bt_split.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.
 *
 * 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: bt_split.c,v 12.4 2005/06/16 20:20:22 bostic Exp $
 */

#include "db_config.h"

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.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/btree.h"

static int __bam_broot __P((DBC *, PAGE *, PAGE *, PAGE *));
static int __bam_page __P((DBC *, EPG *, EPG *));
static int __bam_psplit __P((DBC *, EPG *, PAGE *, PAGE *, db_indx_t *));
static int __bam_root __P((DBC *, EPG *));
static int __ram_root __P((DBC *, PAGE *, PAGE *, PAGE *));

/*
 * __bam_split --
 *      Split a page.
 *
 * PUBLIC: int __bam_split __P((DBC *, void *, db_pgno_t *));
 */
int
__bam_split(dbc, arg, root_pgnop)
        DBC *dbc;
        void *arg;
        db_pgno_t *root_pgnop;
{
        BTREE_CURSOR *cp;
        enum { UP, DOWN } dir;
        db_pgno_t root_pgno;
        int exact, level, ret;

        cp = (BTREE_CURSOR *)dbc->internal;
        root_pgno = cp->root;

        /*
         * The locking protocol we use to avoid deadlock to acquire locks by
         * walking down the tree, but we do it as lazily as possible, locking
         * the root only as a last resort.  We expect all stack pages to have
         * been discarded before we're called; we discard all short-term locks.
         *
         * When __bam_split is first called, we know that a leaf page was too
         * full for an insert.  We don't know what leaf page it was, but we
         * have the key/recno that caused the problem.  We call XX_search to
         * reacquire the leaf page, but this time get both the leaf page and
         * its parent, locked.  We then split the leaf page and see if the new
         * internal key will fit into the parent page.  If it will, we're done.
         *
         * If it won't, we discard our current locks and repeat the process,
         * only this time acquiring the parent page and its parent, locked.
         * This process repeats until we succeed in the split, splitting the
         * root page as the final resort.  The entire process then repeats,
         * as necessary, until we split a leaf page.
         *
         * XXX
         * A traditional method of speeding this up is to maintain a stack of
         * the pages traversed in the original search.  You can detect if the
         * stack is correct by storing the page's LSN when it was searched and
         * comparing that LSN with the current one when it's locked during the
         * split.  This would be an easy change for this code, but I have no
         * numbers that indicate it's worthwhile.
         */
        for (dir = UP, level = LEAFLEVEL;; dir == UP ? ++level : --level) {
                /*
                 * Acquire a page and its parent, locked.
                 */
                if ((ret = (dbc->dbtype == DB_BTREE ?
                    __bam_search(dbc, PGNO_INVALID,
                        arg, S_WRPAIR, level, NULL, &exact) :
                    __bam_rsearch(dbc,
                        (db_recno_t *)arg, S_WRPAIR, level, &exact))) != 0)
                        break;

                if (root_pgnop != NULL)
                        *root_pgnop = cp->csp[0].page->pgno == root_pgno ?
                            root_pgno : cp->csp[-1].page->pgno;
                /*
                 * Split the page if it still needs it (it's possible another
                 * thread of control has already split the page).  If we are
                 * guaranteed that two items will fit on the page, the split
                 * is no longer necessary.
                 */
                if (2 * B_MAXSIZEONPAGE(cp->ovflsize)
                    <= (db_indx_t)P_FREESPACE(dbc->dbp, cp->csp[0].page)) {
                        __bam_stkrel(dbc, STK_NOLOCK);
                        break;
                }
                ret = cp->csp[0].page->pgno == root_pgno ?
                    __bam_root(dbc, &cp->csp[0]) :
                    __bam_page(dbc, &cp->csp[-1], &cp->csp[0]);
                BT_STK_CLR(cp);

                switch (ret) {
                case 0:
                        /* Once we've split the leaf page, we're done. */
                        if (level == LEAFLEVEL)
                                return (0);

                        /* Switch directions. */
                        if (dir == UP)
                                dir = DOWN;
                        break;
                case DB_NEEDSPLIT:
                        /*
                         * It's possible to fail to split repeatedly, as other
                         * threads may be modifying the tree, or the page usage
                         * is sufficiently bad that we don't get enough space
                         * the first time.
                         */
                        if (dir == DOWN)
                                dir = UP;
                        break;
                default:
                        goto err;
                }
        }

err:    if (root_pgnop != NULL)
                *root_pgnop = cp->root;
        return (ret);
}

/*
 * __bam_root --
 *      Split the root page of a btree.
 */
static int
__bam_root(dbc, cp)
        DBC *dbc;
        EPG *cp;
{
        DB *dbp;
        DBT log_dbt;
        DB_LSN log_lsn;
        DB_MPOOLFILE *mpf;
        PAGE *lp, *rp;
        db_indx_t split;
        u_int32_t opflags;
        int ret, t_ret;

        dbp = dbc->dbp;
        mpf = dbp->mpf;
        lp = rp = NULL;

        /* Yeah, right. */
        if (cp->page->level >= MAXBTREELEVEL) {
                __db_err(dbp->dbenv,
                    "Too many btree levels: %d", cp->page->level);
                ret = ENOSPC;
                goto err;
        }

        /* Create new left and right pages for the split. */
        if ((ret = __db_new(dbc, TYPE(cp->page), &lp)) != 0 ||
            (ret = __db_new(dbc, TYPE(cp->page), &rp)) != 0)
                goto err;
        P_INIT(lp, dbp->pgsize, lp->pgno,
            PGNO_INVALID, ISINTERNAL(cp->page) ? PGNO_INVALID : rp->pgno,
            cp->page->level, TYPE(cp->page));
        P_INIT(rp, dbp->pgsize, rp->pgno,
            ISINTERNAL(cp->page) ?  PGNO_INVALID : lp->pgno, PGNO_INVALID,
            cp->page->level, TYPE(cp->page));

        /* Split the page. */
        if ((ret = __bam_psplit(dbc, cp, lp, rp, &split)) != 0)
                goto err;

        /* Log the change. */
        if (DBC_LOGGING(dbc)) {
                memset(&log_dbt, 0, sizeof(log_dbt));
                log_dbt.data = cp->page;
                log_dbt.size = dbp->pgsize;
                ZERO_LSN(log_lsn);
                opflags = F_ISSET(
                    (BTREE_CURSOR *)dbc->internal, C_RECNUM) ? SPL_NRECS : 0;
                if ((ret = __bam_split_log(dbp,
                    dbc->txn, &LSN(cp->page), 0, PGNO(lp), &LSN(lp), PGNO(rp),
                    &LSN(rp), (u_int32_t)NUM_ENT(lp), 0, &log_lsn,
                    dbc->internal->root, &log_dbt, opflags)) != 0)
                        goto err;
        } else
                LSN_NOT_LOGGED(LSN(cp->page));
        LSN(lp) = LSN(cp->page);
        LSN(rp) = LSN(cp->page);

        /* Clean up the new root page. */
        if ((ret = (dbc->dbtype == DB_RECNO ?
            __ram_root(dbc, cp->page, lp, rp) :
            __bam_broot(dbc, cp->page, lp, rp))) != 0)
                goto err;

        /* Adjust any cursors. */
        ret = __bam_ca_split(dbc, cp->page->pgno, lp->pgno, rp->pgno, split, 1);

        /* Success or error: release pages and locks. */
err:    if ((t_ret =
            __memp_fput(mpf, cp->page, DB_MPOOL_DIRTY)) != 0 && ret == 0)
                ret = t_ret;
        if ((t_ret = __TLPUT(dbc, cp->lock)) != 0 && ret == 0)
                ret = t_ret;
        if (lp != NULL &&
            (t_ret = __memp_fput(mpf, lp, DB_MPOOL_DIRTY)) != 0 && ret == 0)
                ret = t_ret;
        if (rp != NULL &&
            (t_ret = __memp_fput(mpf, rp, DB_MPOOL_DIRTY)) != 0 && ret == 0)
                ret = t_ret;

        return (ret);
}

/*
 * __bam_page --
 *      Split the non-root page of a btree.
 */
static int
__bam_page(dbc, pp, cp)
        DBC *dbc;
        EPG *pp, *cp;
{
        BTREE_CURSOR *bc;
        DBT log_dbt;
        DB_LSN log_lsn;
        DB *dbp;
        DB_LOCK rplock, tplock;
        DB_MPOOLFILE *mpf;
        DB_LSN save_lsn;
        PAGE *lp, *rp, *alloc_rp, *tp;
        db_indx_t split;
        u_int32_t opflags;
        int ret, t_ret;

        dbp = dbc->dbp;
        mpf = dbp->mpf;
        alloc_rp = lp = rp = tp = NULL;
        LOCK_INIT(rplock);
        LOCK_INIT(tplock);
        ret = -1;

        /*
         * Create a new right page for the split, and fill in everything
         * except its LSN and page number.
         *
         * We malloc space for both the left and right pages, so we don't get
         * a new page from the underlying buffer pool until we know the split
         * is going to succeed.  The reason is that we can't release locks
         * acquired during the get-a-new-page process because metadata page
         * locks can't be discarded on failure since we may have modified the
         * free list.  So, if you assume that we're holding a write lock on the
         * leaf page which ran out of space and started this split (e.g., we
         * have already written records to the page, or we retrieved a record
         * from it with the DB_RMW flag set), failing in a split with both a
         * leaf page locked and the metadata page locked can potentially lock
         * up the tree badly, because we've violated the rule of always locking
         * down the tree, and never up.
         */
        if ((ret = __os_malloc(dbp->dbenv, dbp->pgsize, &rp)) != 0)
                goto err;
        P_INIT(rp, dbp->pgsize, 0,
            ISINTERNAL(cp->page) ? PGNO_INVALID : PGNO(cp->page),
            ISINTERNAL(cp->page) ? PGNO_INVALID : NEXT_PGNO(cp->page),
            cp->page->level, TYPE(cp->page));

        /*
         * Create new left page for the split, and fill in everything
         * except its LSN and next-page page number.
         */
        if ((ret = __os_malloc(dbp->dbenv, dbp->pgsize, &lp)) != 0)
                goto err;
        P_INIT(lp, dbp->pgsize, PGNO(cp->page),
            ISINTERNAL(cp->page) ?  PGNO_INVALID : PREV_PGNO(cp->page),
            ISINTERNAL(cp->page) ?  PGNO_INVALID : 0,
            cp->page->level, TYPE(cp->page));

        /*
         * Split right.
         *
         * Only the indices are sorted on the page, i.e., the key/data pairs
         * aren't, so it's simpler to copy the data from the split page onto
         * two new pages instead of copying half the data to a new right page
         * and compacting the left page in place.  Since the left page can't
         * change, we swap the original and the allocated left page after the
         * split.
         */
        if ((ret = __bam_psplit(dbc, cp, lp, rp, &split)) != 0)
                goto err;

        /*
         * Test to see if we are going to be able to insert the new pages into
         * the parent page.  The interesting failure here is that the parent
         * page can't hold the new keys, and has to be split in turn, in which
         * case we want to release all the locks we can.
         */
        if ((ret = __bam_pinsert(dbc, pp, lp, rp, BPI_SPACEONLY)) != 0)
                goto err;

        /*
         * Fix up the previous pointer of any leaf page following the split
         * page.
         *
         * There's interesting deadlock situations here as we try to write-lock
         * a page that's not in our direct ancestry.  Consider a cursor walking
         * backward through the leaf pages, that has our following page locked,
         * and is waiting on a lock for the page we're splitting.  In that case
         * we're going to deadlock here.  It's probably OK, stepping backward
         * through the tree isn't a common operation.
         */
        if (ISLEAF(cp->page) && NEXT_PGNO(cp->page) != PGNO_INVALID) {
                if ((ret = __db_lget(dbc,
                    0, NEXT_PGNO(cp->page), DB_LOCK_WRITE, 0, &tplock)) != 0)
                        goto err;
                if ((ret = __memp_fget(mpf, &NEXT_PGNO(cp->page), 0, &tp)) != 0)
                        goto err;
        }

        /*
         * We've got everything locked down we need, and we know the split
         * is going to succeed.  Go and get the additional page we'll need.
         */
        if ((ret = __db_new(dbc, TYPE(cp->page), &alloc_rp)) != 0)
                goto err;

        /*
         * Lock the new page.  We need to do this for two reasons: first, the
         * fast-lookup code might have a reference to this page in bt_lpgno if
         * the page was recently deleted from the tree, and that code doesn't
         * walk the tree and so won't encounter the parent's page lock.
         * Second, a dirty reader could get to this page via the parent or old
         * page after the split is done but before the transaction is committed
         * or aborted.
         */
        if ((ret = __db_lget(dbc,
            0, PGNO(alloc_rp), DB_LOCK_WRITE, 0, &rplock)) != 0)
                goto err;

        /*
         * Fix up the page numbers we didn't have before.  We have to do this
         * before calling __bam_pinsert because it may copy a page number onto
         * the parent page and it takes the page number from its page argument.
         */
        PGNO(rp) = NEXT_PGNO(lp) = PGNO(alloc_rp);

        /* Actually update the parent page. */
        if ((ret = __bam_pinsert(dbc, pp, lp, rp, 0)) != 0)
                goto err;

        bc = (BTREE_CURSOR *)dbc->internal;
        /* Log the change. */
        if (DBC_LOGGING(dbc)) {
                memset(&log_dbt, 0, sizeof(log_dbt));
                log_dbt.data = cp->page;
                log_dbt.size = dbp->pgsize;
                if (tp == NULL)
                        ZERO_LSN(log_lsn);
                opflags = F_ISSET(bc, C_RECNUM) ? SPL_NRECS : 0;
                if ((ret = __bam_split_log(dbp, dbc->txn, &LSN(cp->page), 0,
                    PGNO(cp->page), &LSN(cp->page), PGNO(alloc_rp),
                    &LSN(alloc_rp), (u_int32_t)NUM_ENT(lp),
                    tp == NULL ? 0 : PGNO(tp),
                    tp == NULL ? &log_lsn : &LSN(tp),
                    PGNO_INVALID, &log_dbt, opflags)) != 0)
                        goto err;

        } else
                LSN_NOT_LOGGED(LSN(cp->page));

        /* Update the LSNs for all involved pages. */
        LSN(alloc_rp) = LSN(cp->page);
        LSN(lp) = LSN(cp->page);
        LSN(rp) = LSN(cp->page);
        if (tp != NULL)
                LSN(tp) = LSN(cp->page);

        /*
         * Copy the left and right pages into place.  There are two paths
         * through here.  Either we are logging and we set the LSNs in the
         * logging path.  However, if we are not logging, then we do not
         * have valid LSNs on lp or rp.  The correct LSNs to use are the
         * ones on the page we got from __db_new or the one that was
         * originally on cp->page.  In both cases, we save the LSN from the
         * real database page (not a malloc'd one) and reapply it after we
         * do the copy.
         */
        save_lsn = alloc_rp->lsn;
        memcpy(alloc_rp, rp, LOFFSET(dbp, rp));
        memcpy((u_int8_t *)alloc_rp + HOFFSET(rp),
            (u_int8_t *)rp + HOFFSET(rp), dbp->pgsize - HOFFSET(rp));
        alloc_rp->lsn = save_lsn;

        save_lsn = cp->page->lsn;
        memcpy(cp->page, lp, LOFFSET(dbp, lp));
        memcpy((u_int8_t *)cp->page + HOFFSET(lp),
            (u_int8_t *)lp + HOFFSET(lp), dbp->pgsize - HOFFSET(lp));
        cp->page->lsn = save_lsn;

        /* Fix up the next-page link. */
        if (tp != NULL)
                PREV_PGNO(tp) = PGNO(rp);

        /* Adjust any cursors. */
        if ((ret = __bam_ca_split(dbc,
            PGNO(cp->page), PGNO(cp->page), PGNO(rp), split, 0)) != 0)
                goto err;

        __os_free(dbp->dbenv, lp);
        __os_free(dbp->dbenv, rp);

        /*
         * Success -- write the real pages back to the store.  As we never
         * acquired any sort of lock on the new page, we release it before
         * releasing locks on the pages that reference it.  We're finished
         * modifying the page so it's not really necessary, but it's neater.
         */
        if ((t_ret =
            __memp_fput(mpf, alloc_rp, DB_MPOOL_DIRTY)) != 0 && ret == 0)
                ret = t_ret;
        if ((t_ret = __TLPUT(dbc, rplock)) != 0 && ret == 0)
                ret = t_ret;
        if ((t_ret =
            __memp_fput(mpf, pp->page, DB_MPOOL_DIRTY)) != 0 && ret == 0)
                ret = t_ret;
        if ((t_ret = __TLPUT(dbc, pp->lock)) != 0 && ret == 0)
                ret = t_ret;
        if ((t_ret =
            __memp_fput(mpf, cp->page, DB_MPOOL_DIRTY)) != 0 && ret == 0)
                ret = t_ret;
        if ((t_ret = __TLPUT(dbc, cp->lock)) != 0 && ret == 0)
                ret = t_ret;
        if (tp != NULL) {
                if ((t_ret =
                    __memp_fput(mpf, tp, DB_MPOOL_DIRTY)) != 0 && ret == 0)
                        ret = t_ret;
                if ((t_ret = __TLPUT(dbc, tplock)) != 0 && ret == 0)
                        ret = t_ret;
        }
        return (ret);

err:    if (lp != NULL)
                __os_free(dbp->dbenv, lp);
        if (rp != NULL)
                __os_free(dbp->dbenv, rp);
        if (alloc_rp != NULL)
                (void)__memp_fput(mpf, alloc_rp, 0);
        if (tp != NULL)
                (void)__memp_fput(mpf, tp, 0);

        /* We never updated the new or next pages, we can release them. */
        (void)__LPUT(dbc, rplock);
        (void)__LPUT(dbc, tplock);

        (void)__memp_fput(mpf, pp->page, 0);
        if (ret == DB_NEEDSPLIT)
                (void)__LPUT(dbc, pp->lock);
        else
                (void)__TLPUT(dbc, pp->lock);

        (void)__memp_fput(mpf, cp->page, 0);
        if (ret == DB_NEEDSPLIT)
                (void)__LPUT(dbc, cp->lock);
        else
                (void)__TLPUT(dbc, cp->lock);

        return (ret);
}

/*
 * __bam_broot --
 *      Fix up the btree root page after it has been split.
 */
static int
__bam_broot(dbc, rootp, lp, rp)
        DBC *dbc;
        PAGE *rootp, *lp, *rp;
{
        BINTERNAL bi, *child_bi;
        BKEYDATA *child_bk;
        BTREE_CURSOR *cp;
        DB *dbp;
        DBT hdr, data;
        db_pgno_t root_pgno;
        int ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;

        /*
         * If the root page was a leaf page, change it into an internal page.
         * We copy the key we split on (but not the key's data, in the case of
         * a leaf page) to the new root page.
         */
        root_pgno = cp->root;
        P_INIT(rootp, dbp->pgsize,
            root_pgno, PGNO_INVALID, PGNO_INVALID, lp->level + 1, P_IBTREE);

        memset(&data, 0, sizeof(data));
        memset(&hdr, 0, sizeof(hdr));

        /*
         * The btree comparison code guarantees that the left-most key on any
         * internal btree page is never used, so it doesn't need to be filled
         * in.  Set the record count if necessary.
         */
        memset(&bi, 0, sizeof(bi));
        bi.len = 0;
        B_TSET(bi.type, B_KEYDATA, 0);
        bi.pgno = lp->pgno;
        if (F_ISSET(cp, C_RECNUM)) {
                bi.nrecs = __bam_total(dbp, lp);
                RE_NREC_SET(rootp, bi.nrecs);
        }
        hdr.data = &bi;
        hdr.size = SSZA(BINTERNAL, data);
        if ((ret =
            __db_pitem(dbc, rootp, 0, BINTERNAL_SIZE(0), &hdr, NULL)) != 0)
                return (ret);

        switch (TYPE(rp)) {
        case P_IBTREE:
                /* Copy the first key of the child page onto the root page. */
                child_bi = GET_BINTERNAL(dbp, rp, 0);

                bi.len = child_bi->len;
                B_TSET(bi.type, child_bi->type, 0);
                bi.pgno = rp->pgno;
                if (F_ISSET(cp, C_RECNUM)) {
                        bi.nrecs = __bam_total(dbp, rp);
                        RE_NREC_ADJ(rootp, bi.nrecs);
                }
                hdr.data = &bi;
                hdr.size = SSZA(BINTERNAL, data);
                data.data = child_bi->data;
                data.size = child_bi->len;
                if ((ret = __db_pitem(dbc, rootp, 1,
                    BINTERNAL_SIZE(child_bi->len), &hdr, &data)) != 0)
                        return (ret);

                /* Increment the overflow ref count. */
                if (B_TYPE(child_bi->type) == B_OVERFLOW)
                        if ((ret = __db_ovref(dbc,
                            ((BOVERFLOW *)(child_bi->data))->pgno, 1)) != 0)
                                return (ret);
                break;
        case P_LDUP:
        case P_LBTREE:
                /* Copy the first key of the child page onto the root page. */
                child_bk = GET_BKEYDATA(dbp, rp, 0);
                switch (B_TYPE(child_bk->type)) {
                case B_KEYDATA:
                        bi.len = child_bk->len;
                        B_TSET(bi.type, child_bk->type, 0);
                        bi.pgno = rp->pgno;
                        if (F_ISSET(cp, C_RECNUM)) {
                                bi.nrecs = __bam_total(dbp, rp);
                                RE_NREC_ADJ(rootp, bi.nrecs);
                        }
                        hdr.data = &bi;
                        hdr.size = SSZA(BINTERNAL, data);
                        data.data = child_bk->data;
                        data.size = child_bk->len;
                        if ((ret = __db_pitem(dbc, rootp, 1,
                            BINTERNAL_SIZE(child_bk->len), &hdr, &data)) != 0)
                                return (ret);
                        break;
                case B_DUPLICATE:
                case B_OVERFLOW:
                        bi.len = BOVERFLOW_SIZE;
                        B_TSET(bi.type, child_bk->type, 0);
                        bi.pgno = rp->pgno;
                        if (F_ISSET(cp, C_RECNUM)) {
                                bi.nrecs = __bam_total(dbp, rp);
                                RE_NREC_ADJ(rootp, bi.nrecs);
                        }
                        hdr.data = &bi;
                        hdr.size = SSZA(BINTERNAL, data);
                        data.data = child_bk;
                        data.size = BOVERFLOW_SIZE;
                        if ((ret = __db_pitem(dbc, rootp, 1,
                            BINTERNAL_SIZE(BOVERFLOW_SIZE), &hdr, &data)) != 0)
                                return (ret);

                        /* Increment the overflow ref count. */
                        if (B_TYPE(child_bk->type) == B_OVERFLOW)
                                if ((ret = __db_ovref(dbc,
                                    ((BOVERFLOW *)child_bk)->pgno, 1)) != 0)
                                        return (ret);
                        break;
                default:
                        return (__db_pgfmt(dbp->dbenv, rp->pgno));
                }
                break;
        default:
                return (__db_pgfmt(dbp->dbenv, rp->pgno));
        }
        return (0);
}

/*
 * __ram_root --
 *      Fix up the recno root page after it has been split.
 */
static int
__ram_root(dbc, rootp, lp, rp)
        DBC *dbc;
        PAGE *rootp, *lp, *rp;
{
        DB *dbp;
        DBT hdr;
        RINTERNAL ri;
        db_pgno_t root_pgno;
        int ret;

        dbp = dbc->dbp;
        root_pgno = dbc->internal->root;

        /* Initialize the page. */
        P_INIT(rootp, dbp->pgsize,
            root_pgno, PGNO_INVALID, PGNO_INVALID, lp->level + 1, P_IRECNO);

        /* Initialize the header. */
        memset(&hdr, 0, sizeof(hdr));
        hdr.data = &ri;
        hdr.size = RINTERNAL_SIZE;

        /* Insert the left and right keys, set the header information. */
        ri.pgno = lp->pgno;
        ri.nrecs = __bam_total(dbp, lp);
        if ((ret = __db_pitem(dbc, rootp, 0, RINTERNAL_SIZE, &hdr, NULL)) != 0)
                return (ret);
        RE_NREC_SET(rootp, ri.nrecs);
        ri.pgno = rp->pgno;
        ri.nrecs = __bam_total(dbp, rp);
        if ((ret = __db_pitem(dbc, rootp, 1, RINTERNAL_SIZE, &hdr, NULL)) != 0)
                return (ret);
        RE_NREC_ADJ(rootp, ri.nrecs);
        return (0);
}

/*
 * __bam_pinsert --
 *      Insert a new key into a parent page, completing the split.
 *
 * PUBLIC: int __bam_pinsert __P((DBC *, EPG *, PAGE *, PAGE *, int));
 */
int
__bam_pinsert(dbc, parent, lchild, rchild, flags)
        DBC *dbc;
        EPG *parent;
        PAGE *lchild, *rchild;
        int flags;
{
        BINTERNAL bi, *child_bi;
        BKEYDATA *child_bk, *tmp_bk;
        BTREE *t;
        BTREE_CURSOR *cp;
        DB *dbp;
        DBT a, b, hdr, data;
        PAGE *ppage;
        RINTERNAL ri;
        db_indx_t off;
        db_recno_t nrecs;
        size_t (*func) __P((DB *, const DBT *, const DBT *));
        u_int32_t n, nbytes, nksize;
        int ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        t = dbp->bt_internal;
        ppage = parent->page;

        /* If handling record numbers, count records split to the right page. */
        nrecs = F_ISSET(cp, C_RECNUM) &&
            !LF_ISSET(BPI_SPACEONLY) ? __bam_total(dbp, rchild) : 0;

        /*
         * Now we insert the new page's first key into the parent page, which
         * completes the split.  The parent points to a PAGE and a page index
         * offset, where the new key goes ONE AFTER the index, because we split
         * to the right.
         *
         * XXX
         * Some btree algorithms replace the key for the old page as well as
         * the new page.  We don't, as there's no reason to believe that the
         * first key on the old page is any better than the key we have, and,
         * in the case of a key being placed at index 0 causing the split, the
         * key is unavailable.
         */
        off = parent->indx + O_INDX;

        /*
         * Calculate the space needed on the parent page.
         *
         * Prefix trees: space hack used when inserting into BINTERNAL pages.
         * Retain only what's needed to distinguish between the new entry and
         * the LAST entry on the page to its left.  If the keys compare equal,
         * retain the entire key.  We ignore overflow keys, and the entire key
         * must be retained for the next-to-leftmost key on the leftmost page
         * of each level, or the search will fail.  Applicable ONLY to internal
         * pages that have leaf pages as children.  Further reduction of the
         * key between pairs of internal pages loses too much information.
         */
        switch (TYPE(rchild)) {
        case P_IBTREE:
                child_bi = GET_BINTERNAL(dbp, rchild, 0);
                nbytes = BINTERNAL_PSIZE(child_bi->len);

                if (P_FREESPACE(dbp, ppage) < nbytes)
                        return (DB_NEEDSPLIT);
                if (LF_ISSET(BPI_SPACEONLY))
                        return (0);

                /* Add a new record for the right page. */
                memset(&bi, 0, sizeof(bi));
                bi.len = child_bi->len;
                B_TSET(bi.type, child_bi->type, 0);
                bi.pgno = rchild->pgno;
                bi.nrecs = nrecs;
                memset(&hdr, 0, sizeof(hdr));
                hdr.data = &bi;
                hdr.size = SSZA(BINTERNAL, data);
                memset(&data, 0, sizeof(data));
                data.data = child_bi->data;
                data.size = child_bi->len;
                if ((ret = __db_pitem(dbc, ppage, off,
                    BINTERNAL_SIZE(child_bi->len), &hdr, &data)) != 0)
                        return (ret);

                /* Increment the overflow ref count. */
                if (B_TYPE(child_bi->type) == B_OVERFLOW)
                        if ((ret = __db_ovref(dbc,
                            ((BOVERFLOW *)(child_bi->data))->pgno, 1)) != 0)
                                return (ret);
                break;
        case P_LDUP:
        case P_LBTREE:
                child_bk = GET_BKEYDATA(dbp, rchild, 0);
                switch (B_TYPE(child_bk->type)) {
                case B_KEYDATA:
                        nbytes = BINTERNAL_PSIZE(child_bk->len);
                        nksize = child_bk->len;

                        /*
                         * Prefix compression:
                         * We set t->bt_prefix to NULL if we have a comparison
                         * callback but no prefix compression callback.  But,
                         * if we're splitting in an off-page duplicates tree,
                         * we still have to do some checking.  If using the
                         * default off-page duplicates comparison routine we
                         * can use the default prefix compression callback. If
                         * not using the default off-page duplicates comparison
                         * routine, we can't do any kind of prefix compression
                         * as there's no way for an application to specify a
                         * prefix compression callback that corresponds to its
                         * comparison callback.
                         *
                         * No prefix compression if we don't have a compression
                         * function, or the key we'd compress isn't a normal
                         * key (for example, it references an overflow page).
                         *
                         * Generate a parent page key for the right child page
                         * from a comparison of the last key on the left child
                         * page and the first key on the right child page.
                         */
                        if (F_ISSET(dbc, DBC_OPD)) {
                                if (dbp->dup_compare == __bam_defcmp)
                                        func = __bam_defpfx;
                                else
                                        func = NULL;
                        } else
                                func = t->bt_prefix;
                        if (func == NULL)
                                goto noprefix;
                        tmp_bk = GET_BKEYDATA(dbp, lchild, NUM_ENT(lchild) -
                            (TYPE(lchild) == P_LDUP ? O_INDX : P_INDX));
                        if (B_TYPE(tmp_bk->type) != B_KEYDATA)
                                goto noprefix;
                        memset(&a, 0, sizeof(a));
                        a.size = tmp_bk->len;
                        a.data = tmp_bk->data;
                        memset(&b, 0, sizeof(b));
                        b.size = child_bk->len;
                        b.data = child_bk->data;
                        nksize = (u_int32_t)func(dbp, &a, &b);
                        if ((n = BINTERNAL_PSIZE(nksize)) < nbytes)
                                nbytes = n;
                        else
                                nksize = child_bk->len;

noprefix:               if (P_FREESPACE(dbp, ppage) < nbytes)
                                return (DB_NEEDSPLIT);
                        if (LF_ISSET(BPI_SPACEONLY))
                                return (0);

                        memset(&bi, 0, sizeof(bi));
                        bi.len = nksize;
                        B_TSET(bi.type, child_bk->type, 0);
                        bi.pgno = rchild->pgno;
                        bi.nrecs = nrecs;
                        memset(&hdr, 0, sizeof(hdr));
                        hdr.data = &bi;
                        hdr.size = SSZA(BINTERNAL, data);
                        memset(&data, 0, sizeof(data));
                        data.data = child_bk->data;
                        data.size = nksize;
                        if ((ret = __db_pitem(dbc, ppage, off,
                            BINTERNAL_SIZE(nksize), &hdr, &data)) != 0)
                                return (ret);
                        break;
                case B_DUPLICATE:
                case B_OVERFLOW:
                        nbytes = BINTERNAL_PSIZE(BOVERFLOW_SIZE);

                        if (P_FREESPACE(dbp, ppage) < nbytes)
                                return (DB_NEEDSPLIT);
                        if (LF_ISSET(BPI_SPACEONLY))
                                return (0);

                        memset(&bi, 0, sizeof(bi));
                        bi.len = BOVERFLOW_SIZE;
                        B_TSET(bi.type, child_bk->type, 0);
                        bi.pgno = rchild->pgno;
                        bi.nrecs = nrecs;
                        memset(&hdr, 0, sizeof(hdr));
                        hdr.data = &bi;
                        hdr.size = SSZA(BINTERNAL, data);
                        memset(&data, 0, sizeof(data));
                        data.data = child_bk;
                        data.size = BOVERFLOW_SIZE;
                        if ((ret = __db_pitem(dbc, ppage, off,
                            BINTERNAL_SIZE(BOVERFLOW_SIZE), &hdr, &data)) != 0)
                                return (ret);

                        /* Increment the overflow ref count. */
                        if (B_TYPE(child_bk->type) == B_OVERFLOW)
                                if ((ret = __db_ovref(dbc,
                                    ((BOVERFLOW *)child_bk)->pgno, 1)) != 0)
                                        return (ret);
                        break;
                default:
                        return (__db_pgfmt(dbp->dbenv, rchild->pgno));
                }
                break;
        case P_IRECNO:
        case P_LRECNO:
                nbytes = RINTERNAL_PSIZE;

                if (P_FREESPACE(dbp, ppage) < nbytes)
                        return (DB_NEEDSPLIT);
                if (LF_ISSET(BPI_SPACEONLY))
                        return (0);

                /* Add a new record for the right page. */
                memset(&hdr, 0, sizeof(hdr));
                hdr.data = &ri;
                hdr.size = RINTERNAL_SIZE;
                ri.pgno = rchild->pgno;
                ri.nrecs = nrecs;
                if ((ret = __db_pitem(dbc,
                    ppage, off, RINTERNAL_SIZE, &hdr, NULL)) != 0)
                        return (ret);
                break;
        default:
                return (__db_pgfmt(dbp->dbenv, rchild->pgno));
        }

        /*
         * If a Recno or Btree with record numbers AM page, or an off-page
         * duplicates tree, adjust the parent page's left page record count.
         */
        if (F_ISSET(cp, C_RECNUM) && !LF_ISSET(BPI_NORECNUM)) {
                /* Log the change. */
                if (DBC_LOGGING(dbc)) {
                        if ((ret = __bam_cadjust_log(dbp, dbc->txn,
                            &LSN(ppage), 0, PGNO(ppage), &LSN(ppage),
                            parent->indx, -(int32_t)nrecs, 0)) != 0)
                                return (ret);
                } else
                        LSN_NOT_LOGGED(LSN(ppage));

                /* Update the left page count. */
                if (dbc->dbtype == DB_RECNO)
                        GET_RINTERNAL(dbp, ppage, parent->indx)->nrecs -= nrecs;
                else
                        GET_BINTERNAL(dbp, ppage, parent->indx)->nrecs -= nrecs;
        }

        return (0);
}

/*
 * __bam_psplit --
 *      Do the real work of splitting the page.
 */
static int
__bam_psplit(dbc, cp, lp, rp, splitret)
        DBC *dbc;
        EPG *cp;
        PAGE *lp, *rp;
        db_indx_t *splitret;
{
        DB *dbp;
        PAGE *pp;
        db_indx_t half, *inp, nbytes, off, splitp, top;
        int adjust, cnt, iflag, isbigkey, ret;

        dbp = dbc->dbp;
        pp = cp->page;
        inp = P_INP(dbp, pp);
        adjust = TYPE(pp) == P_LBTREE ? P_INDX : O_INDX;

        /*
         * If we're splitting the first (last) page on a level because we're
         * inserting (appending) a key to it, it's likely that the data is
         * sorted.  Moving a single item to the new page is less work and can
         * push the fill factor higher than normal.  This is trivial when we
         * are splitting a new page before the beginning of the tree, all of
         * the interesting tests are against values of 0.
         *
         * Catching appends to the tree is harder.  In a simple append, we're
         * inserting an item that sorts past the end of the tree; the cursor
         * will point past the last element on the page.  But, in trees with
         * duplicates, the cursor may point to the last entry on the page --
         * in this case, the entry will also be the last element of a duplicate
         * set (the last because the search call specified the S_DUPLAST flag).
         * The only way to differentiate between an insert immediately before
         * the last item in a tree or an append after a duplicate set which is
         * also the last item in the tree is to call the comparison function.
         * When splitting internal pages during an append, the search code
         * guarantees the cursor always points to the largest page item less
         * than the new internal entry.  To summarize, we want to catch three
         * possible index values:
         *
         *      NUM_ENT(page)           Btree/Recno leaf insert past end-of-tree
         *      NUM_ENT(page) - O_INDX  Btree or Recno internal insert past EOT
         *      NUM_ENT(page) - P_INDX  Btree leaf insert past EOT after a set
         *                                  of duplicates
         *
         * two of which, (NUM_ENT(page) - O_INDX or P_INDX) might be an insert
         * near the end of the tree, and not after the end of the tree at all.
         * Do a simple test which might be wrong because calling the comparison
         * functions is expensive.  Regardless, it's not a big deal if we're
         * wrong, we'll do the split the right way next time.
         */
        off = 0;
        if (NEXT_PGNO(pp) == PGNO_INVALID && cp->indx >= NUM_ENT(pp) - adjust)
                off = NUM_ENT(pp) - adjust;
        else if (PREV_PGNO(pp) == PGNO_INVALID && cp->indx == 0)
                off = adjust;
        if (off != 0)
                goto sort;

        /*
         * Split the data to the left and right pages.  Try not to split on
         * an overflow key.  (Overflow keys on internal pages will slow down
         * searches.)  Refuse to split in the middle of a set of duplicates.
         *
         * First, find the optimum place to split.
         *
         * It's possible to try and split past the last record on the page if
         * there's a very large record at the end of the page.  Make sure this
         * doesn't happen by bounding the check at the next-to-last entry on
         * the page.
         *
         * Note, we try and split half the data present on the page.  This is
         * because another process may have already split the page and left
         * it half empty.  We don't try and skip the split -- we don't know
         * how much space we're going to need on the page, and we may need up
         * to half the page for a big item, so there's no easy test to decide
         * if we need to split or not.  Besides, if two threads are inserting
         * data into the same place in the database, we're probably going to
         * need more space soon anyway.
         */
        top = NUM_ENT(pp) - adjust;
        half = (dbp->pgsize - HOFFSET(pp)) / 2;
        for (nbytes = 0, off = 0; off < top && nbytes < half; ++off)
                switch (TYPE(pp)) {
                case P_IBTREE:
                        if (B_TYPE(
                            GET_BINTERNAL(dbp, pp, off)->type) == B_KEYDATA)
                                nbytes += BINTERNAL_SIZE(
                                   GET_BINTERNAL(dbp, pp, off)->len);
                        else
                                nbytes += BINTERNAL_SIZE(BOVERFLOW_SIZE);
                        break;
                case P_LBTREE:
                        if (B_TYPE(GET_BKEYDATA(dbp, pp, off)->type) ==
                            B_KEYDATA)
                                nbytes += BKEYDATA_SIZE(GET_BKEYDATA(dbp,
                                    pp, off)->len);
                        else
                                nbytes += BOVERFLOW_SIZE;

                        ++off;
                        /* FALLTHROUGH */
                case P_LDUP:
                case P_LRECNO:
                        if (B_TYPE(GET_BKEYDATA(dbp, pp, off)->type) ==
                            B_KEYDATA)
                                nbytes += BKEYDATA_SIZE(GET_BKEYDATA(dbp,
                                    pp, off)->len);
                        else
                                nbytes += BOVERFLOW_SIZE;
                        break;
                case P_IRECNO:
                        nbytes += RINTERNAL_SIZE;
                        break;
                default:
                        return (__db_pgfmt(dbp->dbenv, pp->pgno));
                }
sort:   splitp = off;

        /*
         * Splitp is either at or just past the optimum split point.  If the
         * tree type is such that we're going to promote a key to an internal
         * page, and our current choice is an overflow key, look for something
         * close by that's smaller.
         */
        switch (TYPE(pp)) {
        case P_IBTREE:
                iflag = 1;
                isbigkey =
                    B_TYPE(GET_BINTERNAL(dbp, pp, off)->type) != B_KEYDATA;
                break;
        case P_LBTREE:
        case P_LDUP:
                iflag = 0;
                isbigkey = B_TYPE(GET_BKEYDATA(dbp, pp, off)->type) !=
                    B_KEYDATA;
                break;
        default:
                iflag = isbigkey = 0;
        }
        if (isbigkey)
                for (cnt = 1; cnt <= 3; ++cnt) {
                        off = splitp + cnt * adjust;
                        if (off < (db_indx_t)NUM_ENT(pp) &&
                            ((iflag && B_TYPE(
                            GET_BINTERNAL(dbp, pp,off)->type) == B_KEYDATA) ||
                            B_TYPE(GET_BKEYDATA(dbp, pp, off)->type) ==
                            B_KEYDATA)) {
                                splitp = off;
                                break;
                        }
                        if (splitp <= (db_indx_t)(cnt * adjust))
                                continue;
                        off = splitp - cnt * adjust;
                        if (iflag ? B_TYPE(
                            GET_BINTERNAL(dbp, pp, off)->type) == B_KEYDATA :
                            B_TYPE(GET_BKEYDATA(dbp, pp, off)->type) ==
                            B_KEYDATA) {
                                splitp = off;
                                break;
                        }
                }

        /*
         * We can't split in the middle a set of duplicates.  We know that
         * no duplicate set can take up more than about 25% of the page,
         * because that's the point where we push it off onto a duplicate
         * page set.  So, this loop can't be unbounded.
         */
        if (TYPE(pp) == P_LBTREE &&
            inp[splitp] == inp[splitp - adjust])
                for (cnt = 1;; ++cnt) {
                        off = splitp + cnt * adjust;
                        if (off < NUM_ENT(pp) &&
                            inp[splitp] != inp[off]) {
                                splitp = off;
                                break;
                        }
                        if (splitp <= (db_indx_t)(cnt * adjust))
                                continue;
                        off = splitp - cnt * adjust;
                        if (inp[splitp] != inp[off]) {
                                splitp = off + adjust;
                                break;
                        }
                }

        /* We're going to split at splitp. */
        if ((ret = __bam_copy(dbp, pp, lp, 0, splitp)) != 0)
                return (ret);
        if ((ret = __bam_copy(dbp, pp, rp, splitp, NUM_ENT(pp))) != 0)
                return (ret);

        *splitret = splitp;
        return (0);
}

/*
 * __bam_copy --
 *      Copy a set of records from one page to another.
 *
 * PUBLIC: int __bam_copy __P((DB *, PAGE *, PAGE *, u_int32_t, u_int32_t));
 */
int
__bam_copy(dbp, pp, cp, nxt, stop)
        DB *dbp;
        PAGE *pp, *cp;
        u_int32_t nxt, stop;
{
        db_indx_t *cinp, nbytes, off, *pinp;

        cinp = P_INP(dbp, cp);
        pinp = P_INP(dbp, pp);
        /*
         * Nxt is the offset of the next record to be placed on the target page.
         */
        for (off = 0; nxt < stop; ++nxt, ++NUM_ENT(cp), ++off) {
                switch (TYPE(pp)) {
                case P_IBTREE:
                        if (B_TYPE(
                            GET_BINTERNAL(dbp, pp, nxt)->type) == B_KEYDATA)
                                nbytes = BINTERNAL_SIZE(
                                    GET_BINTERNAL(dbp, pp, nxt)->len);
                        else
                                nbytes = BINTERNAL_SIZE(BOVERFLOW_SIZE);
                        break;
                case P_LBTREE:
                        /*
                         * If we're on a key and it's a duplicate, just copy
                         * the offset.
                         */
                        if (off != 0 && (nxt % P_INDX) == 0 &&
                            pinp[nxt] == pinp[nxt - P_INDX]) {
                                cinp[off] = cinp[off - P_INDX];
                                continue;
                        }
                        /* FALLTHROUGH */
                case P_LDUP:
                case P_LRECNO:
                        if (B_TYPE(GET_BKEYDATA(dbp, pp, nxt)->type) ==
                            B_KEYDATA)
                                nbytes = BKEYDATA_SIZE(GET_BKEYDATA(dbp,
                                    pp, nxt)->len);
                        else
                                nbytes = BOVERFLOW_SIZE;
                        break;
                case P_IRECNO:
                        nbytes = RINTERNAL_SIZE;
                        break;
                default:
                        return (__db_pgfmt(dbp->dbenv, pp->pgno));
                }
                cinp[off] = HOFFSET(cp) -= nbytes;
                memcpy(P_ENTRY(dbp, cp, off), P_ENTRY(dbp, pp, nxt), nbytes);
        }
        return (0);
}

---