source: trunk/third/db/btree/bt_cursor.c @ 17055

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998, 1999, 2000
 *      Sleepycat Software.  All rights reserved.
 */

#include "db_config.h"

#ifndef lint
static const char revid[] = "$Id: bt_cursor.c,v 1.1.1.2 2002-02-11 16:30:10 ghudson Exp $";
#endif /* not lint */

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

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

#include "db_int.h"
#include "db_page.h"
#include "db_shash.h"
#include "btree.h"
#include "lock.h"
#include "qam.h"
#include "common_ext.h"

static int  __bam_c_close __P((DBC *, db_pgno_t, int *));
static int  __bam_c_del __P((DBC *));
static int  __bam_c_destroy __P((DBC *));
static int  __bam_c_first __P((DBC *));
static int  __bam_c_get __P((DBC *, DBT *, DBT *, u_int32_t, db_pgno_t *));
static int  __bam_c_getstack __P((DBC *));
static int  __bam_c_last __P((DBC *));
static int  __bam_c_next __P((DBC *, int));
static int  __bam_c_physdel __P((DBC *));
static int  __bam_c_prev __P((DBC *));
static int  __bam_c_put __P((DBC *, DBT *, DBT *, u_int32_t, db_pgno_t *));
static void __bam_c_reset __P((BTREE_CURSOR *));
static int  __bam_c_search __P((DBC *, const DBT *, u_int32_t, int *));
static int  __bam_c_writelock __P((DBC *));
static int  __bam_getboth_finddatum __P((DBC *, DBT *));
static int  __bam_getbothc __P((DBC *, DBT *));
static int  __bam_isopd __P((DBC *, db_pgno_t *));

/*
 * Acquire a new page/lock.  If we hold a page/lock, discard the page, and
 * lock-couple the lock.
 *
 * !!!
 * We have to handle both where we have a lock to lock-couple and where we
 * don't -- we don't duplicate locks when we duplicate cursors if we are
 * running in a transaction environment as there's no point if locks are
 * never discarded.  This means that the cursor may or may not hold a lock.
 */
#undef  ACQUIRE
#define ACQUIRE(dbc, mode, lpgno, lock, fpgno, pagep, ret) {\
        if ((pagep) != NULL) {                                          \
                ret = memp_fput((dbc)->dbp->mpf, pagep, 0);             \
                pagep = NULL;                                           \
        } else                                                          \
                ret = 0;                                                \
        if ((ret) == 0 && STD_LOCKING(dbc))                             \
                ret = __db_lget(dbc,                                    \
                    (lock).off == LOCK_INVALID ? 0 : LCK_COUPLE,        \
                    lpgno, mode, 0, &lock);                             \
        else                                                            \
                (lock).off = LOCK_INVALID;                              \
        if ((ret) == 0)                                                 \
                ret = memp_fget((dbc)->dbp->mpf, &(fpgno), 0, &(pagep));\
}

/* Acquire a new page/lock for a cursor. */
#undef  ACQUIRE_CUR
#define ACQUIRE_CUR(dbc, mode, ret) {                                   \
        BTREE_CURSOR *__cp = (BTREE_CURSOR *)(dbc)->internal;           \
        ACQUIRE(dbc, mode,                                              \
            __cp->pgno, __cp->lock, __cp->pgno, __cp->page, ret);       \
        if ((ret) == 0)                                                 \
                __cp->lock_mode = (mode);                               \
}

/*
 * Acquire a new page/lock for a cursor, and move the cursor on success.
 * The reason that this is a separate macro is because we don't want to
 * set the pgno/indx fields in the cursor until we actually have the lock,
 * otherwise the cursor adjust routines will adjust the cursor even though
 * we're not really on the page.
 */
#undef  ACQUIRE_CUR_SET
#define ACQUIRE_CUR_SET(dbc, mode, p, ret) {                            \
        BTREE_CURSOR *__cp = (BTREE_CURSOR *)(dbc)->internal;           \
        ACQUIRE(dbc, mode, p, __cp->lock, p, __cp->page, ret);          \
        if ((ret) == 0) {                                               \
                __cp->pgno = p;                                 \
                __cp->indx = 0;                                 \
                __cp->lock_mode = (mode);                               \
        }                                                               \
}

/*
 * Acquire a write lock if we don't already have one.
 *
 * !!!
 * See ACQUIRE macro on why we handle cursors that don't have locks.
 */
#undef  ACQUIRE_WRITE_LOCK
#define ACQUIRE_WRITE_LOCK(dbc, ret) {                                  \
        BTREE_CURSOR *__cp = (BTREE_CURSOR *)(dbc)->internal;           \
        ret = 0;                                                        \
        if (STD_LOCKING(dbc) &&                                         \
            __cp->lock_mode != DB_LOCK_WRITE &&                         \
            ((ret) = __db_lget(dbc,                                     \
            __cp->lock.off == LOCK_INVALID ? 0 : LCK_COUPLE,            \
            __cp->pgno, DB_LOCK_WRITE, 0, &__cp->lock)) == 0)           \
                __cp->lock_mode = DB_LOCK_WRITE;                        \
}

/* Discard the current page/lock. */
#undef  DISCARD
#define DISCARD(dbc, ldiscard, lock, pagep, ret) {                      \
        int __t_ret;                                                    \
        if ((pagep) != NULL) {                                          \
                ret = memp_fput((dbc)->dbp->mpf, pagep, 0);             \
                pagep = NULL;                                           \
        } else                                                          \
                ret = 0;                                                \
        if ((lock).off != LOCK_INVALID) {                               \
                __t_ret = ldiscard ?                                    \
                    __LPUT((dbc), lock): __TLPUT((dbc), lock);          \
                if (__t_ret != 0 && (ret) == 0)                         \
                        ret = __t_ret;                                  \
                (lock).off = LOCK_INVALID;                              \
        }                                                               \
}

/* Discard the current page/lock for a cursor. */
#undef  DISCARD_CUR
#define DISCARD_CUR(dbc, ret) {                                         \
        BTREE_CURSOR *__cp = (BTREE_CURSOR *)(dbc)->internal;           \
        DISCARD(dbc, 0, __cp->lock, __cp->page, ret);                   \
        if ((ret) == 0)                                                 \
                __cp->lock_mode = DB_LOCK_NG;                           \
}

/* If on-page item is a deleted record. */
#undef  IS_DELETED
#define IS_DELETED(page, indx)                                          \
        B_DISSET(GET_BKEYDATA(page,                                     \
            (indx) + (TYPE(page) == P_LBTREE ? O_INDX : 0))->type)
#undef  IS_CUR_DELETED
#define IS_CUR_DELETED(dbc)                                             \
        IS_DELETED((dbc)->internal->page, (dbc)->internal->indx)

/*
 * Test to see if two cursors could point to duplicates of the same key.
 * In the case of off-page duplicates they are they same, as the cursors
 * will be in the same off-page duplicate tree.  In the case of on-page
 * duplicates, the key index offsets must be the same.  For the last test,
 * as the original cursor may not have a valid page pointer, we use the
 * current cursor's.
 */
#undef  IS_DUPLICATE
#define IS_DUPLICATE(dbc, i1, i2)                                       \
            (((PAGE *)(dbc)->internal->page)->inp[i1] ==                \
             ((PAGE *)(dbc)->internal->page)->inp[i2])
#undef  IS_CUR_DUPLICATE
#define IS_CUR_DUPLICATE(dbc, orig_pgno, orig_indx)                     \
        (F_ISSET(dbc, DBC_OPD) ||                                       \
            (orig_pgno == (dbc)->internal->pgno &&                      \
            IS_DUPLICATE(dbc, (dbc)->internal->indx, orig_indx)))

/*
 * __bam_c_reset --
 *      Initialize internal cursor structure.
 */
static void
__bam_c_reset(cp)
        BTREE_CURSOR *cp;
{
        cp->csp = cp->sp;
        cp->lock.off = LOCK_INVALID;
        cp->lock_mode = DB_LOCK_NG;
        cp->recno = RECNO_OOB;
        cp->flags = 0;
}

/*
 * __bam_c_init --
 *      Initialize the access private portion of a cursor
 *
 * PUBLIC: int __bam_c_init __P((DBC *, DBTYPE));
 */
int
__bam_c_init(dbc, dbtype)
        DBC *dbc;
        DBTYPE dbtype;
{
        BTREE *t;
        BTREE_CURSOR *cp;
        DB *dbp;
        u_int32_t minkey;
        int ret;

        dbp = dbc->dbp;

        /* Allocate/initialize the internal structure. */
        if (dbc->internal == NULL) {
                if ((ret = __os_malloc(dbp->dbenv,
                    sizeof(BTREE_CURSOR), NULL, &cp)) != 0)
                        return (ret);
                dbc->internal = (DBC_INTERNAL *)cp;

                cp->sp = cp->csp = cp->stack;
                cp->esp = cp->stack + sizeof(cp->stack) / sizeof(cp->stack[0]);
        } else
                cp = (BTREE_CURSOR *)dbc->internal;
        __bam_c_reset(cp);

        /* Initialize methods. */
        dbc->c_close = __db_c_close;
        dbc->c_count = __db_c_count;
        dbc->c_del = __db_c_del;
        dbc->c_dup = __db_c_dup;
        dbc->c_get = __db_c_get;
        dbc->c_put = __db_c_put;
        if (dbtype == DB_BTREE) {
                dbc->c_am_close = __bam_c_close;
                dbc->c_am_del = __bam_c_del;
                dbc->c_am_destroy = __bam_c_destroy;
                dbc->c_am_get = __bam_c_get;
                dbc->c_am_put = __bam_c_put;
                dbc->c_am_writelock = __bam_c_writelock;
        } else {
                dbc->c_am_close = __bam_c_close;
                dbc->c_am_del = __ram_c_del;
                dbc->c_am_destroy = __bam_c_destroy;
                dbc->c_am_get = __ram_c_get;
                dbc->c_am_put = __ram_c_put;
                dbc->c_am_writelock = __bam_c_writelock;
        }

        /*
         * The btree leaf page data structures require that two key/data pairs
         * (or four items) fit on a page, but other than that there's no fixed
         * requirement.  The btree off-page duplicates only require two items,
         * to be exact, but requiring four for them as well seems reasonable.
         *
         * Recno uses the btree bt_ovflsize value -- it's close enough.
         */
        t = dbp->bt_internal;
        minkey = F_ISSET(dbc, DBC_OPD) ? 2 : t->bt_minkey;
        cp->ovflsize = B_MINKEY_TO_OVFLSIZE(minkey, dbp->pgsize);

        return (0);
}

/*
 * __bam_c_refresh
 *      Set things up properly for cursor re-use.
 *
 * PUBLIC: int __bam_c_refresh __P((DBC *));
 */
int
__bam_c_refresh(dbc)
        DBC *dbc;
{
        BTREE_CURSOR *cp;
        DB *dbp;

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

        /*
         * If our caller set the root page number, it's because the root was
         * known.  This is always the case for off page dup cursors.  Else,
         * pull it out of our internal information.
         */
        if (cp->root == PGNO_INVALID)
                cp->root = ((BTREE *)dbp->bt_internal)->bt_root;

        /* Initialize for record numbers. */
        if (F_ISSET(dbc, DBC_OPD) ||
            dbc->dbtype == DB_RECNO || F_ISSET(dbp, DB_BT_RECNUM)) {
                F_SET(cp, C_RECNUM);

                /*
                 * All btrees that support record numbers, optionally standard
                 * recno trees, and all off-page duplicate recno trees have
                 * mutable record numbers.
                 */
                if ((F_ISSET(dbc, DBC_OPD) && dbc->dbtype == DB_RECNO) ||
                    F_ISSET(dbp, DB_BT_RECNUM | DB_RE_RENUMBER))
                        F_SET(cp, C_RENUMBER);
        }

        return (0);
}

/*
 * __bam_c_close --
 *      Close down the cursor.
 */
static int
__bam_c_close(dbc, root_pgno, rmroot)
        DBC *dbc;
        db_pgno_t root_pgno;
        int *rmroot;
{
        BTREE_CURSOR *cp, *cp_opd, *cp_c;
        DB *dbp;
        DBC *dbc_opd, *dbc_c;
        PAGE *h;
        u_int32_t num;
        int cdb_lock, ret, t_ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        cp_opd = (dbc_opd = cp->opd) == NULL ?
            NULL : (BTREE_CURSOR *)dbc_opd->internal;
        cdb_lock = ret = 0;

        /*
         * There are 3 ways this function is called:
         *
         * 1. Closing a primary cursor: we get called with a pointer to a
         *    primary cursor that has a NULL opd field.  This happens when
         *    closing a btree/recno database cursor without an associated
         *    off-page duplicate tree.
         *
         * 2. Closing a primary and an off-page duplicate cursor stack: we
         *    get called with a pointer to the primary cursor which has a
         *    non-NULL opd field.  This happens when closing a btree cursor
         *    into database with an associated off-page btree/recno duplicate
         *    tree. (It can't be a primary recno database, recno databases
         *    don't support duplicates.)
         *
         * 3. Closing an off-page duplicate cursor stack: we get called with
         *    a pointer to the off-page duplicate cursor.  This happens when
         *    closing a non-btree database that has an associated off-page
         *    btree/recno duplicate tree or for a btree database when the
         *    opd tree is not empty (root_pgno == PGNO_INVALID).
         *
         * If either the primary or off-page duplicate cursor deleted a btree
         * key/data pair, check to see if the item is still referenced by a
         * different cursor.  If it is, confirm that cursor's delete flag is
         * set and leave it to that cursor to do the delete.
         *
         * NB: The test for == 0 below is correct.  Our caller already removed
         * our cursor argument from the active queue, we won't find it when we
         * search the queue in __bam_ca_delete().
         * NB: It can't be true that both the primary and off-page duplicate
         * cursors have deleted a btree key/data pair.  Either the primary
         * cursor may have deleted an item and there's no off-page duplicate
         * cursor, or there's an off-page duplicate cursor and it may have
         * deleted an item.
         *
         * Primary recno databases aren't an issue here.  Recno keys are either
         * deleted immediately or never deleted, and do not have to be handled
         * here.
         *
         * Off-page duplicate recno databases are an issue here, cases #2 and
         * #3 above can both be off-page recno databases.  The problem is the
         * same as the final problem for off-page duplicate btree databases.
         * If we no longer need the off-page duplicate tree, we want to remove
         * it.  For off-page duplicate btrees, we are done with the tree when
         * we delete the last item it contains, i.e., there can be no further
         * references to it when it's empty.  For off-page duplicate recnos,
         * we remove items from the tree as the application calls the remove
         * function, so we are done with the tree when we close the last cursor
         * that references it.
         *
         * We optionally take the root page number from our caller.  If the
         * primary database is a btree, we can get it ourselves because dbc
         * is the primary cursor.  If the primary database is not a btree,
         * the problem is that we may be dealing with a stack of pages.  The
         * cursor we're using to do the delete points at the bottom of that
         * stack and we need the top of the stack.
         */
        if (F_ISSET(cp, C_DELETED)) {
                dbc_c = dbc;
                switch (dbc->dbtype) {
                case DB_BTREE:                          /* Case #1, #3. */
                        if (__bam_ca_delete(dbp, cp->pgno, cp->indx, 1) == 0)
                                goto lock;
                        goto done;
                case DB_RECNO:
                        if (!F_ISSET(dbc, DBC_OPD))     /* Case #1. */
                                goto done;
                                                        /* Case #3. */
                        if (__ram_ca_delete(dbp, cp->root) == 0)
                                goto lock;
                        goto done;
                default:
                        return (__db_unknown_type(dbp->dbenv,
                                "__bam_c_close", dbc->dbtype));
                }
        }

        if (dbc_opd == NULL)
                goto done;

        if (F_ISSET(cp_opd, C_DELETED)) {               /* Case #2. */
                /*
                 * We will not have been provided a root page number.  Acquire
                 * one from the primary database.
                 */
                if ((ret = memp_fget(dbp->mpf, &cp->pgno, 0, &h)) != 0)
                        goto err;
                root_pgno = GET_BOVERFLOW(h, cp->indx + O_INDX)->pgno;
                if ((ret = memp_fput(dbp->mpf, h, 0)) != 0)
                        goto err;

                dbc_c = dbc_opd;
                switch (dbc_opd->dbtype) {
                case DB_BTREE:
                        if (__bam_ca_delete(
                            dbp, cp_opd->pgno, cp_opd->indx, 1) == 0)
                                goto lock;
                        goto done;
                case DB_RECNO:
                        if (__ram_ca_delete(dbp, cp_opd->root) == 0)
                                goto lock;
                        goto done;
                default:
                        return (__db_unknown_type(dbp->dbenv,
                                "__bam_c_close", dbc->dbtype));
                }
        }
        goto done;

lock:   cp_c = (BTREE_CURSOR *)dbc_c->internal;

        /*
         * If this is CDB, upgrade the lock if necessary.  While we acquired
         * the write lock to logically delete the record, we released it when
         * we returned from that call, and so may not be holding a write lock
         * at the moment.  NB: to get here in CDB we must either be holding a
         * write lock or be the only cursor that is permitted to acquire write
         * locks.  The reason is that there can never be more than a single CDB
         * write cursor (that cursor cannot be dup'd), and so that cursor must
         * be closed and the item therefore deleted before any other cursor
         * could acquire a reference to this item.
         *
         * Note that dbc may be an off-page dup cursor;  this is the sole
         * instance in which an OPD cursor does any locking, but it's necessary
         * because we may be closed by ourselves without a parent cursor
         * handy, and we have to do a lock upgrade on behalf of somebody.
         * If this is the case, the OPD has been given the parent's locking
         * info in __db_c_get--the OPD is also a WRITEDUP.
         */
        if (CDB_LOCKING(dbp->dbenv)) {
                DB_ASSERT(!F_ISSET(dbc, DBC_OPD) || F_ISSET(dbc, DBC_WRITEDUP));
                if (!F_ISSET(dbc, DBC_WRITER)) {
                        if ((ret =
                            lock_get(dbp->dbenv, dbc->locker, DB_LOCK_UPGRADE,
                            &dbc->lock_dbt, DB_LOCK_WRITE, &dbc->mylock)) != 0)
                                goto err;
                        cdb_lock = 1;
                }

                cp_c->lock.off = LOCK_INVALID;
                if ((ret =
                    memp_fget(dbp->mpf, &cp_c->pgno, 0, &cp_c->page)) != 0)
                        goto err;

                goto delete;
        }

        /*
         * The variable dbc_c has been initialized to reference the cursor in
         * which we're going to do the delete.  Initialize the cursor's page
         * and lock structures as necessary.
         *
         * First, we may not need to acquire any locks.  If we're in case #3,
         * that is, the primary database isn't a btree database, our caller
         * is responsible for acquiring any necessary locks before calling us.
         */
        if (F_ISSET(dbc, DBC_OPD)) {
                cp_c->lock.off = LOCK_INVALID;
                if ((ret =
                    memp_fget(dbp->mpf, &cp_c->pgno, 0, &cp_c->page)) != 0)
                        goto err;
                goto delete;
        }

        /*
         * Otherwise, acquire a write lock.  If the cursor that did the initial
         * logical deletion (and which had a write lock) is not the same as the
         * cursor doing the physical deletion (which may have only ever had a
         * read lock on the item), we need to upgrade.  The confusion comes as
         * follows:
         *
         *      C1      created, acquires item read lock
         *      C2      dup C1, create C2, also has item read lock.
         *      C1      acquire write lock, delete item
         *      C1      close
         *      C2      close, needs a write lock to physically delete item.
         *
         * If we're in a TXN, we know that C2 will be able to acquire the write
         * lock, because no locker other than the one shared by C1 and C2 can
         * acquire a write lock -- the original write lock C1 acquire was never
         * discarded.
         *
         * If we're not in a TXN, it's nastier.  Other cursors might acquire
         * read locks on the item after C1 closed, discarding its write lock,
         * and such locks would prevent C2 from acquiring a read lock.  That's
         * OK, though, we'll simply wait until we can acquire a read lock, or
         * we'll deadlock.  (Which better not happen, since we're not in a TXN.)
         *
         * Lock the primary database page, regardless of whether we're deleting
         * an item on a primary database page or an off-page duplicates page.
         */
        ACQUIRE(dbc, DB_LOCK_WRITE,
            cp->pgno, cp_c->lock, cp_c->pgno, cp_c->page, ret);
        if (ret != 0)
                goto err;

delete: /*
         * If the delete occurred in a btree, delete the on-page physical item
         * referenced by the cursor.
         */
        if (dbc_c->dbtype == DB_BTREE && (ret = __bam_c_physdel(dbc_c)) != 0)
                goto err;

        /*
         * If we're not working in an off-page duplicate tree, then we're
         * done.
         */
        if (!F_ISSET(dbc_c, DBC_OPD) || root_pgno == PGNO_INVALID)
                goto done;

        /*
         * We may have just deleted the last element in the off-page duplicate
         * tree, and closed the last cursor in the tree.  For an off-page btree
         * there are no other cursors in the tree by definition, if the tree is
         * empty.  For an off-page recno we know we have closed the last cursor
         * in the tree because the __ram_ca_delete call above returned 0 only
         * in that case.  So, if the off-page duplicate tree is empty at this
         * point, we want to remove it.
         */
        if ((ret = memp_fget(dbp->mpf, &root_pgno, 0, &h)) != 0)
                goto err;
        if ((num = NUM_ENT(h)) == 0) {
                if ((ret = __db_free(dbc, h)) != 0)
                        goto err;
        } else {
                if ((ret = memp_fput(dbp->mpf, h, 0)) != 0)
                        goto err;
                goto done;
        }

        /*
         * When removing the tree, we have to do one of two things.  If this is
         * case #2, that is, the primary tree is a btree, delete the key that's
         * associated with the tree from the btree leaf page.  We know we are
         * the only reference to it and we already have the correct lock.  We
         * detect this case because the cursor that was passed to us references
         * an off-page duplicate cursor.
         *
         * If this is case #3, that is, the primary tree isn't a btree, pass
         * the information back to our caller, it's their job to do cleanup on
         * the primary page.
         */
        if (dbc_opd != NULL) {
                cp->lock.off = LOCK_INVALID;
                if ((ret = memp_fget(dbp->mpf, &cp->pgno, 0, &cp->page)) != 0)
                        goto err;
                if ((ret = __bam_c_physdel(dbc)) != 0)
                        goto err;
        } else
                *rmroot = 1;
err:
done:   /*
         * Discard the page references and locks, and confirm that the stack
         * has been emptied.
         */
        if (dbc_opd != NULL) {
                DISCARD_CUR(dbc_opd, t_ret);
                if (t_ret != 0 && ret == 0)
                        ret = t_ret;
        }
        DISCARD_CUR(dbc, t_ret);
        if (t_ret != 0 && ret == 0)
                ret = t_ret;

        /* Downgrade any CDB lock we acquired. */
        if (cdb_lock)
                (void)__lock_downgrade(
                    dbp->dbenv, &dbc->mylock, DB_LOCK_IWRITE, 0);

        return (ret);
}

/*
 * __bam_c_destroy --
 *      Close a single cursor -- internal version.
 */
static int
__bam_c_destroy(dbc)
        DBC *dbc;
{
        /* Discard the structures. */
        __os_free(dbc->internal, sizeof(BTREE_CURSOR));

        return (0);
}

/*
 * __bam_c_count --
 *      Return a count of on and off-page duplicates.
 *
 * PUBLIC: int __bam_c_count __P((DBC *, db_recno_t *));
 */
int
__bam_c_count(dbc, recnop)
        DBC *dbc;
        db_recno_t *recnop;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        db_indx_t indx, top;
        db_recno_t recno;
        int ret;

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

        /*
         * Called with the top-level cursor that may reference an off-page
         * duplicates page.  If it's a set of on-page duplicates, get the
         * page and count.  Otherwise, get the root page of the off-page
         * duplicate tree, and use the count.  We don't have to acquire any
         * new locks, we have to have a read lock to even get here.
         */
        if (cp->opd == NULL) {
                if ((ret = memp_fget(dbp->mpf, &cp->pgno, 0, &cp->page)) != 0)
                        return (ret);

                /*
                 * Move back to the beginning of the set of duplicates and
                 * then count forward.
                 */
                for (indx = cp->indx;; indx -= P_INDX)
                        if (indx == 0 ||
                            !IS_DUPLICATE(dbc, indx, indx - P_INDX))
                                break;
                for (recno = 1, top = NUM_ENT(cp->page) - P_INDX;
                    indx < top; ++recno, indx += P_INDX)
                        if (!IS_DUPLICATE(dbc, indx, indx + P_INDX))
                                break;
                *recnop = recno;
        } else {
                if ((ret = memp_fget(dbp->mpf,
                    &cp->opd->internal->root, 0, &cp->page)) != 0)
                        return (ret);

                *recnop = RE_NREC(cp->page);
        }

        ret = memp_fput(dbp->mpf, cp->page, 0);
        cp->page = NULL;

        return (ret);
}

/*
 * __bam_c_del --
 *      Delete using a cursor.
 */
static int
__bam_c_del(dbc)
        DBC *dbc;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        int ret, t_ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        ret = 0;

        /* If the item was already deleted, return failure. */
        if (F_ISSET(cp, C_DELETED))
                return (DB_KEYEMPTY);

        /*
         * We don't physically delete the record until the cursor moves, so
         * we have to have a long-lived write lock on the page instead of a
         * a long-lived read lock.  Note, we have to have a read lock to even
         * get here.
         *
         * If we're maintaining record numbers, we lock the entire tree, else
         * we lock the single page.
         */
        if (F_ISSET(cp, C_RECNUM)) {
                if ((ret = __bam_c_getstack(dbc)) != 0)
                        goto err;
        } else {
                ACQUIRE_CUR(dbc, DB_LOCK_WRITE, ret);
                if (ret != 0)
                        goto err;
        }

        /* Log the change. */
        if (DB_LOGGING(dbc) &&
            (ret = __bam_cdel_log(dbp->dbenv, dbc->txn, &LSN(cp->page), 0,
            dbp->log_fileid, PGNO(cp->page), &LSN(cp->page), cp->indx)) != 0)
                goto err;

        /* Set the intent-to-delete flag on the page and update all cursors. */
        if (TYPE(cp->page) == P_LBTREE)
                B_DSET(GET_BKEYDATA(cp->page, cp->indx + O_INDX)->type);
        else
                B_DSET(GET_BKEYDATA(cp->page, cp->indx)->type);

        /* Mark the page dirty. */
        ret = memp_fset(dbp->mpf, cp->page, DB_MPOOL_DIRTY);

err:    /*
         * If we've been successful so far and the tree has record numbers,
         * adjust the record counts.  Either way, release any acquired pages.
         */
        if (F_ISSET(cp, C_RECNUM)) {
                if (ret == 0)
                        ret = __bam_adjust(dbc, -1);
                (void)__bam_stkrel(dbc, STK_CLRDBC);
        } else {
                DISCARD_CUR(dbc, t_ret);
                if (t_ret != 0 && ret == 0)
                        ret = t_ret;
        }

        /* Update the cursors last, after all chance of failure is past. */
        if (ret == 0)
                (void)__bam_ca_delete(dbp, cp->pgno, cp->indx, 1);

        return (ret);
}

/*
 * __bam_c_dup --
 *      Duplicate a btree cursor, such that the new one holds appropriate
 *      locks for the position of the original.
 *
 * PUBLIC: int __bam_c_dup __P((DBC *, DBC *));
 */
int
__bam_c_dup(orig_dbc, new_dbc)
        DBC *orig_dbc, *new_dbc;
{
        BTREE_CURSOR *orig, *new;
        int ret;

        orig = (BTREE_CURSOR *)orig_dbc->internal;
        new = (BTREE_CURSOR *)new_dbc->internal;

        /*
         * If we're holding a lock we need to acquire a copy of it, unless
         * we're in a transaction.  We don't need to copy any lock we're
         * holding inside a transaction because all the locks are retained
         * until the transaction commits or aborts.
         */
        if (orig->lock.off != LOCK_INVALID && orig_dbc->txn == NULL) {
                if ((ret = __db_lget(new_dbc,
                    0, new->pgno, new->lock_mode, 0, &new->lock)) != 0)
                        return (ret);
        }
        new->ovflsize = orig->ovflsize;
        new->recno = orig->recno;
        new->flags = orig->flags;

        return (0);
}

/*
 * __bam_c_get --
 *      Get using a cursor (btree).
 */
static int
__bam_c_get(dbc, key, data, flags, pgnop)
        DBC *dbc;
        DBT *key, *data;
        u_int32_t flags;
        db_pgno_t *pgnop;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        db_pgno_t orig_pgno;
        db_indx_t orig_indx;
        int exact, newopd, ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        orig_pgno = cp->pgno;
        orig_indx = cp->indx;

        newopd = 0;
        switch (flags) {
        case DB_CURRENT:
                /* It's not possible to return a deleted record. */
                if (F_ISSET(cp, C_DELETED)) {
                        ret = DB_KEYEMPTY;
                        goto err;
                }

                /*
                 * Acquire the current page.  We have at least a read-lock
                 * already.  The caller may have set DB_RMW asking for a
                 * write lock, but upgrading to a write lock has no better
                 * chance of succeeding now instead of later, so don't try.
                 */
                if ((ret = memp_fget(dbp->mpf, &cp->pgno, 0, &cp->page)) != 0)
                        goto err;
                break;
        case DB_FIRST:
                newopd = 1;
                if ((ret = __bam_c_first(dbc)) != 0)
                        goto err;
                break;
        case DB_GET_BOTH:
                /*
                 * There are two ways to get here based on DBcursor->c_get
                 * with the DB_GET_BOTH flag set:
                 *
                 * 1. Searching a sorted off-page duplicate tree: do a tree
                 * search.
                 *
                 * 2. Searching btree: do a tree search.  If it returns a
                 * reference to off-page duplicate tree, return immediately
                 * and let our caller deal with it.  If the search doesn't
                 * return a reference to off-page duplicate tree, start an
                 * on-page search.
                 */
                if (F_ISSET(dbc, DBC_OPD)) {
                        if ((ret = __bam_c_search(
                            dbc, data, DB_GET_BOTH, &exact)) != 0)
                                goto err;
                        if (!exact) {
                                ret = DB_NOTFOUND;
                                goto err;
                        }
                } else {
                        if ((ret = __bam_c_search(
                            dbc, key, DB_GET_BOTH, &exact)) != 0)
                                return (ret);
                        if (!exact) {
                                ret = DB_NOTFOUND;
                                goto err;
                        }

                        if (pgnop != NULL && __bam_isopd(dbc, pgnop)) {
                                newopd = 1;
                                break;
                        }
                        if ((ret = __bam_getboth_finddatum(dbc, data)) != 0)
                                goto err;
                }
                break;
        case DB_GET_BOTHC:
                if ((ret = __bam_getbothc(dbc, data)) != 0)
                        goto err;
                break;
        case DB_LAST:
                newopd = 1;
                if ((ret = __bam_c_last(dbc)) != 0)
                        goto err;
                break;
        case DB_NEXT:
                newopd = 1;
                if (cp->pgno == PGNO_INVALID) {
                        if ((ret = __bam_c_first(dbc)) != 0)
                                goto err;
                } else
                        if ((ret = __bam_c_next(dbc, 1)) != 0)
                                goto err;
                break;
        case DB_NEXT_DUP:
                if ((ret = __bam_c_next(dbc, 1)) != 0)
                        goto err;
                if (!IS_CUR_DUPLICATE(dbc, orig_pgno, orig_indx)) {
                        ret = DB_NOTFOUND;
                        goto err;
                }
                break;
        case DB_NEXT_NODUP:
                newopd = 1;
                if (cp->pgno == PGNO_INVALID) {
                        if ((ret = __bam_c_first(dbc)) != 0)
                                goto err;
                } else
                        do {
                                if ((ret = __bam_c_next(dbc, 1)) != 0)
                                        goto err;
                        } while (IS_CUR_DUPLICATE(dbc, orig_pgno, orig_indx));
                break;
        case DB_PREV:
                newopd = 1;
                if (cp->pgno == PGNO_INVALID) {
                        if ((ret = __bam_c_last(dbc)) != 0)
                                goto err;
                } else
                        if ((ret = __bam_c_prev(dbc)) != 0)
                                goto err;
                break;
        case DB_PREV_NODUP:
                newopd = 1;
                if (cp->pgno == PGNO_INVALID) {
                        if ((ret = __bam_c_last(dbc)) != 0)
                                goto err;
                } else
                        do {
                                if ((ret = __bam_c_prev(dbc)) != 0)
                                        goto err;
                        } while (IS_CUR_DUPLICATE(dbc, orig_pgno, orig_indx));
                break;
        case DB_SET:
        case DB_SET_RECNO:
                newopd = 1;
                if ((ret = __bam_c_search(dbc, key, flags, &exact)) != 0)
                        goto err;
                break;
        case DB_SET_RANGE:
                newopd = 1;
                if ((ret = __bam_c_search(dbc, key, flags, &exact)) != 0)
                        goto err;

                /*
                 * As we didn't require an exact match, the search function
                 * may have returned an entry past the end of the page.  Or,
                 * we may be referencing a deleted record.  If so, move to
                 * the next entry.
                 */
                if (cp->indx == NUM_ENT(cp->page) || IS_CUR_DELETED(dbc))
                        if ((ret = __bam_c_next(dbc, 0)) != 0)
                                goto err;
                break;
        default:
                ret = __db_unknown_flag(dbp->dbenv, "__bam_c_get", flags);
                goto err;
        }

        /*
         * We may have moved to an off-page duplicate tree.  Return that
         * information to our caller.
         */
        if (newopd && pgnop != NULL)
                (void)__bam_isopd(dbc, pgnop);

        /* Don't return the key, it was passed to us */
        if (flags == DB_SET)
                F_SET(key, DB_DBT_ISSET);

err:    /*
         * Regardless of whether we were successful or not, if the cursor
         * moved, clear the delete flag, DBcursor->c_get never references
         * a deleted key, if it moved at all.
         */
        if (F_ISSET(cp, C_DELETED)
            && (cp->pgno != orig_pgno || cp->indx != orig_indx))
                F_CLR(cp, C_DELETED);

        return (ret);
}

/*
 * __bam_getbothc --
 *      Search for a matching data item on a join.
 */
static int
__bam_getbothc(dbc, data)
        DBC *dbc;
        DBT *data;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        int cmp, exact, ret;

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

        /*
         * Acquire the current page.  We have at least a read-lock
         * already.  The caller may have set DB_RMW asking for a
         * write lock, but upgrading to a write lock has no better
         * chance of succeeding now instead of later, so don't try.
         */
        if ((ret = memp_fget(dbp->mpf, &cp->pgno, 0, &cp->page)) != 0)
                return (ret);

        /*
         * An off-page duplicate cursor.  Search the remaining duplicates
         * for one which matches (do a normal btree search, then verify
         * that the retrieved record is greater than the original one).
         */
        if (F_ISSET(dbc, DBC_OPD)) {
                /*
                 * Check to make sure the desired item comes strictly after
                 * the current position;  if it doesn't, return DB_NOTFOUND.
                 */
                if ((ret = __bam_cmp(dbp, data, cp->page, cp->indx,
                    dbp->dup_compare == NULL ? __bam_defcmp : dbp->dup_compare,
                    &cmp)) != 0)
                        return (ret);

                if (cmp <= 0)
                        return (DB_NOTFOUND);

                /* Discard the current page, we're going to do a full search. */
                if ((ret = memp_fput(dbp->mpf, cp->page, 0)) != 0)
                        return (ret);
                cp->page = NULL;

                return (__bam_c_search(dbc, data, DB_GET_BOTH, &exact));
        }

        /*
         * We're doing a DBC->c_get(DB_GET_BOTHC) and we're already searching
         * a set of on-page duplicates (either sorted or unsorted).  Continue
         * a linear search from after the current position.
         *
         * (Note that we could have just finished a "set" of one duplicate,
         * i.e. not a duplicate at all, but the following check will always
         * return DB_NOTFOUND in this case, which is the desired behavior.)
         */
        if (cp->indx + P_INDX >= NUM_ENT(cp->page) ||
            !IS_DUPLICATE(dbc, cp->indx, cp->indx + P_INDX))
                return (DB_NOTFOUND);
        cp->indx += P_INDX;

        return (__bam_getboth_finddatum(dbc, data));
}

/*
 * __bam_getboth_finddatum --
 *      Find a matching on-page data item.
 */
static int
__bam_getboth_finddatum(dbc, data)
        DBC *dbc;
        DBT *data;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        db_indx_t base, lim, top;
        int cmp, ret;

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

        /*
         * Called (sometimes indirectly) from DBC->get to search on-page data
         * item(s) for a matching value.  If the original flag was DB_GET_BOTH,
         * the cursor argument is set to the first data item for the key.  If
         * the original flag was DB_GET_BOTHC, the cursor argument is set to
         * the first data item that we can potentially return.  In both cases,
         * there may or may not be additional duplicate data items to search.
         *
         * If the duplicates are not sorted, do a linear search.
         *
         * If the duplicates are sorted, do a binary search.  The reason for
         * this is that large pages and small key/data pairs result in large
         * numbers of on-page duplicates before they get pushed off-page.
         */
        if (dbp->dup_compare == NULL) {
                for (;; cp->indx += P_INDX) {
                        if (!IS_CUR_DELETED(dbc) &&
                            (ret = __bam_cmp(dbp, data, cp->page,
                            cp->indx + O_INDX, __bam_defcmp, &cmp)) != 0)
                                return (ret);
                        if (cmp == 0)
                                return (0);

                        if (cp->indx + P_INDX >= NUM_ENT(cp->page) ||
                            !IS_DUPLICATE(dbc, cp->indx, cp->indx + P_INDX))
                                break;
                }
        } else {
                /*
                 * Find the top and bottom of the duplicate set.  Binary search
                 * requires at least two items, don't loop if there's only one.
                 */
                for (base = top = cp->indx;
                    top < NUM_ENT(cp->page); top += P_INDX)
                        if (!IS_DUPLICATE(dbc, cp->indx, top))
                                break;
                if (base == (top - P_INDX)) {
                        if  ((ret = __bam_cmp(dbp, data,
                            cp->page, cp->indx + O_INDX,
                            dbp->dup_compare, &cmp)) != 0)
                               return (ret);
                        return (cmp == 0 ? 0 : DB_NOTFOUND);
                }

                for (lim =
                    (top - base) / (db_indx_t)P_INDX; lim != 0; lim >>= 1) {
                        cp->indx = base + ((lim >> 1) * P_INDX);
                        if ((ret = __bam_cmp(dbp, data, cp->page,
                            cp->indx + O_INDX, dbp->dup_compare, &cmp)) != 0)
                                return (ret);
                        if (cmp == 0) {
                                if (!IS_CUR_DELETED(dbc))
                                        return (0);
                                break;
                        }
                        if (cmp > 0) {
                                base = cp->indx + P_INDX;
                                --lim;
                        }
                }
        }
        return (DB_NOTFOUND);
}

/*
 * __bam_c_put --
 *      Put using a cursor.
 */
static int
__bam_c_put(dbc, key, data, flags, pgnop)
        DBC *dbc;
        DBT *key, *data;
        u_int32_t flags;
        db_pgno_t *pgnop;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        DBT dbt;
        u_int32_t iiop;
        int cmp, exact, needkey, ret, stack;
        void *arg;

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

split:  needkey = ret = stack = 0;
        switch (flags) {
        case DB_AFTER:
        case DB_BEFORE:
        case DB_CURRENT:
                needkey = 1;
                iiop = flags;

                /*
                 * If the tree has record numbers (and we're not just replacing
                 * an existing record), we need a complete stack so that we can
                 * adjust the record counts.
                 */
                if (F_ISSET(cp, C_RECNUM) &&
                    (flags != DB_CURRENT || F_ISSET(cp, C_DELETED))) {
                        if ((ret = __bam_c_getstack(dbc)) != 0)
                                goto err;
                        stack = 1;
                } else {
                        /* Acquire the current page with a write lock. */
                        ACQUIRE_WRITE_LOCK(dbc, ret);
                        if (ret != 0)
                                goto err;
                        if ((ret = memp_fget(
                            dbp->mpf, &cp->pgno, 0, &cp->page)) != 0)
                                goto err;
                }
                break;
        case DB_KEYFIRST:
        case DB_KEYLAST:
        case DB_NODUPDATA:
                /*
                 * Searching off-page, sorted duplicate tree: do a tree search
                 * for the correct item; __bam_c_search returns the smallest
                 * slot greater than the key, use it.
                 */
                if (F_ISSET(dbc, DBC_OPD)) {
                        if ((ret =
                            __bam_c_search(dbc, data, flags, &exact)) != 0)
                                goto err;
                        stack = 1;

                        /* Disallow "sorted" duplicate duplicates. */
                        if (exact) {
                                ret = __db_duperr(dbp, flags);
                                goto err;
                        }
                        iiop = DB_BEFORE;
                        break;
                }

                /* Searching a btree. */
                if ((ret = __bam_c_search(dbc, key,
                    flags == DB_KEYFIRST || dbp->dup_compare != NULL ?
                    DB_KEYFIRST : DB_KEYLAST, &exact)) != 0)
                        goto err;
                stack = 1;

                /*
                 * If we don't have an exact match, __bam_c_search returned
                 * the smallest slot greater than the key, use it.
                 */
                if (!exact) {
                        iiop = DB_KEYFIRST;
                        break;
                }

                /*
                 * If duplicates aren't supported, replace the current item.
                 * (If implementing the DB->put function, our caller already
                 * checked the DB_NOOVERWRITE flag.)
                 */
                if (!F_ISSET(dbp, DB_AM_DUP)) {
                        iiop = DB_CURRENT;
                        break;
                }

                /*
                 * If we find a matching entry, it may be an off-page duplicate
                 * tree.  Return the page number to our caller, we need a new
                 * cursor.
                 */
                if (pgnop != NULL && __bam_isopd(dbc, pgnop))
                        goto done;

                /* If the duplicates aren't sorted, move to the right slot. */
                if (dbp->dup_compare == NULL) {
                        if (flags == DB_KEYFIRST)
                                iiop = DB_BEFORE;
                        else
                                for (;; cp->indx += P_INDX)
                                        if (cp->indx + P_INDX >=
                                            NUM_ENT(cp->page) ||
                                            !IS_DUPLICATE(dbc, cp->indx,
                                            cp->indx + P_INDX)) {
                                                iiop = DB_AFTER;
                                                break;
                                        }
                        break;
                }

                /*
                 * We know that we're looking at the first of a set of sorted
                 * on-page duplicates.  Walk the list to find the right slot.
                 */
                for (;; cp->indx += P_INDX) {
                        if ((ret = __bam_cmp(dbp, data, cp->page,
                            cp->indx + O_INDX, dbp->dup_compare, &cmp)) !=0)
                                return (ret);
                        if (cmp < 0) {
                                iiop = DB_BEFORE;
                                break;
                        }

                        /* Disallow "sorted" duplicate duplicates. */
                        if (cmp == 0) {
                                if (IS_DELETED(cp->page, cp->indx)) {
                                        iiop = DB_CURRENT;
                                        break;
                                }
                                ret = __db_duperr(dbp, flags);
                                goto err;
                        }

                        if (cp->indx + P_INDX >= NUM_ENT(cp->page) ||
                            ((PAGE *)cp->page)->inp[cp->indx] !=
                            ((PAGE *)cp->page)->inp[cp->indx + P_INDX]) {
                                iiop = DB_AFTER;
                                break;
                        }
                }
                break;
        default:
                ret = __db_unknown_flag(dbp->dbenv, "__bam_c_put", flags);
                goto err;
        }

        switch (ret = __bam_iitem(dbc, key, data, iiop, 0)) {
        case 0:
                break;
        case DB_NEEDSPLIT:
                /*
                 * To split, we need a key for the page.  Either use the key
                 * argument or get a copy of the key from the page.
                 */
                if (flags == DB_AFTER ||
                    flags == DB_BEFORE || flags == DB_CURRENT) {
                        memset(&dbt, 0, sizeof(DBT));
                        if ((ret = __db_ret(dbp, cp->page, 0, &dbt,
                            &dbc->rkey.data, &dbc->rkey.ulen)) != 0)
                                goto err;
                        arg = &dbt;
                } else
                        arg = F_ISSET(dbc, DBC_OPD) ? data : key;

                /*
                 * Discard any locks and pinned pages (the locks are discarded
                 * even if we're running with transactions, as they lock pages
                 * that we're sorry we ever acquired).  If stack is set and the
                 * cursor entries are valid, they point to the same entries as
                 * the stack, don't free them twice.
                 */
                if (stack)
                        ret = __bam_stkrel(dbc, STK_CLRDBC | STK_NOLOCK);
                else
                        DISCARD_CUR(dbc, ret);
                if (ret != 0)
                        goto err;

                /* Split the tree. */
                if ((ret = __bam_split(dbc, arg)) != 0)
                        return (ret);

                goto split;
        default:
                goto err;
        }

err:
done:   /*
         * Discard any pages pinned in the tree and their locks, except for
         * the leaf page.  Note, the leaf page participated in any stack we
         * acquired, and so we have to adjust the stack as necessary.  If
         * there was only a single page on the stack, we don't have to free
         * further stack pages.
         */
        if (stack && BT_STK_POP(cp) != NULL)
                (void)__bam_stkrel(dbc, 0);

        /*
         * Regardless of whether we were successful or not, clear the delete
         * flag.  If we're successful, we either moved the cursor or the item
         * is no longer deleted.  If we're not successful, then we're just a
         * copy, no need to have the flag set.
         */
        F_CLR(cp, C_DELETED);

        return (ret);
}

/*
 * __bam_c_rget --
 *      Return the record number for a cursor.
 *
 * PUBLIC: int __bam_c_rget __P((DBC *, DBT *, u_int32_t));
 */
int
__bam_c_rget(dbc, data, flags)
        DBC *dbc;
        DBT *data;
        u_int32_t flags;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        DBT dbt;
        db_recno_t recno;
        int exact, ret;

        COMPQUIET(flags, 0);
        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;

        /*
         * Get the page with the current item on it.
         * Get a copy of the key.
         * Release the page, making sure we don't release it twice.
         */
        if ((ret = memp_fget(dbp->mpf, &cp->pgno, 0, &cp->page)) != 0)
                return (ret);
        memset(&dbt, 0, sizeof(DBT));
        if ((ret = __db_ret(dbp, cp->page,
            cp->indx, &dbt, &dbc->rkey.data, &dbc->rkey.ulen)) != 0)
                goto err;
        ret = memp_fput(dbp->mpf, cp->page, 0);
        cp->page = NULL;
        if (ret != 0)
                return (ret);

        if ((ret = __bam_search(dbc, &dbt,
            F_ISSET(dbc, DBC_RMW) ? S_FIND_WR : S_FIND,
            1, &recno, &exact)) != 0)
                goto err;

        ret = __db_retcopy(dbp, data,
            &recno, sizeof(recno), &dbc->rdata.data, &dbc->rdata.ulen);

        /* Release the stack. */
err:    __bam_stkrel(dbc, 0);

        return (ret);
}

/*
 * __bam_c_writelock --
 *      Upgrade the cursor to a write lock.
 */
static int
__bam_c_writelock(dbc)
        DBC *dbc;
{
        BTREE_CURSOR *cp;
        int ret;

        cp = (BTREE_CURSOR *)dbc->internal;

        if (cp->lock_mode == DB_LOCK_WRITE)
                return (0);

        /*
         * When writing to an off-page duplicate tree, we need to have the
         * appropriate page in the primary tree locked.  The general DBC
         * code calls us first with the primary cursor so we can acquire the
         * appropriate lock.
         */
        ACQUIRE_WRITE_LOCK(dbc, ret);
        return (ret);
}

/*
 * __bam_c_first --
 *      Return the first record.
 */
static int
__bam_c_first(dbc)
        DBC *dbc;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        db_pgno_t pgno;
        int ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        ret = 0;

        /* Walk down the left-hand side of the tree. */
        for (pgno = cp->root;;) {
                ACQUIRE_CUR_SET(dbc, DB_LOCK_READ, pgno, ret);
                if (ret != 0)
                        return (ret);

                /* If we find a leaf page, we're done. */
                if (ISLEAF(cp->page))
                        break;

                pgno = GET_BINTERNAL(cp->page, 0)->pgno;
        }

        /* If we want a write lock instead of a read lock, get it now. */
        if (F_ISSET(dbc, DBC_RMW)) {
                ACQUIRE_WRITE_LOCK(dbc, ret);
                if (ret != 0)
                        return (ret);
        }

        /* If on an empty page or a deleted record, move to the next one. */
        if (NUM_ENT(cp->page) == 0 || IS_CUR_DELETED(dbc))
                if ((ret = __bam_c_next(dbc, 0)) != 0)
                        return (ret);

        return (0);
}

/*
 * __bam_c_last --
 *      Return the last record.
 */
static int
__bam_c_last(dbc)
        DBC *dbc;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        db_pgno_t pgno;
        int ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        ret = 0;

        /* Walk down the right-hand side of the tree. */
        for (pgno = cp->root;;) {
                ACQUIRE_CUR_SET(dbc, DB_LOCK_READ, pgno, ret);
                if (ret != 0)
                        return (ret);

                /* If we find a leaf page, we're done. */
                if (ISLEAF(cp->page))
                        break;

                pgno =
                    GET_BINTERNAL(cp->page, NUM_ENT(cp->page) - O_INDX)->pgno;
        }

        /* If we want a write lock instead of a read lock, get it now. */
        if (F_ISSET(dbc, DBC_RMW)) {
                ACQUIRE_WRITE_LOCK(dbc, ret);
                if (ret != 0)
                        return (ret);
        }

        cp->indx = NUM_ENT(cp->page) == 0 ? 0 :
            NUM_ENT(cp->page) -
            (TYPE(cp->page) == P_LBTREE ? P_INDX : O_INDX);

        /* If on an empty page or a deleted record, move to the previous one. */
        if (NUM_ENT(cp->page) == 0 || IS_CUR_DELETED(dbc))
                if ((ret = __bam_c_prev(dbc)) != 0)
                        return (ret);

        return (0);
}

/*
 * __bam_c_next --
 *      Move to the next record.
 */
static int
__bam_c_next(dbc, initial_move)
        DBC *dbc;
        int initial_move;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        db_indx_t adjust;
        db_lockmode_t lock_mode;
        db_pgno_t pgno;
        int ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        ret = 0;

        /*
         * We're either moving through a page of duplicates or a btree leaf
         * page.
         *
         * !!!
         * This code handles empty pages and pages with only deleted entries.
         */
        if (F_ISSET(dbc, DBC_OPD)) {
                adjust = O_INDX;
                lock_mode = DB_LOCK_NG;
        } else {
                adjust = dbc->dbtype == DB_BTREE ? P_INDX : O_INDX;
                lock_mode =
                    F_ISSET(dbc, DBC_RMW) ? DB_LOCK_WRITE : DB_LOCK_READ;
        }
        if (cp->page == NULL) {
                ACQUIRE_CUR(dbc, lock_mode, ret);
                if (ret != 0)
                        return (ret);
        }

        if (initial_move)
                cp->indx += adjust;

        for (;;) {
                /*
                 * If at the end of the page, move to a subsequent page.
                 *
                 * !!!
                 * Check for >= NUM_ENT.  If the original search landed us on
                 * NUM_ENT, we may have incremented indx before the test.
                 */
                if (cp->indx >= NUM_ENT(cp->page)) {
                        if ((pgno
                            = NEXT_PGNO(cp->page)) == PGNO_INVALID)
                                return (DB_NOTFOUND);

                        ACQUIRE_CUR_SET(dbc, lock_mode, pgno, ret);
                        if (ret != 0)
                                return (ret);
                        continue;
                }
                if (IS_CUR_DELETED(dbc)) {
                        cp->indx += adjust;
                        continue;
                }
                break;
        }
        return (0);
}

/*
 * __bam_c_prev --
 *      Move to the previous record.
 */
static int
__bam_c_prev(dbc)
        DBC *dbc;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        db_indx_t adjust;
        db_lockmode_t lock_mode;
        db_pgno_t pgno;
        int ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        ret = 0;

        /*
         * We're either moving through a page of duplicates or a btree leaf
         * page.
         *
         * !!!
         * This code handles empty pages and pages with only deleted entries.
         */
        if (F_ISSET(dbc, DBC_OPD)) {
                adjust = O_INDX;
                lock_mode = DB_LOCK_NG;
        } else {
                adjust = dbc->dbtype == DB_BTREE ? P_INDX : O_INDX;
                lock_mode =
                    F_ISSET(dbc, DBC_RMW) ? DB_LOCK_WRITE : DB_LOCK_READ;
        }
        if (cp->page == NULL) {
                ACQUIRE_CUR(dbc, lock_mode, ret);
                if (ret != 0)
                        return (ret);
        }

        for (;;) {
                /* If at the beginning of the page, move to a previous one. */
                if (cp->indx == 0) {
                        if ((pgno =
                            PREV_PGNO(cp->page)) == PGNO_INVALID)
                                return (DB_NOTFOUND);

                        ACQUIRE_CUR_SET(dbc, lock_mode, pgno, ret);
                        if (ret != 0)
                                return (ret);

                        if ((cp->indx = NUM_ENT(cp->page)) == 0)
                                continue;
                }

                /* Ignore deleted records. */
                cp->indx -= adjust;
                if (IS_CUR_DELETED(dbc))
                        continue;

                break;
        }
        return (0);
}

/*
 * __bam_c_search --
 *      Move to a specified record.
 */
static int
__bam_c_search(dbc, key, flags, exactp)
        DBC *dbc;
        const DBT *key;
        u_int32_t flags;
        int *exactp;
{
        BTREE *t;
        BTREE_CURSOR *cp;
        DB *dbp;
        PAGE *h;
        db_indx_t indx;
        db_pgno_t bt_lpgno;
        db_recno_t recno;
        u_int32_t sflags;
        int cmp, ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        t = dbp->bt_internal;
        ret = 0;

        /*
         * Find an entry in the database.  Discard any lock we currently hold,
         * we're going to search the tree.
         */
        DISCARD_CUR(dbc, ret);
        if (ret != 0)
                return (ret);

        switch (flags) {
        case DB_SET_RECNO:
                if ((ret = __ram_getno(dbc, key, &recno, 0)) != 0)
                        return (ret);
                sflags = (F_ISSET(dbc, DBC_RMW) ? S_FIND_WR : S_FIND) | S_EXACT;
                if ((ret = __bam_rsearch(dbc, &recno, sflags, 1, exactp)) != 0)
                        return (ret);
                break;
        case DB_SET:
        case DB_GET_BOTH:
                sflags = (F_ISSET(dbc, DBC_RMW) ? S_FIND_WR : S_FIND) | S_EXACT;
                goto search;
        case DB_SET_RANGE:
                sflags =
                    (F_ISSET(dbc, DBC_RMW) ? S_WRITE : S_READ) | S_DUPFIRST;
                goto search;
        case DB_KEYFIRST:
                sflags = S_KEYFIRST;
                goto fast_search;
        case DB_KEYLAST:
        case DB_NODUPDATA:
                sflags = S_KEYLAST;
fast_search:    /*
                 * If the application has a history of inserting into the first
                 * or last pages of the database, we check those pages first to
                 * avoid doing a full search.
                 *
                 * If the tree has record numbers, we need a complete stack so
                 * that we can adjust the record counts, so fast_search isn't
                 * possible.
                 */
                if (F_ISSET(cp, C_RECNUM))
                        goto search;

                /*
                 * !!!
                 * We do not mutex protect the t->bt_lpgno field, which means
                 * that it can only be used in an advisory manner.  If we find
                 * page we can use, great.  If we don't, we don't care, we do
                 * it the slow way instead.  Regardless, copy it into a local
                 * variable, otherwise we might acquire a lock for a page and
                 * then read a different page because it changed underfoot.
                 */
                bt_lpgno = t->bt_lpgno;

                /*
                 * If the tree has no history of insertion, do it the slow way.
                 */
                if (bt_lpgno == PGNO_INVALID)
                        goto search;

                /* Lock and retrieve the page on which we last inserted. */
                h = NULL;
                ACQUIRE(dbc,
                    DB_LOCK_WRITE, bt_lpgno, cp->lock, bt_lpgno, h, ret);
                if (ret != 0)
                        goto fast_miss;

                /*
                 * It's okay if the page type isn't right or it's empty, it
                 * just means that the world changed.
                 */
                if (TYPE(h) != P_LBTREE || NUM_ENT(h) == 0)
                        goto fast_miss;

                /*
                 * What we do here is test to see if we're at the beginning or
                 * end of the tree and if the new item sorts before/after the
                 * first/last page entry.  We don't try and catch inserts into
                 * the middle of the tree (although we could, as long as there
                 * were two keys on the page and we saved both the index and
                 * the page number of the last insert).
                 */
                if (h->next_pgno == PGNO_INVALID) {
                        indx = NUM_ENT(h) - P_INDX;
                        if ((ret = __bam_cmp(dbp,
                            key, h, indx, t->bt_compare, &cmp)) != 0)
                                return (ret);

                        if (cmp < 0)
                                goto try_begin;
                        if (cmp > 0) {
                                indx += P_INDX;
                                goto fast_hit;
                        }

                        /*
                         * Found a duplicate.  If doing DB_KEYLAST, we're at
                         * the correct position, otherwise, move to the first
                         * of the duplicates.  If we're looking at off-page
                         * duplicates, duplicate duplicates aren't permitted,
                         * so we're done.
                         */
                        if (flags == DB_KEYLAST)
                                goto fast_hit;
                        for (;
                            indx > 0 && h->inp[indx - P_INDX] == h->inp[indx];
                            indx -= P_INDX)
                                ;
                        goto fast_hit;
                }
try_begin:      if (h->prev_pgno == PGNO_INVALID) {
                        indx = 0;
                        if ((ret = __bam_cmp(dbp,
                            key, h, indx, t->bt_compare, &cmp)) != 0)
                                return (ret);

                        if (cmp > 0)
                                goto fast_miss;
                        if (cmp < 0)
                                goto fast_hit;

                        /*
                         * Found a duplicate.  If doing DB_KEYFIRST, we're at
                         * the correct position, otherwise, move to the last
                         * of the duplicates.  If we're looking at off-page
                         * duplicates, duplicate duplicates aren't permitted,
                         * so we're done.
                         */
                        if (flags == DB_KEYFIRST)
                                goto fast_hit;
                        for (;
                            indx < (db_indx_t)(NUM_ENT(h) - P_INDX) &&
                            h->inp[indx] == h->inp[indx + P_INDX];
                            indx += P_INDX)
                                ;
                        goto fast_hit;
                }
                goto fast_miss;

fast_hit:       /* Set the exact match flag, we may have found a duplicate. */
                *exactp = cmp == 0;

                /*
                 * Insert the entry in the stack.  (Our caller is likely to
                 * call __bam_stkrel() after our return.)
                 */
                BT_STK_CLR(cp);
                BT_STK_ENTER(dbp->dbenv,
                    cp, h, indx, cp->lock, cp->lock_mode, ret);
                if (ret != 0)
                        return (ret);
                break;

fast_miss:      /*
                 * This was not the right page, so we do not need to retain
                 * the lock even in the presence of transactions.
                 */
                DISCARD(dbc, 1, cp->lock, h, ret);
                if (ret != 0)
                        return (ret);

search:         if ((ret =
                    __bam_search(dbc, key, sflags, 1, NULL, exactp)) != 0)
                        return (ret);
                break;
        default:
                return (__db_unknown_flag(dbp->dbenv, "__bam_c_search", flags));
        }

        /* Initialize the cursor from the stack. */
        cp->page = cp->csp->page;
        cp->pgno = cp->csp->page->pgno;
        cp->indx = cp->csp->indx;
        cp->lock = cp->csp->lock;
        cp->lock_mode = cp->csp->lock_mode;

        /*
         * If we inserted a key into the first or last slot of the tree,
         * remember where it was so we can do it more quickly next time.
         */
        if (TYPE(cp->page) == P_LBTREE &&
            (flags == DB_KEYFIRST || flags == DB_KEYLAST))
                t->bt_lpgno =
                    (NEXT_PGNO(cp->page) == PGNO_INVALID &&
                    cp->indx >= NUM_ENT(cp->page)) ||
                    (PREV_PGNO(cp->page) == PGNO_INVALID &&
                    cp->indx == 0) ? cp->pgno : PGNO_INVALID;
        return (0);
}

/*
 * __bam_c_physdel --
 *      Physically remove an item from the page.
 */
static int
__bam_c_physdel(dbc)
        DBC *dbc;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        DBT key;
        DB_LOCK lock;
        PAGE *h;
        db_pgno_t pgno;
        int delete_page, empty_page, exact, level, ret;

        dbp = dbc->dbp;
        cp = (BTREE_CURSOR *)dbc->internal;
        delete_page = empty_page = ret = 0;

        /* If the page is going to be emptied, consider deleting it. */
        delete_page = empty_page =
            NUM_ENT(cp->page) == (TYPE(cp->page) == P_LBTREE ? 2 : 1);

        /*
         * Check if the application turned off reverse splits.  Applications
         * can't turn off reverse splits in off-page duplicate trees, that
         * space will never be reused unless the exact same key is specified.
         */
        if (delete_page &&
            !F_ISSET(dbc, DBC_OPD) && F_ISSET(dbp, DB_BT_REVSPLIT))
                delete_page = 0;

        /*
         * We never delete the last leaf page.  (Not really true -- we delete
         * the last leaf page of off-page duplicate trees, but that's handled
         * by our caller, not down here.)
         */
        if (delete_page && cp->pgno == cp->root)
                delete_page = 0;

        /*
         * To delete a leaf page other than an empty root page, we need a
         * copy of a key from the page.  Use the 0th page index since it's
         * the last key the page held.
         */
        if (delete_page) {
                memset(&key, 0, sizeof(DBT));
                if ((ret = __db_ret(dbp, cp->page,
                    0, &key, &dbc->rkey.data, &dbc->rkey.ulen)) != 0)
                        return (ret);
        }

        /*
         * Delete the items.  If page isn't empty, we adjust the cursors.
         *
         * !!!
         * The following operations to delete a page may deadlock.  The easy
         * scenario is if we're deleting an item because we're closing cursors
         * because we've already deadlocked and want to call txn_abort().  If
         * we fail due to deadlock, we'll leave a locked, possibly empty page
         * in the tree, which won't be empty long because we'll undo the delete
         * when we undo the transaction's modifications.
         *
         * !!!
         * Delete the key item first, otherwise the on-page duplicate checks
         * in __bam_ditem() won't work!
         */
        if (TYPE(cp->page) == P_LBTREE) {
                if ((ret = __bam_ditem(dbc, cp->page, cp->indx)) != 0)
                        return (ret);
                if (!empty_page)
                        if ((ret = __bam_ca_di(dbc,
                            PGNO(cp->page), cp->indx, -1)) != 0)
                                return (ret);
        }
        if ((ret = __bam_ditem(dbc, cp->page, cp->indx)) != 0)
                return (ret);
        if (!empty_page)
                if ((ret = __bam_ca_di(dbc, PGNO(cp->page), cp->indx, -1)) != 0)
                        return (ret);

        /* If we're not going to try and delete the page, we're done. */
        if (!delete_page)
                return (0);

        /*
         * Call __bam_search to reacquire the empty leaf page, but this time
         * get both the leaf page and it's parent, locked.  Jump back up the
         * tree, until we have the top pair of pages that we want to delete.
         * Once we have the top page that we want to delete locked, lock the
         * underlying pages and check to make sure they're still empty.  If
         * they are, delete them.
         */
        for (level = LEAFLEVEL;; ++level) {
                /* Acquire a page and its parent, locked. */
                if ((ret = __bam_search(
                    dbc, &key, S_WRPAIR, level, NULL, &exact)) != 0)
                        return (ret);

                /*
                 * If we reach the root or the parent page isn't going to be
                 * empty when we delete one record, stop.
                 */
                h = cp->csp[-1].page;
                if (h->pgno == cp->root || NUM_ENT(h) != 1)
                        break;

                /* Discard the stack, retaining no locks. */
                (void)__bam_stkrel(dbc, STK_NOLOCK);
        }

        /*
         * Move the stack pointer one after the last entry, we may be about
         * to push more items onto the page stack.
         */
        ++cp->csp;

        /*
         * cp->csp[-2].page is now the parent page, which we may or may not be
         * going to delete, and cp->csp[-1].page is the first page we know we
         * are going to delete.  Walk down the chain of pages, acquiring pages
         * until we've acquired a leaf page.  Generally, this shouldn't happen;
         * we should only see a single internal page with one item and a single
         * leaf page with no items.  The scenario where we could see something
         * else is if reverse splits were turned off for awhile and then turned
         * back on.  That could result in all sorts of strangeness, e.g., empty
         * pages in the tree, trees that looked like linked lists, and so on.
         *
         * !!!
         * Sheer paranoia: if we find any pages that aren't going to be emptied
         * by the delete, someone else added an item while we were walking the
         * tree, and we discontinue the delete.  Shouldn't be possible, but we
         * check regardless.
         */
        for (h = cp->csp[-1].page;;) {
                if (ISLEAF(h)) {
                        if (NUM_ENT(h) != 0)
                                break;
                        break;
                } else
                        if (NUM_ENT(h) != 1)
                                break;

                /*
                 * Get the next page, write lock it and push it onto the stack.
                 * We know it's index 0, because it can only have one element.
                 */
                switch (TYPE(h)) {
                case P_IBTREE:
                        pgno = GET_BINTERNAL(h, 0)->pgno;
                        break;
                case P_IRECNO:
                        pgno = GET_RINTERNAL(h, 0)->pgno;
                        break;
                default:
                        return (__db_pgfmt(dbp, PGNO(h)));
                }

                if ((ret =
                    __db_lget(dbc, 0, pgno, DB_LOCK_WRITE, 0, &lock)) != 0)
                        break;
                if ((ret = memp_fget(dbp->mpf, &pgno, 0, &h)) != 0)
                        break;
                BT_STK_PUSH(dbp->dbenv, cp, h, 0, lock, DB_LOCK_WRITE, ret);
                if (ret != 0)
                        break;
        }

        /* Adjust the cursor stack to reference the last page on the stack. */
        BT_STK_POP(cp);

        /*
         * If everything worked, delete the stack, otherwise, release the
         * stack and page locks without further damage.
         */
        if (ret == 0)
                ret = __bam_dpages(dbc, cp->sp);
        else
                (void)__bam_stkrel(dbc, 0);

        return (ret);
}

/*
 * __bam_c_getstack --
 *      Acquire a full stack for a cursor.
 */
static int
__bam_c_getstack(dbc)
        DBC *dbc;
{
        BTREE_CURSOR *cp;
        DB *dbp;
        DBT dbt;
        PAGE *h;
        int exact, ret, t_ret;

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

        /*
         * Get the page with the current item on it.  The caller of this
         * routine has to already hold a read lock on the page, so there
         * is no additional lock to acquire.
         */
        if ((ret = memp_fget(dbp->mpf, &cp->pgno, 0, &h)) != 0)
                return (ret);

        /* Get a copy of a key from the page. */
        memset(&dbt, 0, sizeof(DBT));
        if ((ret = __db_ret(dbp,
            h, 0, &dbt, &dbc->rkey.data, &dbc->rkey.ulen)) != 0)
                goto err;

        /* Get a write-locked stack for the page. */
        exact = 0;
        ret = __bam_search(dbc, &dbt, S_KEYFIRST, 1, NULL, &exact);

err:    /* Discard the key and the page. */
        if ((t_ret = memp_fput(dbp->mpf, h, 0)) != 0 && ret == 0)
                ret = t_ret;

        if (ret == 0) {
                /*
                 * Initialize the cursor from the stack.  We don't take the
                 * page number or page index.  The former is unchanged, but
                 * the latter may have been explicitly set by our caller and
                 * we can't change it.
                 */
                cp->page = cp->csp->page;
                cp->lock = cp->csp->lock;
                cp->lock_mode = cp->csp->lock_mode;
        }

        return (ret);
}

/*
 * __bam_isopd --
 *      Return if the cursor references an off-page duplicate tree via its
 *      page number.
 */
static int
__bam_isopd(dbc, pgnop)
        DBC *dbc;
        db_pgno_t *pgnop;
{
        BOVERFLOW *bo;

        if (TYPE(dbc->internal->page) != P_LBTREE)
                return (0);

        bo = GET_BOVERFLOW(dbc->internal->page, dbc->internal->indx + O_INDX);
        if (B_TYPE(bo->type) == B_DUPLICATE) {
                *pgnop = bo->pgno;
                return (1);
        }
        return (0);
}