bt_put.c

Go to the documentation of this file.

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2002
 *      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.
 */

#include "db_config.h"

#ifndef lint
static const char revid[] = "$Id: bt_put.c,v 11.69 2002/08/06 06:11:12 bostic Exp $";
#endif /* not lint */

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

#include <string.h>
#endif

#include "db_int.h"
#include "dbinc/db_page.h"
#include "dbinc/btree.h"

static int __bam_build
               __P((DBC *, u_int32_t, DBT *, PAGE *, u_int32_t, u_int32_t));
static int __bam_dup_convert __P((DBC *, PAGE *, u_int32_t));
static int __bam_ovput
               __P((DBC *, u_int32_t, db_pgno_t, PAGE *, u_int32_t, DBT *));
static u_int32_t
           __bam_partsize __P((DB *, u_int32_t, DBT *, PAGE *, u_int32_t));

/*
 * __bam_iitem --
 *      Insert an item into the tree.
 *
 * PUBLIC: int __bam_iitem __P((DBC *, DBT *, DBT *, u_int32_t, u_int32_t));
 */
int
__bam_iitem(dbc, key, data, op, flags)
        DBC *dbc;
        DBT *key, *data;
        u_int32_t op, flags;
{
        BKEYDATA *bk, bk_tmp;
        BTREE *t;
        BTREE_CURSOR *cp;
        DB *dbp;
        DBT bk_hdr, tdbt;
        DB_MPOOLFILE *mpf;
        PAGE *h;
        db_indx_t indx;
        u_int32_t data_size, have_bytes, need_bytes, needed;
        int cmp, bigkey, bigdata, dupadjust, padrec, replace, ret, was_deleted;

        COMPQUIET(bk, NULL);

        dbp = dbc->dbp;
        mpf = dbp->mpf;
        cp = (BTREE_CURSOR *)dbc->internal;
        t = dbp->bt_internal;
        h = cp->page;
        indx = cp->indx;
        dupadjust = replace = was_deleted = 0;

        /*
         * Fixed-length records with partial puts: it's an error to specify
         * anything other simple overwrite.
         */
        if (F_ISSET(dbp, DB_AM_FIXEDLEN) &&
            F_ISSET(data, DB_DBT_PARTIAL) && data->dlen != data->size) {
                data_size = data->size;
                goto len_err;
        }

        /*
         * Figure out how much space the data will take, including if it's a
         * partial record.
         *
         * Fixed-length records: it's an error to specify a record that's
         * longer than the fixed-length, and we never require less than
         * the fixed-length record size.
         */
        data_size = F_ISSET(data, DB_DBT_PARTIAL) ?
            __bam_partsize(dbp, op, data, h, indx) : data->size;
        padrec = 0;
        if (F_ISSET(dbp, DB_AM_FIXEDLEN)) {
                if (data_size > t->re_len) {
len_err:                __db_err(dbp->dbenv,
                            "Length improper for fixed length record %lu",
                            (u_long)data_size);
                        return (EINVAL);
                }

                /* Records that are deleted anyway needn't be padded out. */
                if (!LF_ISSET(BI_DELETED) && data_size < t->re_len) {
                        padrec = 1;
                        data_size = t->re_len;
                }
        }

        /*
         * Handle partial puts or short fixed-length records: build the
         * real record.
         */
        if (padrec || F_ISSET(data, DB_DBT_PARTIAL)) {
                tdbt = *data;
                if ((ret =
                    __bam_build(dbc, op, &tdbt, h, indx, data_size)) != 0)
                        return (ret);
                data = &tdbt;
        }

        /*
         * If the user has specified a duplicate comparison function, return
         * an error if DB_CURRENT was specified and the replacement data
         * doesn't compare equal to the current data.  This stops apps from
         * screwing up the duplicate sort order.  We have to do this after
         * we build the real record so that we're comparing the real items.
         */
        if (op == DB_CURRENT && dbp->dup_compare != NULL) {
                if ((ret = __bam_cmp(dbp, data, h,
                    indx + (TYPE(h) == P_LBTREE ? O_INDX : 0),
                    dbp->dup_compare, &cmp)) != 0)
                        return (ret);
                if (cmp != 0) {
                        __db_err(dbp->dbenv,
                            "Current data differs from put data");
                        return (EINVAL);
                }
        }

        /*
         * If the key or data item won't fit on a page, we'll have to store
         * them on overflow pages.
         */
        needed = 0;
        bigdata = data_size > cp->ovflsize;
        switch (op) {
        case DB_KEYFIRST:
                /* We're adding a new key and data pair. */
                bigkey = key->size > cp->ovflsize;
                if (bigkey)
                        needed += BOVERFLOW_PSIZE;
                else
                        needed += BKEYDATA_PSIZE(key->size);
                if (bigdata)
                        needed += BOVERFLOW_PSIZE;
                else
                        needed += BKEYDATA_PSIZE(data_size);
                break;
        case DB_AFTER:
        case DB_BEFORE:
        case DB_CURRENT:
                /*
                 * We're either overwriting the data item of a key/data pair
                 * or we're creating a new on-page duplicate and only adding
                 * a data item.
                 *
                 * !!!
                 * We're not currently correcting for space reclaimed from
                 * already deleted items, but I don't think it's worth the
                 * complexity.
                 */
                bigkey = 0;
                if (op == DB_CURRENT) {
                        bk = GET_BKEYDATA(dbp, h,
                            indx + (TYPE(h) == P_LBTREE ? O_INDX : 0));
                        if (B_TYPE(bk->type) == B_KEYDATA)
                                have_bytes = BKEYDATA_PSIZE(bk->len);
                        else
                                have_bytes = BOVERFLOW_PSIZE;
                        need_bytes = 0;
                } else {
                        have_bytes = 0;
                        need_bytes = sizeof(db_indx_t);
                }
                if (bigdata)
                        need_bytes += BOVERFLOW_PSIZE;
                else
                        need_bytes += BKEYDATA_PSIZE(data_size);

                if (have_bytes < need_bytes)
                        needed += need_bytes - have_bytes;
                break;
        default:
                return (__db_unknown_flag(dbp->dbenv, "__bam_iitem", op));
        }

        /*
         * If there's not enough room, or the user has put a ceiling on the
         * number of keys permitted in the page, split the page.
         *
         * XXX
         * The t->bt_maxkey test here may be insufficient -- do we have to
         * check in the btree split code, so we don't undo it there!?!?
         */
        if (P_FREESPACE(dbp, h) < needed ||
            (t->bt_maxkey != 0 && NUM_ENT(h) > t->bt_maxkey))
                return (DB_NEEDSPLIT);

        /*
         * The code breaks it up into five cases:
         *
         * 1. Insert a new key/data pair.
         * 2. Append a new data item (a new duplicate).
         * 3. Insert a new data item (a new duplicate).
         * 4. Delete and re-add the data item (overflow item).
         * 5. Overwrite the data item.
         */
        switch (op) {
        case DB_KEYFIRST:               /* 1. Insert a new key/data pair. */
                if (bigkey) {
                        if ((ret = __bam_ovput(dbc,
                            B_OVERFLOW, PGNO_INVALID, h, indx, key)) != 0)
                                return (ret);
                } else
                        if ((ret = __db_pitem(dbc, h, indx,
                            BKEYDATA_SIZE(key->size), NULL, key)) != 0)
                                return (ret);

                if ((ret = __bam_ca_di(dbc, PGNO(h), indx, 1)) != 0)
                        return (ret);
                ++indx;
                break;
        case DB_AFTER:                  /* 2. Append a new data item. */
                if (TYPE(h) == P_LBTREE) {
                        /* Copy the key for the duplicate and adjust cursors. */
                        if ((ret =
                            __bam_adjindx(dbc, h, indx + P_INDX, indx, 1)) != 0)
                                return (ret);
                        if ((ret =
                            __bam_ca_di(dbc, PGNO(h), indx + P_INDX, 1)) != 0)
                                return (ret);

                        indx += 3;
                        dupadjust = 1;

                        cp->indx += 2;
                } else {
                        ++indx;
                        cp->indx += 1;
                }
                break;
        case DB_BEFORE:                 /* 3. Insert a new data item. */
                if (TYPE(h) == P_LBTREE) {
                        /* Copy the key for the duplicate and adjust cursors. */
                        if ((ret = __bam_adjindx(dbc, h, indx, indx, 1)) != 0)
                                return (ret);
                        if ((ret = __bam_ca_di(dbc, PGNO(h), indx, 1)) != 0)
                                return (ret);

                        ++indx;
                        dupadjust = 1;
                }
                break;
        case DB_CURRENT:
                 /*
                  * Clear the cursor's deleted flag.  The problem is that if
                  * we deadlock or fail while deleting the overflow item or
                  * replacing the non-overflow item, a subsequent cursor close
                  * will try and remove the item because the cursor's delete
                  * flag is set
                  */
                (void)__bam_ca_delete(dbp, PGNO(h), indx, 0);

                if (TYPE(h) == P_LBTREE) {
                        ++indx;
                        dupadjust = 1;

                        /*
                         * In a Btree deleted records aren't counted (deleted
                         * records are counted in a Recno because all accesses
                         * are based on record number).  If it's a Btree and
                         * it's a DB_CURRENT operation overwriting a previously
                         * deleted record, increment the record count.
                         */
                        was_deleted = B_DISSET(bk->type);
                }

                /*
                 * 4. Delete and re-add the data item.
                 *
                 * If we're changing the type of the on-page structure, or we
                 * are referencing offpage items, we have to delete and then
                 * re-add the item.  We do not do any cursor adjustments here
                 * because we're going to immediately re-add the item into the
                 * same slot.
                 */
                if (bigdata || B_TYPE(bk->type) != B_KEYDATA) {
                        if ((ret = __bam_ditem(dbc, h, indx)) != 0)
                                return (ret);
                        break;
                }

                /* 5. Overwrite the data item. */
                replace = 1;
                break;
        default:
                return (__db_unknown_flag(dbp->dbenv, "__bam_iitem", op));
        }

        /* Add the data. */
        if (bigdata) {
                /*
                 * We do not have to handle deleted (BI_DELETED) records
                 * in this case; the actual records should never be created.
                 */
                DB_ASSERT(!LF_ISSET(BI_DELETED));
                if ((ret = __bam_ovput(dbc,
                    B_OVERFLOW, PGNO_INVALID, h, indx, data)) != 0)
                        return (ret);
        } else {
                if (LF_ISSET(BI_DELETED)) {
                        B_TSET(bk_tmp.type, B_KEYDATA, 1);
                        bk_tmp.len = data->size;
                        bk_hdr.data = &bk_tmp;
                        bk_hdr.size = SSZA(BKEYDATA, data);
                        ret = __db_pitem(dbc, h, indx,
                            BKEYDATA_SIZE(data->size), &bk_hdr, data);
                } else if (replace)
                        ret = __bam_ritem(dbc, h, indx, data);
                else
                        ret = __db_pitem(dbc, h, indx,
                            BKEYDATA_SIZE(data->size), NULL, data);
                if (ret != 0)
                        return (ret);
        }
        if ((ret = mpf->set(mpf, h, DB_MPOOL_DIRTY)) != 0)
                return (ret);

        /*
         * Re-position the cursors if necessary and reset the current cursor
         * to point to the new item.
         */
        if (op != DB_CURRENT) {
                if ((ret = __bam_ca_di(dbc, PGNO(h), indx, 1)) != 0)
                        return (ret);
                cp->indx = TYPE(h) == P_LBTREE ? indx - O_INDX : indx;
        }

        /*
         * If we've changed the record count, update the tree.  There's no
         * need to adjust the count if the operation not performed on the
         * current record or when the current record was previously deleted.
         */
        if (F_ISSET(cp, C_RECNUM) && (op != DB_CURRENT || was_deleted))
                if ((ret = __bam_adjust(dbc, 1)) != 0)
                        return (ret);

        /*
         * If a Btree leaf page is at least 50% full and we may have added or
         * modified a duplicate data item, see if the set of duplicates takes
         * up at least 25% of the space on the page.  If it does, move it onto
         * its own page.
         */
        if (dupadjust && P_FREESPACE(dbp, h) <= dbp->pgsize / 2) {
                if ((ret = __bam_dup_convert(dbc, h, indx - O_INDX)) != 0)
                        return (ret);
        }

        /* If we've modified a recno file, set the flag. */
        if (dbc->dbtype == DB_RECNO)
                t->re_modified = 1;

        return (ret);
}

/*
 * __bam_partsize --
 *      Figure out how much space a partial data item is in total.
 */
static u_int32_t
__bam_partsize(dbp, op, data, h, indx)
        DB *dbp;
        u_int32_t op, indx;
        DBT *data;
        PAGE *h;
{
        BKEYDATA *bk;
        u_int32_t nbytes;

        /*
         * If the record doesn't already exist, it's simply the data we're
         * provided.
         */
        if (op != DB_CURRENT)
                return (data->doff + data->size);

        /*
         * Otherwise, it's the data provided plus any already existing data
         * that we're not replacing.
         */
        bk = GET_BKEYDATA(dbp, h, indx + (TYPE(h) == P_LBTREE ? O_INDX : 0));
        nbytes =
            B_TYPE(bk->type) == B_OVERFLOW ? ((BOVERFLOW *)bk)->tlen : bk->len;

        return (__db_partsize(nbytes, data));
}

/*
 * __bam_build --
 *      Build the real record for a partial put, or short fixed-length record.
 */
static int
__bam_build(dbc, op, dbt, h, indx, nbytes)
        DBC *dbc;
        u_int32_t op, indx, nbytes;
        DBT *dbt;
        PAGE *h;
{
        BKEYDATA *bk, tbk;
        BOVERFLOW *bo;
        BTREE *t;
        DB *dbp;
        DBT copy, *rdata;
        u_int32_t len, tlen;
        u_int8_t *p;
        int ret;

        COMPQUIET(bo, NULL);

        dbp = dbc->dbp;
        t = dbp->bt_internal;

        /* We use the record data return memory, it's only a short-term use. */
        rdata = &dbc->my_rdata;
        if (rdata->ulen < nbytes) {
                if ((ret = __os_realloc(dbp->dbenv,
                    nbytes, &rdata->data)) != 0) {
                        rdata->ulen = 0;
                        rdata->data = NULL;
                        return (ret);
                }
                rdata->ulen = nbytes;
        }

        /*
         * We use nul or pad bytes for any part of the record that isn't
         * specified; get it over with.
         */
        memset(rdata->data,
           F_ISSET(dbp, DB_AM_FIXEDLEN) ? t->re_pad : 0, nbytes);

        /*
         * In the next clauses, we need to do three things: a) set p to point
         * to the place at which to copy the user's data, b) set tlen to the
         * total length of the record, not including the bytes contributed by
         * the user, and c) copy any valid data from an existing record.  If
         * it's not a partial put (this code is called for both partial puts
         * and fixed-length record padding) or it's a new key, we can cut to
         * the chase.
         */
        if (!F_ISSET(dbt, DB_DBT_PARTIAL) || op != DB_CURRENT) {
                p = (u_int8_t *)rdata->data + dbt->doff;
                tlen = dbt->doff;
                goto user_copy;
        }

        /* Find the current record. */
        if (indx < NUM_ENT(h)) {
                bk = GET_BKEYDATA(dbp, h, indx + (TYPE(h) == P_LBTREE ?
                    O_INDX : 0));
                bo = (BOVERFLOW *)bk;
        } else {
                bk = &tbk;
                B_TSET(bk->type, B_KEYDATA, 0);
                bk->len = 0;
        }
        if (B_TYPE(bk->type) == B_OVERFLOW) {
                /*
                 * In the case of an overflow record, we shift things around
                 * in the current record rather than allocate a separate copy.
                 */
                memset(&copy, 0, sizeof(copy));
                if ((ret = __db_goff(dbp, &copy, bo->tlen,
                    bo->pgno, &rdata->data, &rdata->ulen)) != 0)
                        return (ret);

                /* Skip any leading data from the original record. */
                tlen = dbt->doff;
                p = (u_int8_t *)rdata->data + dbt->doff;

                /*
                 * Copy in any trailing data from the original record.
                 *
                 * If the original record was larger than the original offset
                 * plus the bytes being deleted, there is trailing data in the
                 * original record we need to preserve.  If we aren't deleting
                 * the same number of bytes as we're inserting, copy it up or
                 * down, into place.
                 *
                 * Use memmove(), the regions may overlap.
                 */
                if (bo->tlen > dbt->doff + dbt->dlen) {
                        len = bo->tlen - (dbt->doff + dbt->dlen);
                        if (dbt->dlen != dbt->size)
                                memmove(p + dbt->size, p + dbt->dlen, len);
                        tlen += len;
                }
        } else {
                /* Copy in any leading data from the original record. */
                memcpy(rdata->data,
                    bk->data, dbt->doff > bk->len ? bk->len : dbt->doff);
                tlen = dbt->doff;
                p = (u_int8_t *)rdata->data + dbt->doff;

                /* Copy in any trailing data from the original record. */
                len = dbt->doff + dbt->dlen;
                if (bk->len > len) {
                        memcpy(p + dbt->size, bk->data + len, bk->len - len);
                        tlen += bk->len - len;
                }
        }

user_copy:
        /*
         * Copy in the application provided data -- p and tlen must have been
         * initialized above.
         */
        memcpy(p, dbt->data, dbt->size);
        tlen += dbt->size;

        /* Set the DBT to reference our new record. */
        rdata->size = F_ISSET(dbp, DB_AM_FIXEDLEN) ? t->re_len : tlen;
        rdata->dlen = 0;
        rdata->doff = 0;
        rdata->flags = 0;
        *dbt = *rdata;
        return (0);
}

/*
 * __bam_ritem --
 *      Replace an item on a page.
 *
 * PUBLIC: int __bam_ritem __P((DBC *, PAGE *, u_int32_t, DBT *));
 */
int
__bam_ritem(dbc, h, indx, data)
        DBC *dbc;
        PAGE *h;
        u_int32_t indx;
        DBT *data;
{
        BKEYDATA *bk;
        DB *dbp;
        DBT orig, repl;
        db_indx_t cnt, lo, ln, min, off, prefix, suffix;
        int32_t nbytes;
        int ret;
        db_indx_t *inp;
        u_int8_t *p, *t;

        dbp = dbc->dbp;

        /*
         * Replace a single item onto a page.  The logic figuring out where
         * to insert and whether it fits is handled in the caller.  All we do
         * here is manage the page shuffling.
         */
        bk = GET_BKEYDATA(dbp, h, indx);

        /* Log the change. */
        if (DBC_LOGGING(dbc)) {
                /*
                 * We might as well check to see if the two data items share
                 * a common prefix and suffix -- it can save us a lot of log
                 * message if they're large.
                 */
                min = data->size < bk->len ? data->size : bk->len;
                for (prefix = 0,
                    p = bk->data, t = data->data;
                    prefix < min && *p == *t; ++prefix, ++p, ++t)
                        ;

                min -= prefix;
                for (suffix = 0,
                    p = (u_int8_t *)bk->data + bk->len - 1,
                    t = (u_int8_t *)data->data + data->size - 1;
                    suffix < min && *p == *t; ++suffix, --p, --t)
                        ;

                /* We only log the parts of the keys that have changed. */
                orig.data = (u_int8_t *)bk->data + prefix;
                orig.size = bk->len - (prefix + suffix);
                repl.data = (u_int8_t *)data->data + prefix;
                repl.size = data->size - (prefix + suffix);
                if ((ret = __bam_repl_log(dbp, dbc->txn, &LSN(h), 0, PGNO(h),
                    &LSN(h), (u_int32_t)indx, (u_int32_t)B_DISSET(bk->type),
                    &orig, &repl, (u_int32_t)prefix, (u_int32_t)suffix)) != 0)
                        return (ret);
        } else
                LSN_NOT_LOGGED(LSN(h));

        /*
         * Set references to the first in-use byte on the page and the
         * first byte of the item being replaced.
         */
        inp = P_INP(dbp, h);
        p = (u_int8_t *)h + HOFFSET(h);
        t = (u_int8_t *)bk;

        /*
         * If the entry is growing in size, shift the beginning of the data
         * part of the page down.  If the entry is shrinking in size, shift
         * the beginning of the data part of the page up.  Use memmove(3),
         * the regions overlap.
         */
        lo = BKEYDATA_SIZE(bk->len);
        ln = (db_indx_t)BKEYDATA_SIZE(data->size);
        if (lo != ln) {
                nbytes = lo - ln;               /* Signed difference. */
                if (p == t)                     /* First index is fast. */
                        inp[indx] += nbytes;
                else {                          /* Else, shift the page. */
                        memmove(p + nbytes, p, t - p);

                        /* Adjust the indices' offsets. */
                        off = inp[indx];
                        for (cnt = 0; cnt < NUM_ENT(h); ++cnt)
                                if (inp[cnt] <= off)
                                        inp[cnt] += nbytes;
                }

                /* Clean up the page and adjust the item's reference. */
                HOFFSET(h) += nbytes;
                t += nbytes;
        }

        /* Copy the new item onto the page. */
        bk = (BKEYDATA *)t;
        B_TSET(bk->type, B_KEYDATA, 0);
        bk->len = data->size;
        memcpy(bk->data, data->data, data->size);

        return (0);
}

/*
 * __bam_dup_convert --
 *      Check to see if the duplicate set at indx should have its own page.
 *      If it should, create it.
 */
static int
__bam_dup_convert(dbc, h, indx)
        DBC *dbc;
        PAGE *h;
        u_int32_t indx;
{
        BKEYDATA *bk;
        DB *dbp;
        DBT hdr;
        DB_MPOOLFILE *mpf;
        PAGE *dp;
        db_indx_t cnt, cpindx, dindx, first, *inp, sz;
        int ret;

        dbp = dbc->dbp;
        mpf = dbp->mpf;
        inp = P_INP(dbp, h);

        /*
         * Count the duplicate records and calculate how much room they're
         * using on the page.
         */
        while (indx > 0 && inp[indx] == inp[indx - P_INDX])
                indx -= P_INDX;
        for (cnt = 0, sz = 0, first = indx;; ++cnt, indx += P_INDX) {
                if (indx >= NUM_ENT(h) || inp[first] != inp[indx])
                        break;
                bk = GET_BKEYDATA(dbp, h, indx);
                sz += B_TYPE(bk->type) == B_KEYDATA ?
                    BKEYDATA_PSIZE(bk->len) : BOVERFLOW_PSIZE;
                bk = GET_BKEYDATA(dbp, h, indx + O_INDX);
                sz += B_TYPE(bk->type) == B_KEYDATA ?
                    BKEYDATA_PSIZE(bk->len) : BOVERFLOW_PSIZE;
        }

        /*
         * We have to do these checks when the user is replacing the cursor's
         * data item -- if the application replaces a duplicate item with a
         * larger data item, it can increase the amount of space used by the
         * duplicates, requiring this check.  But that means we may have done
         * this check when it wasn't a duplicate item after all.
         */
        if (cnt == 1)
                return (0);

        /*
         * If this set of duplicates is using more than 25% of the page, move
         * them off.  The choice of 25% is a WAG, but the value must be small
         * enough that we can always split a page without putting duplicates
         * on two different pages.
         */
        if (sz < dbp->pgsize / 4)
                return (0);

        /* Get a new page. */
        if ((ret = __db_new(dbc,
            dbp->dup_compare == NULL ? P_LRECNO : P_LDUP, &dp)) != 0)
                return (ret);
        P_INIT(dp, dbp->pgsize, dp->pgno,
            PGNO_INVALID, PGNO_INVALID, LEAFLEVEL, TYPE(dp));

        /*
         * Move this set of duplicates off the page.  First points to the first
         * key of the first duplicate key/data pair, cnt is the number of pairs
         * we're dealing with.
         */
        memset(&hdr, 0, sizeof(hdr));
        dindx = first;
        indx = first;
        cpindx = 0;
        do {
                /* Move cursors referencing the old entry to the new entry. */
                if ((ret = __bam_ca_dup(dbc, first,
                    PGNO(h), indx, PGNO(dp), cpindx)) != 0)
                        goto err;

                /*
                 * Copy the entry to the new page.  If the off-duplicate page
                 * If the off-duplicate page is a Btree page (i.e. dup_compare
                 * will be non-NULL, we use Btree pages for sorted dups,
                 * and Recno pages for unsorted dups), move all entries
                 * normally, even deleted ones.  If it's a Recno page,
                 * deleted entries are discarded (if the deleted entry is
                 * overflow, then free up those pages).
                 */
                bk = GET_BKEYDATA(dbp, h, dindx + 1);
                hdr.data = bk;
                hdr.size = B_TYPE(bk->type) == B_KEYDATA ?
                    BKEYDATA_SIZE(bk->len) : BOVERFLOW_SIZE;
                if (dbp->dup_compare == NULL && B_DISSET(bk->type)) {
                        /*
                         * Unsorted dups, i.e. recno page, and we have
                         * a deleted entry, don't move it, but if it was
                         * an overflow entry, we need to free those pages.
                         */
                        if (B_TYPE(bk->type) == B_OVERFLOW &&
                            (ret = __db_doff(dbc,
                            (GET_BOVERFLOW(dbp, h, dindx + 1))->pgno)) != 0)
                                goto err;
                } else {
                        if ((ret = __db_pitem(
                            dbc, dp, cpindx, hdr.size, &hdr, NULL)) != 0)
                                goto err;
                        ++cpindx;
                }
                /* Delete all but the last reference to the key. */
                if (cnt != 1) {
                        if ((ret = __bam_adjindx(dbc,
                            h, dindx, first + 1, 0)) != 0)
                                goto err;
                } else
                        dindx++;

                /* Delete the data item. */
                if ((ret = __db_ditem(dbc, h, dindx, hdr.size)) != 0)
                        goto err;
                indx += P_INDX;
        } while (--cnt);

        /* Put in a new data item that points to the duplicates page. */
        if ((ret = __bam_ovput(dbc,
            B_DUPLICATE, dp->pgno, h, first + 1, NULL)) != 0)
                goto err;

        /* Adjust cursors for all the above movments. */
        if ((ret = __bam_ca_di(dbc,
            PGNO(h), first + P_INDX, first + P_INDX - indx)) != 0)
                goto err;

        return (mpf->put(mpf, dp, DB_MPOOL_DIRTY));

err:    (void)mpf->put(mpf, dp, 0);
        return (ret);
}

/*
 * __bam_ovput --
 *      Build an item for an off-page duplicates page or overflow page and
 *      insert it on the page.
 */
static int
__bam_ovput(dbc, type, pgno, h, indx, item)
        DBC *dbc;
        u_int32_t type, indx;
        db_pgno_t pgno;
        PAGE *h;
        DBT *item;
{
        BOVERFLOW bo;
        DBT hdr;
        int ret;

        UMRW_SET(bo.unused1);
        B_TSET(bo.type, type, 0);
        UMRW_SET(bo.unused2);

        /*
         * If we're creating an overflow item, do so and acquire the page
         * number for it.  If we're creating an off-page duplicates tree,
         * we are giving the page number as an argument.
         */
        if (type == B_OVERFLOW) {
                if ((ret = __db_poff(dbc, item, &bo.pgno)) != 0)
                        return (ret);
                bo.tlen = item->size;
        } else {
                bo.pgno = pgno;
                bo.tlen = 0;
        }

        /* Store the new record on the page. */
        memset(&hdr, 0, sizeof(hdr));
        hdr.data = &bo;
        hdr.size = BOVERFLOW_SIZE;
        return (__db_pitem(dbc, h, indx, BOVERFLOW_SIZE, &hdr, NULL));
}

---