db_meta.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2005
 *      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. 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: db_meta.c,v 12.22 2005/10/27 01:46:34 bostic Exp $
 */

#include "db_config.h"

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <stdlib.h>
#include <string.h>
#endif

#include "db_int.h"
#include "dbinc/db_page.h"
#include "dbinc/db_shash.h"
#include "dbinc/lock.h"
#include "dbinc/mp.h"
#include "dbinc/db_am.h"

static void __db_init_meta __P((DB *, void *, db_pgno_t, u_int32_t));
#ifdef HAVE_FTRUNCATE
static void __db_freelist_sort __P((struct pglist *, u_int32_t));
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;
{
        DB_LSN save_lsn;
        DBMETA *meta;

        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, PAGE **));
 */
int
__db_new(dbc, type, pagepp)
        DBC *dbc;
        u_int32_t type;
        PAGE **pagepp;
{
        DBMETA *meta;
        DB *dbp;
        DB_LOCK metalock;
        DB_LSN lsn;
        DB_MPOOLFILE *mpf;
        PAGE *h;
        db_pgno_t last, *list, pgno, newnext;
        u_int32_t meta_flags;
        int extend, ret, t_ret;

        meta = NULL;
        meta_flags = 0;
        dbp = dbc->dbp;
        mpf = dbp->mpf;
        h = NULL;
        newnext = PGNO_INVALID;

        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, 0, &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;
                if ((ret = __memp_fget(mpf, &pgno, 0, &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;
        }

        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_flags = DB_MPOOL_DIRTY;
        meta->free = newnext;

        if (extend == 1) {
                if ((ret = __memp_fget(mpf, &pgno, DB_MPOOL_NEW, &h)) != 0)
                        goto err;
                DB_ASSERT(last == pgno);
                meta->last_pgno = pgno;
                ZERO_LSN(h->lsn);
                h->pgno = pgno;
        }
        LSN(h) = LSN(meta);

        DB_ASSERT(TYPE(h) == P_INVALID);

        if (TYPE(h) != P_INVALID)
                return (__db_panic(dbp->dbenv, EINVAL));

        ret = __memp_fput(mpf, (PAGE *)meta, DB_MPOOL_DIRTY);
        meta = NULL;
        if ((t_ret = __TLPUT(dbc, metalock)) != 0 && ret == 0)
                ret = t_ret;
        if (ret != 0)
                goto err;

        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(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 dirty reads are enabled and we are in a transaction, we could
         * abort this allocation after the page(s) pointing to this
         * one have their locks downgraded.  This would permit dirty readers
         * to access this page which is ok, but they must be off the
         * page when we abort.  We never lock overflow pages or off page
         * duplicate trees.
         */
        if (type != P_OVERFLOW && !F_ISSET(dbc, DBC_OPD) &&
             F_ISSET(dbc->dbp, DB_AM_READ_UNCOMMITTED) && dbc->txn != NULL) {
                if ((ret = __db_lget(dbc, 0,
                    h->pgno, DB_LOCK_WWRITE, 0, &metalock)) != 0)
                        goto err;
        }

        *pagepp = h;
        return (0);

err:    if (h != NULL)
                (void)__memp_fput(mpf, h, 0);
        if (meta != NULL)
                (void)__memp_fput(mpf, meta, meta_flags);
        (void)__TLPUT(dbc, metalock);
        return (ret);
}

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

        dbp = dbc->dbp;
        mpf = dbp->mpf;
        prev_pgno = PGNO_INVALID;
        nelem = 0;
        meta = NULL;
        do_truncate = 0;
        lp = NULL;

        /*
         * 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.
         */
        dirty_flag = 0;
        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, 0, &meta)) != 0)
                goto err1;

        last_pgno = meta->last_pgno;
        next_pgno = meta->free;

        DB_ASSERT(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.
         */
        if ((ret = __memp_get_freelist(mpf, &nelem, &list)) != 0)
                goto err;
        if (list == NULL)
                goto no_sort;

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

                        DB_ASSERT(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];
                }

                /* Put the page number into the list. */
                if ((ret = __memp_extend_freelist(mpf, nelem + 1, &list)) != 0)
                        return (ret);
                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 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) {
                if ((ret = __memp_fput(mpf, meta, 0)) != 0)
                        goto err1;
                meta = NULL;
                pgno = prev_pgno;
                if ((ret = __memp_fget(mpf, &pgno, 0, &meta)) != 0)
                        goto err1;
                next_pgno = NEXT_PGNO(meta);
        }
#endif

        /* Log the change. */
        if (DBC_LOGGING(dbc)) {
                memset(&ldbt, 0, sizeof(ldbt));
                ldbt.data = h;
                ldbt.size = P_OVERHEAD(dbp);
                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) {
                                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,
                                     &LSN(meta), 0, h->pgno, &LSN(meta), 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(h->type != P_QAMDATA);
                }

                /*
                 * If we are truncating 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 (do_truncate == 0 && h->pgno == last_pgno)
                        lflag = DB_FLUSH;
#endif
                if ((ret = __db_pg_free_log(dbp,
                      dbc->txn, &LSN(meta), lflag, h->pgno,
                      &LSN(meta), pgno, &ldbt, next_pgno, last_pgno)) != 0)
                        goto err1;
        } else
                LSN_NOT_LOGGED(LSN(meta));
logged: LSN(h) = LSN(meta);

#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) {
                if ((ret = __memp_fput(mpf, h, DB_MPOOL_DISCARD)) != 0)
                        goto err;
                /* Give the page back to the OS. */
                if ((ret = __memp_ftruncate(mpf, last_pgno, 0)) != 0)
                        goto err;
                DB_ASSERT(meta->pgno == PGNO_BASE_MD);
                meta->last_pgno--;
                h = NULL;
        } else
#endif

        {
                /*
                 * If we are not truncating the page then we
                 * reinitialize it and put it at the head of
                 * the free list.
                 */
                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(meta) = h->pgno;
        }

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

        /* Discard the caller's page reference. */
        dirty_flag = DB_MPOOL_DIRTY;
err:    if (h != NULL &&
            (t_ret = __memp_fput(mpf, h, dirty_flag)) != 0 && ret == 0)
                ret = t_ret;

        /*
         * XXX
         * 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;
{
        struct pglist *ap, *bp;

        ap = (struct pglist *)a;
        bp = (struct pglist *)b;

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

/*
 * __db_freelist_sort -- sort a list of free pages.
 */
static void
__db_freelist_sort(list, nelems)
        struct pglist *list;
        u_int32_t nelems;
{
        qsort(list, (size_t)nelems, sizeof(struct pglist), __db_pglistcmp);
}

/*
 * __db_pg_truncate -- sort the freelist and find the truncation point.
 *
 * PUBLIC: #ifdef HAVE_FTRUNCATE
 * PUBLIC: int __db_pg_truncate __P((DB_MPOOLFILE *, struct pglist *list,
 * PUBLIC:    DB_COMPACT *, u_int32_t *, db_pgno_t *, DB_LSN *, int));
 * PUBLIC: #endif
 */
int
__db_pg_truncate(mpf, list, c_data, nelemp, last_pgno, lsnp, in_recovery)
        DB_MPOOLFILE *mpf;
        struct pglist *list;
        DB_COMPACT *c_data;
        u_int32_t *nelemp;
        db_pgno_t *last_pgno;
        DB_LSN *lsnp;
        int in_recovery;
{
        PAGE *h;
        struct pglist *lp;
        db_pgno_t pgno;
        u_int32_t nelems;
        int modified, ret;

        ret = 0;

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

        /* Find the truncation point. */
        pgno = *last_pgno;
        lp = &list[nelems - 1];
        while (nelems != 0) {
                if (lp->pgno != pgno)
                        break;
                pgno--;
                nelems--;
                lp--;
        }

        /*
         * 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.
         */
        for (lp = list; lp < &list[nelems]; lp++) {
                if ((ret = __memp_fget(mpf, &lp->pgno, 0, &h)) != 0) {
                        /* Page may have been truncated later. */
                        if (in_recovery && ret == DB_PAGE_NOTFOUND) {
                                ret = 0;
                                continue;
                        }
                        goto err;
                }
                modified = 0;
                if (!in_recovery || log_compare(&LSN(h), &lp->lsn) == 0) {
                        if (lp == &list[nelems - 1])
                                NEXT_PGNO(h) = PGNO_INVALID;
                        else
                                NEXT_PGNO(h) = lp[1].pgno;
                        DB_ASSERT(NEXT_PGNO(h) < *last_pgno);

                        LSN(h) = *lsnp;
                        modified = 1;
                }
                if ((ret = __memp_fput(mpf, h,
                    modified ? DB_MPOOL_DIRTY : 0)) != 0)
                        goto err;
        }

        if (pgno != *last_pgno) {
                if ((ret = __memp_ftruncate(mpf,
                    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 = nelems;

err:    return (ret);
}

/*
 * __db_free_truncate --
 *      Truncate free pages at the end of the file.
 *
 * PUBLIC: #ifdef HAVE_FTRUNCATE
 * PUBLIC: int __db_free_truncate __P((DB *, DB_TXN *, u_int32_t,
 * PUBLIC:    DB_COMPACT *, struct pglist **, u_int32_t *, db_pgno_t *));
 * PUBLIC: #endif
 */
int
__db_free_truncate(dbp, txn, flags, c_data, listp, nelemp, last_pgnop)
        DB *dbp;
        DB_TXN *txn;
        u_int32_t flags;
        DB_COMPACT *c_data;
        struct pglist **listp;
        u_int32_t *nelemp;
        db_pgno_t *last_pgnop;
{
        DBC *dbc;
        DB_ENV *dbenv;
        DBMETA *meta;
        DBT ddbt;
        DB_LOCK metalock;
        DB_LSN null_lsn;
        DB_MPOOLFILE *mpf;
        PAGE *h;
        db_pgno_t pgno;
        u_int32_t nelems;
        struct pglist *list, *lp;
        int ret, t_ret;
        size_t size;

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

        if ((ret = __db_cursor(dbp, 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, 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(dbenv, size * sizeof(*list), &list)) != 0)
                goto err;
        lp = list;

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

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

        /* Log the current state of the free list */
        if (DBC_LOGGING(dbc)) {
                ddbt.data = list;
                ddbt.size = nelems * sizeof(*lp);
                ZERO_LSN(null_lsn);
                if ((ret = __db_pg_sort_log(dbp,
                     dbc->txn, &LSN(meta), DB_FLUSH, PGNO_BASE_MD, &LSN(meta),
                     PGNO_INVALID, &null_lsn, meta->last_pgno, &ddbt)) != 0)
                        goto err;
        } else
                LSN_NOT_LOGGED(LSN(meta));

        if ((ret = __db_pg_truncate(mpf, list, c_data,
            &nelems, &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;

        /*
         * The truncate point is the number of pages in the free
         * list back from the last page.  The number of pages
         * in the free list are the number that we can swap in.
         */
        if (c_data)
                c_data->compact_truncate = (u_int32_t)meta->last_pgno - nelems;

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

err:    if (list != NULL)
                __os_free(dbenv, list);
        if (meta != NULL && (t_ret =
             __memp_fput(mpf, (PAGE *)meta, DB_MPOOL_DIRTY)) != 0 && ret == 0)
                ret = t_ret;
        if ((t_ret = __TLPUT(dbc, metalock)) != 0 && ret == 0)
                ret = t_ret;
        if ((t_ret = __db_c_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;
        DB_LSN null_lsn;
        DB_MPOOLFILE *mpf;
        DBT ddbt;
        PAGE *last_free, *pg;
        db_pgno_t *lp;
        struct pglist *plist, *pp;
        int ret;

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

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

        if (DBC_LOGGING(dbc)) {
                if ((ret = __os_malloc(dbp->dbenv,
                     (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, 0, &pg)) != 0)
                                goto err;
                        pp->lsn = LSN(pg);
                        if ((ret = __memp_fput(mpf, pg, DB_MPOOL_DISCARD)) != 0)
                                goto err;
                        pp++;
                }
                ddbt.data = plist;
                ddbt.size = (nelem - start) * sizeof(*pp);
                ZERO_LSN(null_lsn);
                if (last_free != NULL) {
                        if ((ret = __db_pg_sort_log(dbp, dbc->txn, &LSN(meta),
                             DB_FLUSH, PGNO(meta), &LSN(meta), PGNO(last_free),
                             &LSN(last_free), meta->last_pgno, &ddbt)) != 0)
                                goto err;
                } else if ((ret = __db_pg_sort_log(dbp, dbc->txn,
                     &LSN(meta), DB_FLUSH, PGNO(meta), &LSN(meta),
                     PGNO_INVALID, &null_lsn, meta->last_pgno, &ddbt)) != 0)
                        goto err;
        } else
                LSN_NOT_LOGGED(LSN(meta));
        if (last_free != NULL)
                LSN(last_free) = LSN(meta);

        if ((ret = __memp_fput(mpf, h, DB_MPOOL_DISCARD)) != 0)
                goto err;
        h = NULL;
        if ((ret = __memp_ftruncate(mpf, 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, last_free, DB_MPOOL_DIRTY)) != 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->dbenv, plist);

        /* We need to put the page on error. */
        if (h != NULL)
                (void)__memp_fput(mpf, h, 0);
        if (last_free != NULL)
                (void)__memp_fput(mpf, last_free, 0);

        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_ENV *dbenv;
        DB *dbp;
        DB_LOCKREQ req;

        dbp = dbc->dbp;
        dbenv = dbp->dbenv;

        if (LOCKING_ON(dbenv)) {
                req.op = DB_LOCK_DUMP;
                (void)__lock_vec(dbenv, 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_ENV *dbenv;
        DB_LOCKREQ couple[3], *reqp;
        DB_TXN *txn;
        int has_timeout, i, ret;

        dbp = dbc->dbp;
        dbenv = dbp->dbenv;
        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(dbenv) ||
            !LOCKING_ON(dbenv) || F_ISSET(dbc, DBC_COMPENSATE) ||
            (F_ISSET(dbc, DBC_RECOVER) &&
            (action != LCK_ROLLBACK || IS_REP_CLIENT(dbenv))) ||
            (action != LCK_ALWAYS && F_ISSET(dbc, DBC_OPD))) {
                LOCK_INIT(*lockp);
                return (0);
        }

        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 (action == LCK_ROLLBACK)
                lkflags |= DB_LOCK_ABORT;

        /*
         * 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 (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.
         */
        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) && lockp->mode == DB_LOCK_READ)
                action = LCK_COUPLE;
        else if (F_ISSET(dbc,
            DBC_READ_UNCOMMITTED) && lockp->mode == DB_LOCK_READ_UNCOMMITTED)
                action = LCK_COUPLE;
        else if (F_ISSET(dbc->dbp,
            DB_AM_READ_UNCOMMITTED) && lockp->mode == DB_LOCK_WRITE)
                action = LCK_DOWNGRADE;
        else
                action = 0;

        i = 0;
        switch (action) {
        default:
                if (has_timeout)
                        goto couple;
                ret = __lock_get(dbenv,
                    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:
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(dbenv,
                    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(dbenv, DB_ENV_TIME_NOTGRANTED)) ? DB_LOCK_DEADLOCK : ret);
}

/*
 * __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_ENV *dbenv;
        DB_LOCKREQ couple[2], *reqp;
        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.
         */
        if (F_ISSET(dbc->dbp,
            DB_AM_READ_UNCOMMITTED) && lockp->mode == DB_LOCK_WRITE)
                action = LCK_DOWNGRADE;
        else if (dbc->txn == NULL)
                action = LCK_COUPLE;
        else if (F_ISSET(dbc,
            DBC_READ_COMMITTED) && lockp->mode == DB_LOCK_READ)
                action = LCK_COUPLE;
        else if (F_ISSET(dbc,
            DBC_READ_UNCOMMITTED) && lockp->mode == DB_LOCK_READ_UNCOMMITTED)
                action = LCK_COUPLE;
        else
                action = 0;

        dbenv = dbc->dbp->dbenv;
        switch (action) {
        case LCK_COUPLE:
                ret = __lock_put(dbenv, 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(dbenv, dbc->locker, 0, couple, 2, &reqp);
                if (ret == 0 || reqp == &couple[1])
                        *lockp = couple[0].lock;
                break;
        default:
                ret = 0;
                break;
        }

        return (ret);
}

---