db/btree/bt_put.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *  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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *  This product includes software developed by the University of
 *  California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)bt_put.c  10.54 (Sleepycat) 12/6/98";
#endif /* not lint */

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

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

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

static int __bam_fixed __P((DBC *, DBT *));
static int __bam_ndup __P((DBC *, PAGE *, u_int32_t));
static int __bam_ovput __P((DBC *, PAGE *, u_int32_t, DBT *));
static int __bam_partial __P((DBC *,
    DBT *, PAGE *, u_int32_t, u_int32_t, u_int32_t));
static u_int32_t __bam_partsize __P((DBT *, PAGE *, u_int32_t));

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

    COMPQUIET(bk, NULL);

    dbp = dbc->dbp;
    t = dbp->internal;
    h = *hp;
    indx = *indxp;
    dupadjust = replace = 0;

    /*
     * If it's a page of duplicates, call the common code to do the work.
     *
     * !!!
     * Here's where the hp and indxp are important.  The duplicate code
     * may decide to rework/rearrange the pages and indices we're using,
     * so the caller must understand that the page stack may change.
     */
    if (TYPE(h) == P_DUPLICATE) {
        /* Adjust the index for the new item if it's a DB_AFTER op. */
        if (op == DB_AFTER)
            ++*indxp;

        /* Remove the current item if it's a DB_CURRENT op. */
        if (op == DB_CURRENT) {
            bk = GET_BKEYDATA(*hp, *indxp);
            switch (B_TYPE(bk->type)) {
            case B_KEYDATA:
                nbytes = BKEYDATA_SIZE(bk->len);
                break;
            case B_OVERFLOW:
                nbytes = BOVERFLOW_SIZE;
                break;
            default:
                return (__db_pgfmt(dbp, h->pgno));
            }
            if ((ret = __db_ditem(dbc, *hp, *indxp, nbytes)) != 0)
                return (ret);
        }

        /* Put the new/replacement item onto the page. */
        if ((ret = __db_dput(dbc, data, hp, indxp, __bam_new)) != 0)
            return (ret);

        goto done;
    }

    /* Handle fixed-length records: build the real record. */
    if (F_ISSET(dbp, DB_RE_FIXEDLEN) && data->size != t->recno->re_len) {
        tdbt = *data;
        if ((ret = __bam_fixed(dbc, &tdbt)) != 0)
            return (ret);
        data = &tdbt;
    }

    /*
     * Figure out how much space the data will take, including if it's a
     * partial record.  If either of the key or data items won't fit on
     * a page, we'll have to store them on overflow pages.
     */
    bigkey = LF_ISSET(BI_NEWKEY) && key->size > t->bt_ovflsize;
    data_size = F_ISSET(data, DB_DBT_PARTIAL) ?
        __bam_partsize(data, h, indx) : data->size;
    bigdata = data_size > t->bt_ovflsize;

    needed = 0;
    if (LF_ISSET(BI_NEWKEY)) {
        /* If BI_NEWKEY is set we're adding a new key and data pair. */
        if (bigkey)
            needed += BOVERFLOW_PSIZE;
        else
            needed += BKEYDATA_PSIZE(key->size);
        if (bigdata)
            needed += BOVERFLOW_PSIZE;
        else
            needed += BKEYDATA_PSIZE(data_size);
    } else {
        /*
         * We're either overwriting the data item of a key/data pair
         * or we're adding the data item only, i.e. a new duplicate.
         */
        if (op == DB_CURRENT) {
            bk = GET_BKEYDATA(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;
    }

    /*
     * 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(h) < needed ||
        (t->bt_maxkey != 0 && NUM_ENT(h) > t->bt_maxkey))
        return (DB_NEEDSPLIT);

    /* Handle partial puts: build the real record. */
    if (F_ISSET(data, DB_DBT_PARTIAL)) {
        tdbt = *data;
        if ((ret = __bam_partial(dbc,
            &tdbt, h, indx, data_size, flags)) != 0)
            return (ret);
        data = &tdbt;
    }

    /*
     * The code breaks it up into six cases:
     *
     * 1. Append a new key/data pair.
     * 2. Insert a new key/data pair.
     * 3. Append a new data item (a new duplicate).
     * 4. Insert a new data item (a new duplicate).
     * 5. Overflow item: delete and re-add the data item.
     * 6. Replace the data item.
     */
    if (LF_ISSET(BI_NEWKEY)) {
        switch (op) {
        case DB_AFTER:      /* 1. Append a new key/data pair. */
            indx += 2;
            *indxp += 2;
            break;
        case DB_BEFORE:     /* 2. Insert a new key/data pair. */
            break;
        default:
            return (EINVAL);
        }

        /* Add the key. */
        if (bigkey) {
            if ((ret = __bam_ovput(dbc, h, indx, key)) != 0)
                return (ret);
        } else
            if ((ret = __db_pitem(dbc, h, indx,
                BKEYDATA_SIZE(key->size), NULL, key)) != 0)
                return (ret);
        ++indx;
    } else {
        switch (op) {
        case DB_AFTER:      /* 3. Append a new data item. */
            if (TYPE(h) == P_LBTREE) {
                /*
                 * Adjust the cursor and copy in the key for
                 * the duplicate.
                 */
                if ((ret = __bam_adjindx(dbc,
                    h, indx + P_INDX, indx, 1)) != 0)
                    return (ret);

                indx += 3;
                dupadjust = 1;

                *indxp += 2;
            } else {
                ++indx;
                __bam_ca_di(dbp, h->pgno, indx, 1);

                *indxp += 1;
            }
            break;
        case DB_BEFORE:     /* 4. Insert a new data item. */
            if (TYPE(h) == P_LBTREE) {
                /*
                 * Adjust the cursor and copy in the key for
                 * the duplicate.
                 */
                if ((ret =
                    __bam_adjindx(dbc, h, indx, indx, 1)) != 0)
                    return (ret);

                ++indx;
                dupadjust = 1;
            } else
                __bam_ca_di(dbp, h->pgno, indx, 1);
            break;
        case DB_CURRENT:
            if (TYPE(h) == P_LBTREE)
                ++indx;

            /*
             * 5. Delete/re-add the data item.
             *
             * If we're dealing with offpage items, we have to
             * delete and then re-add the item.
             */
            if (bigdata || B_TYPE(bk->type) != B_KEYDATA) {
                if ((ret = __bam_ditem(dbc, h, indx)) != 0)
                    return (ret);
                break;
            }

            /* 6. Replace the data item. */
            replace = 1;
            break;
        default:
            return (EINVAL);
        }
    }

    /* Add the data. */
    if (bigdata) {
        if ((ret = __bam_ovput(dbc, h, indx, data)) != 0)
            return (ret);
    } else {
        BKEYDATA __bk;
        DBT __hdr;

        if (LF_ISSET(BI_DELETED)) {
            B_TSET(__bk.type, B_KEYDATA, 1);
            __bk.len = data->size;
            __hdr.data = &__bk;
            __hdr.size = SSZA(BKEYDATA, data);
            ret = __db_pitem(dbc, h, indx,
                BKEYDATA_SIZE(data->size), &__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 = memp_fset(dbp->mpf, h, DB_MPOOL_DIRTY)) != 0)
        return (ret);

    /*
     * If the page is at least 50% full, and we added a duplicate, see if
     * that set of duplicates takes up at least 25% of the space.  If it
     * does, move it off onto its own page.
     */
    if (dupadjust && P_FREESPACE(h) <= dbp->pgsize / 2) {
        --indx;
        if ((ret = __bam_ndup(dbc, h, indx)) != 0)
            return (ret);
    }

    /*
     * If we've changed the record count, update the tree.  Record counts
     * need to be updated in recno databases and in btree databases where
     * we are supporting records.  In both cases, adjust the count if the
     * operation wasn't performed on the current record or when the caller
     * overrides and wants the adjustment made regardless.
     */
done:   if (LF_ISSET(BI_DOINCR) ||
        (op != DB_CURRENT &&
        (F_ISSET(dbp, DB_BT_RECNUM) || dbp->type == DB_RECNO)))
        if ((ret = __bam_adjust(dbc, 1)) != 0)
            return (ret);

    /* If we've modified a recno file, set the flag */
    if (t->recno != NULL)
        F_SET(t->recno, RECNO_MODIFIED);

    return (ret);
}

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

    /*
     * Figure out how much total space we'll need.  If the record doesn't
     * already exist, it's simply the data we're provided.
     */
    if (indx >= NUM_ENT(h))
        return (data->doff + data->size);

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

    /*
     * There are really two cases here:
     *
     * Case 1: We are replacing some bytes that do not exist (i.e., they
     * are past the end of the record).  In this case the number of bytes
     * we are replacing is irrelevant and all we care about is how many
     * bytes we are going to add from offset.  So, the new record length
     * is going to be the size of the new bytes (size) plus wherever those
     * new bytes begin (doff).
     *
     * Case 2: All the bytes we are replacing exist.  Therefore, the new
     * size is the oldsize (nbytes) minus the bytes we are replacing (dlen)
     * plus the bytes we are adding (size).
     */
    if (nbytes < data->doff + data->dlen)       /* Case 1 */
        return (data->doff + data->size);

    return (nbytes + data->size - data->dlen);  /* Case 2 */
}

/*
 * OVPUT --
 *  Copy an overflow item onto a page.
 */
#undef  OVPUT
#define OVPUT(h, indx, bo) do {                     \
    DBT __hdr;                          \
    memset(&__hdr, 0, sizeof(__hdr));               \
    __hdr.data = &bo;                       \
    __hdr.size = BOVERFLOW_SIZE;                    \
    if ((ret = __db_pitem(dbc,                  \
        h, indx, BOVERFLOW_SIZE, &__hdr, NULL)) != 0)       \
        return (ret);                       \
} while (0)

/*
 * __bam_ovput --
 *  Build an overflow item and put it on the page.
 */
static int
__bam_ovput(dbc, h, indx, item)
    DBC *dbc;
    PAGE *h;
    u_int32_t indx;
    DBT *item;
{
    BOVERFLOW bo;
    int ret;

    UMRW(bo.unused1);
    B_TSET(bo.type, B_OVERFLOW, 0);
    UMRW(bo.unused2);
    if ((ret = __db_poff(dbc, item, &bo.pgno, __bam_new)) != 0)
        return (ret);
    bo.tlen = item->size;

    OVPUT(h, indx, bo);

    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;
    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(h, indx);

    /* Log the change. */
    if (DB_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->dbenv->lg_info, dbc->txn,
            &LSN(h), 0, dbp->log_fileid, 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);
    }

    /*
     * Set references to the first in-use byte on the page and the
     * first byte of the item being replaced.
     */
    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 = BKEYDATA_SIZE(data->size);
    if (lo != ln) {
        nbytes = lo - ln;       /* Signed difference. */
        if (p == t)         /* First index is fast. */
            h->inp[indx] += nbytes;
        else {              /* Else, shift the page. */
            memmove(p + nbytes, p, t - p);

            /* Adjust the indices' offsets. */
            off = h->inp[indx];
            for (cnt = 0; cnt < NUM_ENT(h); ++cnt)
                if (h->inp[cnt] <= off)
                    h->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_ndup --
 *  Check to see if the duplicate set at indx should have its own page.
 *  If it should, create it.
 */
static int
__bam_ndup(dbc, h, indx)
    DBC *dbc;
    PAGE *h;
    u_int32_t indx;
{
    BKEYDATA *bk;
    BOVERFLOW bo;
    DB *dbp;
    DBT hdr;
    PAGE *cp;
    db_indx_t cnt, cpindx, first, sz;
    int ret;

    dbp = dbc->dbp;

    while (indx > 0 && h->inp[indx] == h->inp[indx - P_INDX])
        indx -= P_INDX;
    for (cnt = 0, sz = 0, first = indx;; ++cnt, indx += P_INDX) {
        if (indx >= NUM_ENT(h) || h->inp[first] != h->inp[indx])
            break;
        bk = GET_BKEYDATA(h, indx);
        sz += B_TYPE(bk->type) == B_KEYDATA ?
            BKEYDATA_PSIZE(bk->len) : BOVERFLOW_PSIZE;
        bk = GET_BKEYDATA(h, indx + O_INDX);
        sz += B_TYPE(bk->type) == B_KEYDATA ?
            BKEYDATA_PSIZE(bk->len) : BOVERFLOW_PSIZE;
    }

    /*
     * If this set of duplicates is using more than 25% of the page, move
     * them off.  The choice of 25% is a WAG, but it has to be small enough
     * that we can always split regardless of the presence of duplicates.
     */
    if (sz < dbp->pgsize / 4)
        return (0);

    /* Get a new page. */
    if ((ret = __bam_new(dbc, P_DUPLICATE, &cp)) != 0)
        return (ret);

    /*
     * 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));
    for (indx = first + O_INDX, cpindx = 0;; ++cpindx) {
        /* Copy the entry to the new page. */
        bk = GET_BKEYDATA(h, indx);
        hdr.data = bk;
        hdr.size = B_TYPE(bk->type) == B_KEYDATA ?
            BKEYDATA_SIZE(bk->len) : BOVERFLOW_SIZE;
        if ((ret =
            __db_pitem(dbc, cp, cpindx, hdr.size, &hdr, NULL)) != 0)
            goto err;

        /*
         * Move cursors referencing the old entry to the new entry.
         * Done after the page put because __db_pitem() adjusts
         * cursors on the new page, and before the delete because
         * __db_ditem adjusts cursors on the old page.
         */
        __bam_ca_dup(dbp,
            PGNO(h), first, indx - O_INDX, PGNO(cp), cpindx);

        /* Delete the data item. */
        if ((ret = __db_ditem(dbc, h, indx, hdr.size)) != 0)
            goto err;

        /* Delete all but the first reference to the key. */
        if (--cnt == 0)
            break;
        if ((ret = __bam_adjindx(dbc, h, indx, first, 0)) != 0)
            goto err;
    }

    /* Put in a new data item that points to the duplicates page. */
    UMRW(bo.unused1);
    B_TSET(bo.type, B_DUPLICATE, 0);
    UMRW(bo.unused2);
    bo.pgno = cp->pgno;
    bo.tlen = 0;

    OVPUT(h, indx, bo);

    return (memp_fput(dbp->mpf, cp, DB_MPOOL_DIRTY));

err:    (void)__bam_free(dbc, cp);
    return (ret);
}

/*
 * __bam_fixed --
 *  Build the real record for a fixed length put.
 */
static int
__bam_fixed(dbc, dbt)
    DBC *dbc;
    DBT *dbt;
{
    DB *dbp;
    RECNO *rp;
    int ret;

    dbp = dbc->dbp;
    rp = ((BTREE *)dbp->internal)->recno;

    /*
     * If database contains fixed-length records, and the record is long,
     * return EINVAL.
     */
    if (dbt->size > rp->re_len)
        return (EINVAL);

    /*
     * The caller checked to see if it was just right, so we know it's
     * short.  Pad it out.  We use the record data return memory, it's
     * only a short-term use.
     */
    if (dbc->rdata.ulen < rp->re_len) {
         if ((ret = __os_realloc(&dbc->rdata.data, rp->re_len)) != 0) {
            dbc->rdata.ulen = 0;
            dbc->rdata.data = NULL;
            return (ret);
        }
        dbc->rdata.ulen = rp->re_len;
    }
    memcpy(dbc->rdata.data, dbt->data, dbt->size);
    memset((u_int8_t *)dbc->rdata.data + dbt->size,
        rp->re_pad, rp->re_len - dbt->size);

    /*
     * Clean up our flags and other information just in case, and
     * change the caller's DBT to reference our created record.
     */
    dbc->rdata.size = rp->re_len;
    dbc->rdata.dlen = 0;
    dbc->rdata.doff = 0;
    dbc->rdata.flags = 0;
    *dbt = dbc->rdata;

    return (0);
}

/*
 * __bam_partial --
 *  Build the real record for a partial put.
 */
static int
__bam_partial(dbc, dbt, h, indx, nbytes, flags)
    DBC *dbc;
    DBT *dbt;
    PAGE *h;
    u_int32_t indx, nbytes, flags;
{
    BKEYDATA *bk, tbk;
    BOVERFLOW *bo;
    DB *dbp;
    DBT copy;
    u_int32_t len, tlen;
    u_int8_t *p;
    int ret;

    COMPQUIET(bo, NULL);

    dbp = dbc->dbp;

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

    /*
     * We use nul bytes for any part of the record that isn't specified;
     * get it over with.
     */
    memset(dbc->rdata.data, 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 (LF_ISSET(BI_NEWKEY)) {
        tlen = dbt->doff;
        p = (u_int8_t *)dbc->rdata.data + dbt->doff;
        goto ucopy;
    }

    /* Find the current record. */
    if (indx < NUM_ENT(h)) {
        bk = GET_BKEYDATA(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, &dbc->rdata.data, &dbc->rdata.ulen)) != 0)
            return (ret);

        /* Skip any leading data from the original record. */
        tlen = dbt->doff;
        p = (u_int8_t *)dbc->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(dbc->rdata.data,
            bk->data, dbt->doff > bk->len ? bk->len : dbt->doff);
        tlen = dbt->doff;
        p = (u_int8_t *)dbc->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;
        }
    }

ucopy:  /*
     * 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. */
    dbc->rdata.size = tlen;
    dbc->rdata.dlen = 0;
    dbc->rdata.doff = 0;
    dbc->rdata.flags = 0;
    *dbt = dbc->rdata;
    return (0);
}