelem, &list)) != 0)
		goto err1;
	if (list == NULL)
		goto no_sort;

	if (h->pgno != last_pgno) {
		/*
		 * Put the page number in the sorted list.  Find its
		 * position and the previous page.  After logging we
		 * will extend the list, make room and insert the page in
		 * the list.
		 */
		position = 0;
		if (nelem != 0) {
			__db_freelist_pos(h->pgno, list, nelem, &position);

			DB_ASSERT(dbp->env, h->pgno != list[position]);

			/* Get the previous page if this is not the smallest. */
			if (position != 0 || h->pgno > list[0])
				prev_pgno = list[position];
		}

	} else if (nelem != 0) {
		/* Find the truncation point. */
		for (lp = &list[nelem - 1]; lp >= list; lp--)
			if (--last_pgno != *lp)
				break;
		if (lp < list || last_pgno < h->pgno - 1)
			do_truncate = 1;
		last_pgno = meta->last_pgno;
	}

no_sort:
	if (prev_pgno == PGNO_INVALID) {
#ifdef HAVE_HASH
		if (hash) {
			if ((ret =
			    __ham_return_meta(dbc, DB_MPOOL_DIRTY, &meta)) != 0)
				goto err1;
		} else
#endif
		if ((ret = __memp_dirty(mpf,
		    &meta, dbc->thread_info, dbc->txn, dbc->priority, 0)) != 0)
			goto err1;
		lsnp = &LSN(meta);
	} else {
		pgno = prev_pgno;
		if ((ret = __memp_fget(mpf, &pgno,
		    dbc->thread_info, dbc->txn, DB_MPOOL_DIRTY, &prev)) != 0)
			goto err1;
		next_pgno = NEXT_PGNO(prev);
		lsnp = &LSN(prev);
	}
#endif

	/*
	 * Log the change.
	 *	We are either logging an update to the metapage or to the
	 * previous page in the sorted list.
	 */
	if (DBC_LOGGING(dbc)) {
		memset(&ldbt, 0, sizeof(ldbt));
		ldbt.data = h;
		ldbt.size = P_OVERHEAD(dbp);
		/*
		 * If we are removing pages from the file, we need to make
		 * sure the logging happens before the truncation.  If we
		 * are truncating multiple pages we don't need to flush the
		 * log here as it will be flushed by __db_truncate_freelist.
		 */
		lflag = 0;

#ifdef HAVE_FTRUNCATE
		if (h->pgno == last_pgno && do_truncate == 0)
			lflag = DB_FLUSH;
#endif
		switch (h->type) {
		case P_HASH:
		case P_IBTREE:
		case P_IRECNO:
		case P_LBTREE:
		case P_LRECNO:
		case P_LDUP:
			if (h->entries > 0 && (h->pgno == last_pgno ||
			    !LF_ISSET(DB_LOG_NO_DATA))) {
				ldbt.size += h->entries * sizeof(db_indx_t);
				ddbt.data = (u_int8_t *)h + HOFFSET(h);
				ddbt.size = dbp->pgsize - HOFFSET(h);
				if ((ret = __db_pg_freedata_log(dbp, dbc->txn,
				     lsnp, lflag,
				     h->pgno, lsnp, pgno,
				     &ldbt, next_pgno, last_pgno, &ddbt)) != 0)
					goto err1;
				goto logged;
			}
			break;
		case P_HASHMETA:
			ldbt.size = sizeof(HMETA);
			break;
		case P_BTREEMETA:
			ldbt.size = sizeof(BTMETA);
			break;
		case P_OVERFLOW:
			ldbt.size += OV_LEN(h);
			break;
		default:
			DB_ASSERT(dbp->env, h->type != P_QAMDATA);
		}

		if ((ret = __db_pg_free_log(dbp,
		      dbc->txn, lsnp, lflag, h->pgno,
		      lsnp, pgno, &ldbt, next_pgno, last_pgno)) != 0)
			goto err1;
	} else
		LSN_NOT_LOGGED(*lsnp);

logged:
#ifdef HAVE_FTRUNCATE
	if (do_truncate) {
		start = (u_int32_t) (lp - list) + 1;
		meta->last_pgno--;
		ret = __db_truncate_freelist(
		      dbc, meta, h, list, start, nelem);
		h = NULL;
	} else if (h->pgno == last_pgno) {
		/*
		 * We are going to throw this page away, but if we are
		 * using MVCC then this version may stick around and we
		 * might have to make a copy.
		 */
		if (atomic_read(&mpf->mfp->multiversion) &&
		    (ret = __memp_dirty(mpf,
		    &h, dbc->thread_info, dbc->txn, dbc->priority, 0)) != 0)
			goto err1;
		LSN(h) = *lsnp;
		P_INIT(h, dbp->pgsize,
		    h->pgno, PGNO_INVALID, next_pgno, 0, P_INVALID);
		if ((ret = __memp_fput(mpf,
		    dbc->thread_info, h, DB_PRIORITY_VERY_LOW)) != 0)
			goto err1;
		h = NULL;
		/* Give the page back to the OS. */
		if ((ret = __memp_ftruncate(mpf, dbc->txn, dbc->thread_info,
		    last_pgno, 0)) != 0)
			goto err1;
		DB_ASSERT(dbp->env, meta->pgno == PGNO_BASE_MD);
		meta->last_pgno--;
	} else {
		if (list != NULL) {
			/* Put the page number into the list. */
			if ((ret =
			    __memp_extend_freelist(mpf, nelem + 1, &list)) != 0)
				goto err1;
			if (prev_pgno != PGNO_INVALID)
				lp = &list[position + 1];
			else
				lp = list;
			if (nelem != 0 && position != nelem)
				memmove(lp + 1, lp, (size_t)
				    ((u_int8_t*)&list[nelem] - (u_int8_t*)lp));
			*lp = h->pgno;
		}
#else
	{
#endif
		/*
		 * If we are not truncating the page then we
		 * reinitialize it and put it at the head of
		 * the free list.
		 */
		if ((ret = __memp_dirty(mpf,
		    &h, dbc->thread_info, dbc->txn, dbc->priority, 0)) != 0)
			goto err1;
		LSN(h) = *lsnp;
		P_INIT(h, dbp->pgsize,
		    h->pgno, PGNO_INVALID, next_pgno, 0, P_INVALID);
#ifdef DIAGNOSTIC
		memset((u_int8_t *) h + P_OVERHEAD(dbp),
		    CLEAR_BYTE, dbp->pgsize - P_OVERHEAD(dbp));
#endif
		if (prev_pgno == PGNO_INVALID)
			meta->free = h->pgno;
		else
			NEXT_PGNO(prev) = h->pgno;
	}

	/* Discard the metadata or previous page. */
err1:	if (hash == 0 && meta != NULL && (t_ret = __memp_fput(mpf,
	    dbc->thread_info, (PAGE *)meta, dbc->priority)) != 0 && ret == 0)
		ret = t_ret;
	if ((t_ret = __TLPUT(dbc, metalock)) != 0 && ret == 0)
		ret = t_ret;
	if (prev != (PAGE*) meta && prev != NULL && (t_ret = __memp_fput(mpf,
	    dbc->thread_info, prev, dbc->priority)) != 0 && ret == 0)
		ret = t_ret;

	/* Discard the caller's page reference. */
err:	if (h != NULL && (t_ret = __memp_fput(mpf,
	    dbc->thread_info, h, dbc->priority)) != 0 && ret == 0)
		ret = t_ret;

	PERFMON4(dbp->env, alloc, free, dbp->fname, dbp->dname, pgno, ret);
	/*
	 * !!!
	 * We have to unlock the caller's page in the caller!
	 */
	return (ret);
}

#ifdef HAVE_FTRUNCATE
/*
 * __db_freelist_pos -- find the position of a page in the freelist.
 *	The list is sorted, we do a binary search.
 *
 * PUBLIC: #ifdef HAVE_FTRUNCATE
 * PUBLIC: void __db_freelist_pos __P((db_pgno_t,
 * PUBLIC:       db_pgno_t *, u_int32_t, u_int32_t *));
 * PUBLIC: #endif
 */
void
__db_freelist_pos(pgno, list, nelem, posp)
	db_pgno_t pgno;
	db_pgno_t *list;
	u_int32_t nelem;
	u_int32_t *posp;
{
	u_int32_t base, indx, lim;

	indx = 0;
	for (base = 0, lim = nelem; lim != 0; lim >>= 1) {
		indx = base + (lim >> 1);
		if (pgno == list[indx]) {
			*posp = indx;
			return;
		}
		if (pgno > list[indx]) {
			base = indx + 1;
			--lim;
		}
	}
	if (base != 0)
		base--;
	*posp = base;
	return;
}

static int
__db_pglistcmp(a, b)
	const void *a, *b;
{
	db_pglist_t *ap, *bp;

	ap = (db_pglist_t *)a;
	bp = (db_pglist_t *)b;

	return ((ap->pgno > bp->pgno) ? 1 : (ap->pgno < bp->pgno) ? -1: 0);
}

/*
 * __db_freelist_sort -- sort a list of free pages.
 * PUBLIC: void __db_freelist_sort __P((db_pglist_t *, u_int32_t));
 */
void
__db_freelist_sort(list, nelems)
	db_pglist_t *list;
	u_int32_t nelems;
{
	qsort(list, (size_t)nelems, sizeof(db_pglist_t), __db_pglistcmp);
}

/*
 * __db_pg_truncate -- find the truncation point in a sorted freelist.
 *
 * PUBLIC: #ifdef HAVE_FTRUNCATE
 * PUBLIC: int __db_pg_truncate __P((DBC *, DB_TXN *,
 * PUBLIC:    db_pglist_t *, DB_COMPACT *, u_int32_t *,
 * PUBLIC:    db_pgno_t , db_pgno_t *, DB_LSN *, int));
 * PUBLIC: #endif
 */
int
__db_pg_truncate(dbc, txn,
    list, c_data, nelemp, free_pgno, last_pgno, lsnp, in_recovery)
	DBC *dbc;
	DB_TXN *txn;
	db_pglist_t *list;
	DB_COMPACT *c_data;
	u_int32_t *nelemp;
	db_pgno_t free_pgno, *last_pgno;
	DB_LSN *lsnp;
	int in_recovery;
{
	DB *dbp;
	DBT ddbt;
	DB_LSN null_lsn;
	DB_MPOOLFILE *mpf;
	PAGE *h;
	db_pglist_t *lp, *slp;
	db_pgno_t lpgno, pgno;
	u_int32_t elems, log_size, tpoint;
	int last, ret;

	ret = 0;
	h = NULL;

	dbp = dbc->dbp;
	mpf = dbp->mpf;
	elems = tpoint = *nelemp;

	/*
	 * Figure out what (if any) pages can be truncated immediately and
	 * record the place from which we can truncate, so we can do the
	 * memp_ftruncate below.  We also use this to avoid ever putting
	 * these pages on the freelist, which we are about to relink.
	 */
	pgno = *last_pgno;
	lp = &list[elems - 1];
	last = 1;
	while (tpoint != 0) {
		if (lp->pgno != pgno)
			break;
		pgno--;
		tpoint--;
		lp--;
	}

	lp = list;
	slp = &list[elems];
	/*
	 * Log the sorted list. We log the whole list so it can be rebuilt.
	 * Don't overflow the log file.
	 */
again:	if (DBC_LOGGING(dbc)) {
		last = 1;
		lpgno = *last_pgno;
		ddbt.size = elems * sizeof(*lp);
		ddbt.data = lp;
		log_size = ((LOG *)dbc->env->
		    lg_handle->reginfo.primary)->log_size;
		if (ddbt.size > log_size / 2) {
			elems = (log_size / 2) / sizeof(*lp);
			ddbt.size = elems * sizeof(*lp);
			last = 0;
			/*
			 * If we stopped after the truncation point
			 * then we need to truncate from here.
			 */
			if (lp + elems >= &list[tpoint])
				lpgno = lp[elems - 1].pgno;
		}
		/*
		 * If this is not the beginning of the list fetch the end
		 * of the previous segment.  This page becomes the last_free
		 * page and will link to this segment if it is not truncated.
		 */
		if (lp != list) {
			if ((ret = __memp_fget(mpf, &lp[-1].pgno,
			    dbc->thread_info, txn, 0, &h)) != 0)
				goto err;
		}

		slp = &lp[elems];

		ZERO_LSN(null_lsn);
		if ((ret = __db_pg_trunc_log(dbp, dbc->txn,
		     lsnp, last == 1 ? DB_FLUSH : 0, PGNO_BASE_MD,
		     lsnp, h != NULL ? PGNO(h) : PGNO_INVALID,
		     h != NULL ? &LSN(h) : &null_lsn,
		     free_pgno, lpgno, &ddbt)) != 0)
			goto err;
		if (h != NULL) {
			LSN(h) = *lsnp;
			if ((ret = __memp_fput(mpf,
			    dbc->thread_info, h, dbc->priority)) != 0)
				goto err;
		}
		h = NULL;
	} else if (!in_recovery)
		LSN_NOT_LOGGED(*lsnp);

	for (; lp < slp && lp < &list[tpoint]; lp++) {
		if ((ret = __memp_fget(mpf, &lp->pgno, dbc->thread_info,
		    txn, !in_recovery ? DB_MPOOL_DIRTY : 0, &h)) != 0) {
			/* Page may have been truncated later. */
			if (in_recovery && ret == DB_PAGE_NOTFOUND) {
				ret = 0;
				continue;
			}
			goto err;
		}
		if (in_recovery) {
			if (LOG_COMPARE(&LSN(h), &lp->lsn) == 0) {
				if ((ret = __memp_dirty(mpf, &h,
				    dbc->thread_info,
				    txn, dbp->priority, 0)) != 0) {
					(void)__memp_fput(mpf,
					    dbc->thread_info, h, dbp->priority);
					goto err;
				}
			} else
				goto skip;
		}

		if (lp == &list[tpoint - 1])
			NEXT_PGNO(h) = PGNO_INVALID;
		else
			NEXT_PGNO(h) = lp[1].pgno;
		DB_ASSERT(mpf->env, NEXT_PGNO(h) < *last_pgno);

		LSN(h) = *lsnp;
skip:		if ((ret = __memp_fput(mpf,
		    dbc->thread_info, h, dbp->priority)) != 0)
			goto err;
		h = NULL;
	}

	/*
	 * If we did not log everything try again.  We start from slp and
	 * try to go to the end of the list.
	 */
	if (last == 0) {
		elems = (u_int32_t)(&list[*nelemp] - slp);
		lp = slp;
		goto again;
	}

	/*
	 * Truncate the file.  Its possible that the last page is the
	 * only one that got truncated and that's done in the caller.
	 */
	if (pgno != *last_pgno) {
		if (tpoint != *nelemp &&
		    (ret = __memp_ftruncate(mpf, dbc->txn, dbc->thread_info,
		    pgno + 1, in_recovery ? MP_TRUNC_RECOVER : 0)) != 0)
			goto err;
		if (c_data)
			c_data->compact_pages_truncated += *last_pgno - pgno;
		*last_pgno = pgno;
	}
	*nelemp = tpoint;

	if (0) {
err:		if (h != NULL)
			(void)__memp_fput(mpf,
			    dbc->thread_info, h, dbc->priority);
	}
	return (ret);
}

/*
 * __db_free_truncate --
 *	  Build a sorted free list and truncate free pages at the end
 *	  of the file.
 *
 * PUBLIC: #ifdef HAVE_FTRUNCATE
 * PUBLIC: int __db_free_truncate __P((DB *, DB_THREAD_INFO *, DB_TXN *,
 * PUBLIC:    u_int32_t, DB_COMPACT *, db_pglist_t **, u_int32_t *,
 * PUBLIC:    db_pgno_t *));
 * PUBLIC: #endif
 */
int
__db_free_truncate(dbp, ip, txn, flags, c_data, listp, nelemp, last_pgnop)
	DB *dbp;
	DB_THREAD_INFO *ip;
	DB_TXN *txn;
	u_int32_t flags;
	DB_COMPACT *c_data;
	db_pglist_t **listp;
	u_int32_t *nelemp;
	db_pgno_t *last_pgnop;
{
	DBC *dbc;
	DBMETA *meta;
	DB_LOCK metalock;
	DB_MPOOLFILE *mpf;
	ENV *env;
	PAGE *h;
	db_pglist_t *list, *lp;
	db_pgno_t pgno;
	u_int32_t nelems;
	int ret, t_ret;
	size_t size;

	COMPQUIET(flags, 0);
	list = NULL;
	meta = NULL;
	env = dbp->env;
	mpf = dbp->mpf;
	h = NULL;
	nelems = 0;
	if (listp != NULL) {
		*listp = NULL;
		DB_ASSERT(env, nelemp != NULL);
		*nelemp = 0;
	}

	if ((ret = __db_cursor(dbp, ip, txn, &dbc, DB_WRITELOCK)) != 0)
		return (ret);

	pgno = PGNO_BASE_MD;
	if ((ret = __db_lget(dbc,
	    LCK_ALWAYS, pgno, DB_LOCK_WRITE, 0, &metalock)) != 0)
		goto err;
	if ((ret = __memp_fget(mpf, &pgno, dbc->thread_info, dbc->txn, 0,
	    &meta)) != 0)
		goto err;

	if (last_pgnop != NULL)
		*last_pgnop = meta->last_pgno;
	if ((pgno = meta->free) == PGNO_INVALID)
		goto done;

	size = 128;
	if ((ret = __os_malloc(env, size * sizeof(*list), &list)) != 0)
		goto err;
	lp = list;

	do {
		if (lp == &list[size]) {
			size *= 2;
			if ((ret = __os_realloc(env,
			    size * sizeof(*list), &list)) != 0)
				goto err;
			lp = &list[size / 2];
		}
		if ((ret = __memp_fget(mpf, &pgno,
		     dbc->thread_info, dbc->txn, 0, &h)) != 0)
			goto err;

		lp->pgno = pgno;
		lp->next_pgno = NEXT_PGNO(h);
		lp->lsn = LSN(h);
		pgno = NEXT_PGNO(h);
		if ((ret = __memp_fput(mpf,
		    dbc->thread_info, h, dbc->priority)) != 0)
			goto err;
		lp++;
	} while (pgno != PGNO_INVALID);
	nelems = (u_int32_t)(lp - list);

	if ((ret = __memp_dirty(mpf,
	    &meta, dbc->thread_info, dbc->txn, dbc->priority, 0)) != 0)
		goto err;

	/* Sort the list */
	__db_freelist_sort(list, nelems);

	if ((ret = __db_pg_truncate(dbc, txn, list, c_data,
	    &nelems, meta->free, &meta->last_pgno, &LSN(meta), 0)) != 0)
		goto err;

	if (nelems == 0)
		meta->free = PGNO_INVALID;
	else
		meta->free = list[0].pgno;

done:	if (last_pgnop != NULL)
		*last_pgnop = meta->last_pgno;

	/*
	 * Set the truncation point which determines which pages may be
	 * relocated. Pages above are candidates to be swapped with a lower one
	 * from the freelist by __db_exchange_page(); pages before the truncate
	 * point are not relocated.
	 * The truncation point starts as N pages less than the last_pgno, where
	 * N is the size of the free list. This is reduced by 1/4 in the hope
	 * that partially full pages will be coalesced together, creating
	 * additional free pages during the compact.
	 */
	if (c_data) {
		c_data->compact_truncate = (u_int32_t)meta->last_pgno - nelems;
		if (c_data->compact_truncate > nelems >> 2)
			c_data->compact_truncate -= nelems >> 2;
	}

	if (nelems != 0 && listp != NULL) {
		*listp = list;
		*nelemp = nelems;
		list = NULL;
	}

err:	if (list != NULL)
		__os_free(env, list);
	if (meta != NULL && (t_ret = __memp_fput(mpf,
	     dbc->thread_info, (PAGE *)meta, dbc->priority)) != 0 && ret == 0)
		ret = t_ret;
	if ((t_ret = __TLPUT(dbc, metalock)) != 0 && ret == 0)
		ret = t_ret;
	if ((t_ret = __dbc_close(dbc)) != 0 && ret == 0)
		ret = t_ret;
	return (ret);
}

static int
__db_truncate_freelist(dbc, meta, h, list, start, nelem)
	DBC *dbc;
	DBMETA *meta;
	PAGE *h;
	db_pgno_t *list;
	u_int32_t start, nelem;
{
	DB *dbp;
	DBT ddbt;
	DB_LSN null_lsn;
	DB_MPOOLFILE *mpf;
	PAGE *last_free, *pg;
	db_pgno_t *lp, free_pgno, lpgno;
	db_pglist_t *plist, *pp, *spp;
	u_int32_t elem, log_size;
	int last, ret;

	dbp = dbc->dbp;
	mpf = dbp->mpf;
	plist = NULL;
	last_free = NULL;
	pg = NULL;

	if (start != 0 &&
	    (ret = __memp_fget(mpf, &list[start - 1],
	    dbc->thread_info, dbc->txn, DB_MPOOL_DIRTY, &last_free)) != 0)
		goto err;

	if (DBC_LOGGING(dbc)) {
		if ((ret = __os_malloc(dbp->env,
		     (nelem - start) * sizeof(*pp), &plist)) != 0)
			goto err;

		pp = plist;
		for (lp = &list[start]; lp < &list[nelem]; lp++) {
			pp->pgno = *lp;
			if ((ret = __memp_fget(mpf, lp,
			     dbc->thread_info, dbc->txn, 0, &pg)) != 0)
				goto err;
			pp->lsn = LSN(pg);
			pp->next_pgno = NEXT_PGNO(pg);
			if ((ret = __memp_fput(mpf,
			    dbc->thread_info, pg, DB_PRIORITY_VERY_LOW)) != 0)
				goto err;
			pg = NULL;
			pp++;
		}
		ZERO_LSN(null_lsn);
		pp = plist;
		elem = nelem - start;
		log_size = ((LOG *)dbc->env->
		    lg_handle->reginfo.primary)->log_size;
again:		ddbt.data = spp = pp;
		free_pgno = pp->pgno;
		lpgno = meta->last_pgno;
		ddbt.size = elem * sizeof(*pp);
		if (ddbt.size > log_size / 2) {
			elem = (log_size / 2) / (u_int32_t)sizeof(*pp);
			ddbt.size = elem * sizeof(*pp);
			pp += elem;
			elem = (nelem - start) - (u_int32_t)(pp - plist);
			lpgno = pp[-1].pgno;
			last = 0;
		} else
			last = 1;
		/*
		 * Get the page which will link to this section if we abort.
		 * If this is the first segment then its last_free.
		 */
		if (spp == plist)
			pg = last_free;
		else if ((ret = __memp_fget(mpf, &spp[-1].pgno,
		     dbc->thread_info, dbc->txn, DB_MPOOL_DIRTY, &pg)) != 0)
			goto err;

		if ((ret = __db_pg_trunc_log(dbp, dbc->txn,
		     &LSN(meta), last == 1 ? DB_FLUSH : 0,
		     PGNO(meta), &LSN(meta),
		     pg != NULL ? PGNO(pg) : PGNO_INVALID,
		     pg != NULL ? &LSN(pg) : &null_lsn,
		     free_pgno, lpgno, &ddbt)) != 0)
			goto err;
		if (pg != NULL) {
			LSN(pg) = LSN(meta);
			if (pg != last_free && (ret = __memp_fput(mpf,
			    dbc->thread_info, pg, DB_PRIORITY_VERY_LOW)) != 0)
				goto err;
			pg = NULL;
		}
		if (last == 0)
			goto again;
	} else
		LSN_NOT_LOGGED(LSN(meta));

	if ((ret = __memp_fput(mpf,
	    dbc->thread_info, h, DB_PRIORITY_VERY_LOW)) != 0)
		goto err;
	h = NULL;
	if ((ret = __memp_ftruncate(mpf, dbc->txn, dbc->thread_info,
	    list[start], 0)) != 0)
		goto err;
	meta->last_pgno = list[start] - 1;

	if (start == 0)
		meta->free = PGNO_INVALID;
	else {
		NEXT_PGNO(last_free) = PGNO_INVALID;
		if ((ret = __memp_fput(mpf,
		    dbc->thread_info, last_free, dbc->priority)) != 0)
			goto err;
		last_free = NULL;
	}

	/* Shrink the number of elements in the list. */
	ret = __memp_extend_freelist(mpf, start, &list);

err:	if (plist != NULL)
		__os_free(dbp->env, plist);

	/* We need to put the page on error. */
	if (h != NULL)
		(void)__memp_fput(mpf, dbc->thread_info, h, dbc->priority);
	if (pg != NULL && pg != last_free)
		(void)__memp_fput(mpf, dbc->thread_info, pg, dbc->priority);
	if (last_free != NULL)
		(void)__memp_fput(mpf,
		    dbc->thread_info, last_free, dbc->priority);

	return (ret);
}
#endif

#ifdef DEBUG
/*
 * __db_lprint --
 *	Print out the list of locks currently held by a cursor.
 *
 * PUBLIC: int __db_lprint __P((DBC *));
 */
int
__db_lprint(dbc)
	DBC *dbc;
{
	DB *dbp;
	DB_LOCKREQ req;
	ENV *env;

	dbp = dbc->dbp;
	env = dbp->env;

	if (LOCKING_ON(env)) {
		req.op = DB_LOCK_DUMP;
		(void)__lock_vec(env, dbc->locker, 0, &req, 1, NULL);
	}
	return (0);
}
#endif

/*
 * __db_lget --
 *	The standard lock get call.
 *
 * PUBLIC: int __db_lget __P((DBC *,
 * PUBLIC:     int, db_pgno_t, db_lockmode_t, u_int32_t, DB_LOCK *));
 */
int
__db_lget(dbc, action, pgno, mode, lkflags, lockp)
	DBC *dbc;
	int action;
	db_pgno_t pgno;
	db_lockmode_t mode;
	u_int32_t lkflags;
	DB_LOCK *lockp;
{
	DB *dbp;
	DB_LOCKREQ couple[3], *reqp;
	DB_TXN *txn;
	ENV *env;
	int has_timeout, i, ret;

	dbp = dbc->dbp;
	env = dbp->env;
	txn = dbc->txn;

	/*
	 * We do not always check if we're configured for locking before
	 * calling __db_lget to acquire the lock.
	 */
	if (CDB_LOCKING(env) || !LOCKING_ON(env) ||
	    (MULTIVERSION(dbp) && mode == DB_LOCK_READ &&
	    dbc->txn != NULL && F_ISSET(dbc->txn, TXN_SNAPSHOT)) ||
	    F_ISSET(dbc, DBC_DONTLOCK) || (F_ISSET(dbc, DBC_RECOVER) &&
	    (action != LCK_ROLLBACK || IS_REP_CLIENT(env))) ||
	    (action != LCK_ALWAYS && F_ISSET(dbc, DBC_OPD))) {
		LOCK_INIT(*lockp);
		return (0);
	}

	/*
	 * If the transaction enclosing this cursor has DB_LOCK_NOWAIT set,
	 * pass that along to the lock call.
	 */
	if (DB_NONBLOCK(dbc))
		lkflags |= DB_LOCK_NOWAIT;

	/*
	 * If we're trying to run in exclusive mode, attempt to get an
	 * exclusive database lock.  If it is not available then wait
	 * for the lock on the database and clear the exclusive bit.
	 *
	 * If we get an exclusive lock on the database, mark the cursor
	 * with DBC_DONTLOCK to avoid any further locking.
	 */
	if (F_ISSET(dbp->mpf->mfp, MP_DATABASE_LOCKING)) {
		dbc->lock.type = DB_DATABASE_LOCK;
		dbc->lock.pgno = PGNO_BASE_MD;
		if ((ret = __lock_get(env, dbc->locker, DB_LOCK_NOWAIT,
		    &dbc->lock_dbt, F_ISSET(dbp, DB_AM_RDONLY) ?
		    DB_LOCK_READ : DB_LOCK_WRITE, lockp)) == 0) {
			if (F_ISSET(dbp->mpf->mfp, MP_DATABASE_LOCKING)) {
				F_SET(dbc, DBC_DONTLOCK);
				if (!IS_REAL_TXN(txn))
					dbc->mylock = *lockp;
				LOCK_INIT(*lockp);
				return (0);
			}
		} else if (ret == DB_LOCK_NOTGRANTED &&
		    (lkflags & DB_LOCK_NOWAIT) == 0) {
			if ((ret = __lock_get(env, dbc->locker, 0,
			    &dbc->lock_dbt, DB_LOCK_WRITE, lockp)) != 0)
				return (ret);
			F_CLR(dbp->mpf->mfp, MP_DATABASE_LOCKING);
			if ((ret = __lock_put(env, lockp)) != 0)
				return (ret);
			LOCK_INIT(*lockp);
		} else if (ret != 0)
			return (ret);
	}

	dbc->lock.pgno = pgno;
	if (lkflags & DB_LOCK_RECORD)
		dbc->lock.type = DB_RECORD_LOCK;
	else
		dbc->lock.type = DB_PAGE_LOCK;
	lkflags &= ~DB_LOCK_RECORD;

	if (F_ISSET(dbc, DBC_READ_UNCOMMITTED) && mode == DB_LOCK_READ)
		mode = DB_LOCK_READ_UNCOMMITTED;

	has_timeout = F_ISSET(dbc, DBC_RECOVER) ||
	    (txn != NULL && F_ISSET(txn, TXN_LOCKTIMEOUT));

	/*
	 * Transactional locking.
	 * Hold on to the previous read lock only if we are in full isolation.
	 * COUPLE_ALWAYS indicates we are holding an interior node which need
	 *	not be isolated.
	 * Downgrade write locks if we are supporting dirty readers and the
	 * update did not have an error.
	 */
	if ((action != LCK_COUPLE && action != LCK_COUPLE_ALWAYS) ||
	    !LOCK_ISSET(*lockp))
		action = 0;
	else if (dbc->txn == NULL || action == LCK_COUPLE_ALWAYS)
		action = LCK_COUPLE;
	else if (F_ISSET(dbc, DBC_READ_COMMITTED | DBC_WAS_READ_COMMITTED) &&
	    lockp->mode == DB_LOCK_READ)
		action = LCK_COUPLE;
	else if (lockp->mode == DB_LOCK_READ_UNCOMMITTED)
		action = LCK_COUPLE;
	else if (F_ISSET(dbc->dbp, DB_AM_READ_UNCOMMITTED) &&
	     !F_ISSET(dbc, DBC_ERROR) && lockp->mode == DB_LOCK_WRITE)
		action = LCK_DOWNGRADE;
	else
		action = 0;

	i = 0;
	switch (action) {
	default:
		if (has_timeout)
			goto do_couple;
		ret = __lock_get(env,
		    dbc->locker, lkflags, &dbc->lock_dbt, mode, lockp);
		break;

	case LCK_DOWNGRADE:
		couple[0].op = DB_LOCK_GET;
		couple[0].obj = NULL;
		couple[0].lock = *lockp;
		couple[0].mode = DB_LOCK_WWRITE;
		UMRW_SET(couple[0].timeout);
		i++;
		/* FALLTHROUGH */
	case LCK_COUPLE:
do_couple:	couple[i].op = has_timeout? DB_LOCK_GET_TIMEOUT : DB_LOCK_GET;
		couple[i].obj = &dbc->lock_dbt;
		couple[i].mode = mode;
		UMRW_SET(couple[i].timeout);
		i++;
		if (has_timeout)
			couple[0].timeout =
			     F_ISSET(dbc, DBC_RECOVER) ? 0 : txn->lock_timeout;
		if (action == LCK_COUPLE || action == LCK_DOWNGRADE) {
			couple[i].op = DB_LOCK_PUT;
			couple[i].lock = *lockp;
			i++;
		}

		ret = __lock_vec(env,
		    dbc->locker, lkflags, couple, i, &reqp);
		if (ret == 0 || reqp == &couple[i - 1])
			*lockp = i == 1 ? couple[0].lock : couple[i - 2].lock;
		break;
	}

	if (txn != NULL && ret == DB_LOCK_DEADLOCK)
		F_SET(txn, TXN_DEADLOCK);
	return ((ret == DB_LOCK_NOTGRANTED && !F_ISSET(env->dbenv,
		 DB_ENV_TIME_NOTGRANTED)) ? DB_LOCK_DEADLOCK : ret);
}

#ifdef DIAGNOSTIC
/*
 * __db_haslock --
 *	Determine if this locker holds a particular lock.
 *	Returns 0 if lock is held, non-zero otherwise.
 *
 * PUBLIC: #ifdef DIAGNOSTIC
 * PUBLIC: int __db_haslock __P((ENV *, DB_LOCKER *,
 * PUBLIC:     DB_MPOOLFILE *, db_pgno_t, db_lockmode_t, u_int32_t));
 * PUBLIC: #endif
 */
int
__db_haslock(env, locker, dbmfp, pgno, mode, type)
	ENV *env;
	DB_LOCKER *locker;
	DB_MPOOLFILE *dbmfp;
	db_pgno_t pgno;
	db_lockmode_t mode;
	u_int32_t type;
{
	DBT lkdata;
	DB_LOCK lock;
	DB_LOCK_ILOCK ilock;

	memset(&lkdata, 0, sizeof(lkdata));
	lkdata.data = &ilock;
	lkdata.size = sizeof(ilock);

	memcpy(ilock.fileid, dbmfp->fileid, DB_FILE_ID_LEN);
	ilock.pgno = pgno;
	ilock.type = type;

	return (__lock_get(env, locker, DB_LOCK_CHECK, &lkdata, mode, &lock));
}
/*
 * __db_has_pagelock --
 *	Determine if this locker holds a particular page lock, and return an
 *	error if it is missing a page lock that it should have.
 *	Otherwise (TDS with the page locked, or DS or CDS) return 0.
 *
 * PUBLIC: #ifdef DIAGNOSTIC
 * PUBLIC: int __db_has_pagelock __P((ENV *, DB_LOCKER *,
 * PUBLIC:     DB_MPOOLFILE *, PAGE *, db_lockmode_t));
 * PUBLIC: #endif
 */
int
__db_has_pagelock(env, locker, dbmfp, pagep, mode)
	ENV *env;
	DB_LOCKER *locker;
	DB_MPOOLFILE *dbmfp;
	PAGE *pagep;
	db_lockmode_t mode;
{
	int ret;

	if (!FLD_ISSET(env->open_flags, DB_INIT_TXN))
		return (0);

	switch (pagep->type) {
	case P_OVERFLOW:
	case P_INVALID:
	case P_QAMDATA:
	case P_QAMMETA:
	case P_IHEAP:
		return (0);
	case P_HASH:
		if (PREV_PGNO(pagep) != PGNO_INVALID)
			return (0);
		break;
	default:
		break;
	}
	if ((ret = __db_haslock(env,
	    locker, dbmfp, pagep->pgno, mode, DB_PAGE_LOCK)) != 0)
		ret = __db_haslock(env,
		    locker, dbmfp, PGNO_BASE_MD, mode, DB_DATABASE_LOCK);
	return (ret);
}
#endif

/*
 * __db_lput --
 *	The standard lock put call.
 *
 * PUBLIC: int __db_lput __P((DBC *, DB_LOCK *));
 */
int
__db_lput(dbc, lockp)
	DBC *dbc;
	DB_LOCK *lockp;
{
	DB_LOCKREQ couple[2], *reqp;
	ENV *env;
	int action, ret;

	/*
	 * Transactional locking.
	 * Hold on to the read locks only if we are in full isolation.
	 * Downgrade write locks if we are supporting dirty readers unless
	 * there was an error.
	 */
	if (F_ISSET(dbc->dbp, DB_AM_READ_UNCOMMITTED) &&
	    !F_ISSET(dbc, DBC_ERROR) && lockp->mode == DB_LOCK_WRITE)
		action = LCK_DOWNGRADE;
	else if (dbc->txn == NULL)
		action = LCK_COUPLE;
	else if (F_ISSET(dbc, DBC_READ_COMMITTED | DBC_WAS_READ_COMMITTED) &&
	    lockp->mode == DB_LOCK_READ)
		action = LCK_COUPLE;
	else if (lockp->mode == DB_LOCK_READ_UNCOMMITTED)
		action = LCK_COUPLE;
	else
		action = 0;

	env = dbc->env;
	switch (action) {
	case LCK_COUPLE:
		ret = __lock_put(env, lockp);
		break;
	case LCK_DOWNGRADE:
		couple[0].op = DB_LOCK_GET;
		couple[0].obj = NULL;
		couple[0].mode = DB_LOCK_WWRITE;
		couple[0].lock = *lockp;
		UMRW_SET(couple[0].timeout);
		couple[1].op = DB_LOCK_PUT;
		couple[1].lock = *lockp;
		ret = __lock_vec(env, dbc->locker, 0, couple, 2, &reqp);
		if (ret == 0 || reqp == &couple[1])
			*lockp = couple[0].lock;
		break;
	default:
		ret = 0;
		break;
	}

	return (ret);
}