usr/src/lib/libc/db/btree/bt_seq.c

/*-
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Mike Olson.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)bt_seq.c    8.1 (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>

#include <db.h>
#include "btree.h"

static int       bt_seqadv __P((BTREE *, EPG *, int));
static int       bt_seqset __P((BTREE *, EPG *, DBT *, int));

/*
 * Sequential scan support.
 *
 * The tree can be scanned sequentially, starting from either end of the tree
 * or from any specific key.  A scan request before any scanning is done is
 * initialized as starting from the least node.
 *
 * Each tree has an EPGNO which has the current position of the cursor.  The
 * cursor has to survive deletions/insertions in the tree without losing its
 * position.  This is done by noting deletions without doing them, and then
 * doing them when the cursor moves (or the tree is closed).
 */

/*
 * __BT_SEQ -- Btree sequential scan interface.
 *
 * Parameters:
 *      dbp:    pointer to access method
 *      key:    key for positioning and return value
 *      data:   data return value
 *      flags:  R_CURSOR, R_FIRST, R_LAST, R_NEXT, R_PREV.
 *
 * Returns:
 *      RET_ERROR, RET_SUCCESS or RET_SPECIAL if there's no next key.
 */
int
__bt_seq(dbp, key, data, flags)
        const DB *dbp;
        DBT *key, *data;
        u_int flags;
{
        BTREE *t;
        EPG e;
        int status;

        /*
         * If scan unitialized as yet, or starting at a specific record, set
         * the scan to a specific key.  Both bt_seqset and bt_seqadv pin the
         * page the cursor references if they're successful.
         */
        t = dbp->internal;
        switch(flags) {
        case R_NEXT:
        case R_PREV:
                if (ISSET(t, B_SEQINIT)) {
                        status = bt_seqadv(t, &e, flags);
                        break;
                }
                /* FALLTHROUGH */
        case R_CURSOR:
        case R_FIRST:
        case R_LAST:
                status = bt_seqset(t, &e, key, flags);
                break;
        default:
                errno = EINVAL;
                return (RET_ERROR);
        }

        if (status == RET_SUCCESS) {
                status = __bt_ret(t, &e, key, data);

                /* Update the actual cursor. */
                t->bt_bcursor.pgno = e.page->pgno;
                t->bt_bcursor.index = e.index;
                mpool_put(t->bt_mp, e.page, 0);
                SET(t, B_SEQINIT);
        }
        return (status);
}

/*
 * BT_SEQSET -- Set the sequential scan to a specific key.
 *
 * Parameters:
 *      t:      tree
 *      ep:     storage for returned key
 *      key:    key for initial scan position
 *      flags:  R_CURSOR, R_FIRST, R_LAST, R_NEXT, R_PREV
 *
 * Side effects:
 *      Pins the page the cursor references.
 *
 * Returns:
 *      RET_ERROR, RET_SUCCESS or RET_SPECIAL if there's no next key.
 */
static int
bt_seqset(t, ep, key, flags)
        BTREE *t;
        EPG *ep;
        DBT *key;
        int flags;
{
        EPG *e;
        PAGE *h;
        pgno_t pg;
        int exact;

        /*
         * Delete any already deleted record that we've been saving because
         * the cursor pointed to it.  Since going to a specific key, should
         * delete any logically deleted records so they aren't found.
         */
        if (ISSET(t, B_DELCRSR) && __bt_crsrdel(t, &t->bt_bcursor))
                return (RET_ERROR);

        /*
         * Find the first, last or specific key in the tree and point the cursor
         * at it.  The cursor may not be moved until a new key has been found.
         */
        switch(flags) {
        case R_CURSOR:                          /* Keyed scan. */
                /*
                 * Find the first instance of the key or the smallest key which
                 * is greater than or equal to the specified key.  If run out
                 * of keys, return RET_SPECIAL.
                 */
                if (key->data == NULL || key->size == 0) {
                        errno = EINVAL;
                        return (RET_ERROR);
                }
                e = __bt_first(t, key, &exact); /* Returns pinned page. */
                if (e == NULL)
                        return (RET_ERROR);
                /*
                 * If at the end of a page, skip any empty pages and find the
                 * next entry.
                 */
                if (e->index == NEXTINDEX(e->page)) {
                        h = e->page;
                        do {
                                pg = h->nextpg;
                                mpool_put(t->bt_mp, h, 0);
                                if (pg == P_INVALID)
                                        return (RET_SPECIAL);
                                if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                                        return (RET_ERROR);
                        } while (NEXTINDEX(h) == 0);
                        e->index = 0;
                        e->page = h;
                }
                *ep = *e;
                break;
        case R_FIRST:                           /* First record. */
        case R_NEXT:
                /* Walk down the left-hand side of the tree. */
                for (pg = P_ROOT;;) {
                        if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                                return (RET_ERROR);
                        if (h->flags & (P_BLEAF | P_RLEAF))
                                break;
                        pg = GETBINTERNAL(h, 0)->pgno;
                        mpool_put(t->bt_mp, h, 0);
                }

                /* Skip any empty pages. */
                while (NEXTINDEX(h) == 0 && h->nextpg != P_INVALID) {
                        pg = h->nextpg;
                        mpool_put(t->bt_mp, h, 0);
                        if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                                return (RET_ERROR);
                }

                if (NEXTINDEX(h) == 0) {
                        mpool_put(t->bt_mp, h, 0);
                        return (RET_SPECIAL);
                }

                ep->page = h;
                ep->index = 0;
                break;
        case R_LAST:                            /* Last record. */
        case R_PREV:
                /* Walk down the right-hand side of the tree. */
                for (pg = P_ROOT;;) {
                        if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                                return (RET_ERROR);
                        if (h->flags & (P_BLEAF | P_RLEAF))
                                break;
                        pg = GETBINTERNAL(h, NEXTINDEX(h) - 1)->pgno;
                        mpool_put(t->bt_mp, h, 0);
                }

                /* Skip any empty pages. */
                while (NEXTINDEX(h) == 0 && h->prevpg != P_INVALID) {
                        pg = h->prevpg;
                        mpool_put(t->bt_mp, h, 0);
                        if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                                return (RET_ERROR);
                }

                if (NEXTINDEX(h) == 0) {
                        mpool_put(t->bt_mp, h, 0);
                        return (RET_SPECIAL);
                }

                ep->page = h;
                ep->index = NEXTINDEX(h) - 1;
                break;
        }
        return (RET_SUCCESS);
}

/*
 * BT_SEQADVANCE -- Advance the sequential scan.
 *
 * Parameters:
 *      t:      tree
 *      flags:  R_NEXT, R_PREV
 *
 * Side effects:
 *      Pins the page the new key/data record is on.
 *
 * Returns:
 *      RET_ERROR, RET_SUCCESS or RET_SPECIAL if there's no next key.
 */
static int
bt_seqadv(t, e, flags)
        BTREE *t;
        EPG *e;
        int flags;
{
        EPGNO *c, delc;
        PAGE *h;
        indx_t index;
        pgno_t pg;

        /* Save the current cursor if going to delete it. */
        c = &t->bt_bcursor;
        if (ISSET(t, B_DELCRSR))
                delc = *c;

        if ((h = mpool_get(t->bt_mp, c->pgno, 0)) == NULL)
                return (RET_ERROR);

        /*
         * Find the next/previous record in the tree and point the cursor at it.
         * The cursor may not be moved until a new key has been found.
         */
        index = c->index;
        switch(flags) {
        case R_NEXT:                    /* Next record. */
                if (++index == NEXTINDEX(h)) {
                        do {
                                pg = h->nextpg;
                                mpool_put(t->bt_mp, h, 0);
                                if (pg == P_INVALID)
                                        return (RET_SPECIAL);
                                if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                                        return (RET_ERROR);
                        } while (NEXTINDEX(h) == 0);
                        index = 0;
                }
                break;
        case R_PREV:                    /* Previous record. */
                if (index-- == 0) {
                        do {
                                pg = h->prevpg;
                                mpool_put(t->bt_mp, h, 0);
                                if (pg == P_INVALID)
                                        return (RET_SPECIAL);
                                if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                                        return (RET_ERROR);
                        } while (NEXTINDEX(h) == 0);
                        index = NEXTINDEX(h) - 1;
                }
                break;
        }

        e->page = h;
        e->index = index;

        /*
         * Delete any already deleted record that we've been saving because the
         * cursor pointed to it.  This could cause the new index to be shifted
         * down by one if the record we're deleting is on the same page and has
         * a larger index.
         */
        if (ISSET(t, B_DELCRSR)) {
                CLR(t, B_DELCRSR);                      /* Don't try twice. */
                if (c->pgno == delc.pgno && c->index > delc.index)
                        --c->index;
                if (__bt_crsrdel(t, &delc))
                        return (RET_ERROR);
        }
        return (RET_SUCCESS);
}

/*
 * __BT_CRSRDEL -- Delete the record referenced by the cursor.
 *
 * Parameters:
 *      t:      tree
 *
 * Returns:
 *      RET_ERROR, RET_SUCCESS
 */
int
__bt_crsrdel(t, c)
        BTREE *t;
        EPGNO *c;
{
        PAGE *h;
        int status;

        CLR(t, B_DELCRSR);                      /* Don't try twice. */
        if ((h = mpool_get(t->bt_mp, c->pgno, 0)) == NULL)
                return (RET_ERROR);
        status = __bt_dleaf(t, h, c->index);
        mpool_put(t->bt_mp, h, MPOOL_DIRTY);
        return (status);
}