bt_split.c

asterisk 一个模拟IPPBX的源代码

	 * Split right.  The key/data pairs aren't sorted in the btree page so
	 * it's simpler to copy the data from the split page onto two new pages
	 * instead of copying half the data to the right page and compacting
	 * the left page in place.  Since the left page can't change, we have
	 * to swap the original and the allocated left page after the split.
	 */
	tp = bt_psplit(t, h, l, r, skip, ilen);

	/* Move the new left page onto the old left page. */
	memmove(h, l, t->bt_psize);
	if (tp == l)
		tp = h;
	free(l);

	*lp = h;
	*rp = r;
	return (tp);
}

/*
 * BT_ROOT -- Split the root page of a btree.
 *
 * Parameters:
 *	t:	tree
 *	h:	root page
 *	lp:	pointer to left page pointer
 *	rp:	pointer to right page pointer
 *	skip:	pointer to index to leave open
 *	ilen:	insert length
 *
 * Returns:
 *	Pointer to page in which to insert or NULL on error.
 */
static PAGE *
bt_root(t, h, lp, rp, skip, ilen)
	BTREE *t;
	PAGE *h, **lp, **rp;
	indx_t *skip;
	size_t ilen;
{
	PAGE *l, *r, *tp;
	pgno_t lnpg, rnpg;

#ifdef STATISTICS
	++bt_split;
	++bt_rootsplit;
#endif
	/* Put the new left and right pages for the split into place. */
	if ((l = __bt_new(t, &lnpg)) == NULL ||
	    (r = __bt_new(t, &rnpg)) == NULL)
		return (NULL);
	l->pgno = lnpg;
	r->pgno = rnpg;
	l->nextpg = r->pgno;
	r->prevpg = l->pgno;
	l->prevpg = r->nextpg = P_INVALID;
	l->lower = r->lower = BTDATAOFF;
	l->upper = r->upper = t->bt_psize;
	l->flags = r->flags = h->flags & P_TYPE;

	/* Split the root page. */
	tp = bt_psplit(t, h, l, r, skip, ilen);

	*lp = l;
	*rp = r;
	return (tp);
}

/*
 * BT_RROOT -- Fix up the recno root page after it has been split.
 *
 * Parameters:
 *	t:	tree
 *	h:	root page
 *	l:	left page
 *	r:	right page
 *
 * Returns:
 *	RET_ERROR, RET_SUCCESS
 */
static int
bt_rroot(t, h, l, r)
	BTREE *t;
	PAGE *h, *l, *r;
{
	char *dest;

	/* Insert the left and right keys, set the header information. */
	h->linp[0] = h->upper = t->bt_psize - NRINTERNAL;
	dest = (char *)h + h->upper;
	WR_RINTERNAL(dest,
	    l->flags & P_RLEAF ? NEXTINDEX(l) : rec_total(l), l->pgno);

	h->linp[1] = h->upper -= NRINTERNAL;
	dest = (char *)h + h->upper;
	WR_RINTERNAL(dest,
	    r->flags & P_RLEAF ? NEXTINDEX(r) : rec_total(r), r->pgno);

	h->lower = BTDATAOFF + 2 * sizeof(indx_t);

	/* Unpin the root page, set to recno internal page. */
	h->flags &= ~P_TYPE;
	h->flags |= P_RINTERNAL;
	mpool_put(t->bt_mp, h, MPOOL_DIRTY);

	return (RET_SUCCESS);
}

/*
 * BT_BROOT -- Fix up the btree root page after it has been split.
 *
 * Parameters:
 *	t:	tree
 *	h:	root page
 *	l:	left page
 *	r:	right page
 *
 * Returns:
 *	RET_ERROR, RET_SUCCESS
 */
static int
bt_broot(t, h, l, r)
	BTREE *t;
	PAGE *h, *l, *r;
{
	BINTERNAL *bi;
	BLEAF *bl;
	u_int32_t nbytes;
	char *dest;

	/*
	 * 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.
	 *
	 * The btree comparison code guarantees that the left-most key on any
	 * level of the tree is never used, so it doesn't need to be filled in.
	 */
	nbytes = NBINTERNAL(0);
	h->linp[0] = h->upper = t->bt_psize - nbytes;
	dest = (char *)h + h->upper;
	WR_BINTERNAL(dest, 0, l->pgno, 0);

	switch (h->flags & P_TYPE) {
	case P_BLEAF:
		bl = GETBLEAF(r, 0);
		nbytes = NBINTERNAL(bl->ksize);
		h->linp[1] = h->upper -= nbytes;
		dest = (char *)h + h->upper;
		WR_BINTERNAL(dest, bl->ksize, r->pgno, 0);
		memmove(dest, bl->bytes, bl->ksize);

		/*
		 * If the key is on an overflow page, mark the overflow chain
		 * so it isn't deleted when the leaf copy of the key is deleted.
		 */
		if (bl->flags & P_BIGKEY &&
		    bt_preserve(t, *(pgno_t *)bl->bytes) == RET_ERROR)
			return (RET_ERROR);
		break;
	case P_BINTERNAL:
		bi = GETBINTERNAL(r, 0);
		nbytes = NBINTERNAL(bi->ksize);
		h->linp[1] = h->upper -= nbytes;
		dest = (char *)h + h->upper;
		memmove(dest, bi, nbytes);
		((BINTERNAL *)dest)->pgno = r->pgno;
		break;
	default:
		abort();
	}

	/* There are two keys on the page. */
	h->lower = BTDATAOFF + 2 * sizeof(indx_t);

	/* Unpin the root page, set to btree internal page. */
	h->flags &= ~P_TYPE;
	h->flags |= P_BINTERNAL;
	mpool_put(t->bt_mp, h, MPOOL_DIRTY);

	return (RET_SUCCESS);
}

/*
 * BT_PSPLIT -- Do the real work of splitting the page.
 *
 * Parameters:
 *	t:	tree
 *	h:	page to be split
 *	l:	page to put lower half of data
 *	r:	page to put upper half of data
 *	pskip:	pointer to index to leave open
 *	ilen:	insert length
 *
 * Returns:
 *	Pointer to page in which to insert.
 */
static PAGE *
bt_psplit(t, h, l, r, pskip, ilen)
	BTREE *t;
	PAGE *h, *l, *r;
	indx_t *pskip;
	size_t ilen;
{
	BINTERNAL *bi;
	BLEAF *bl;
	CURSOR *c;
	RLEAF *rl;
	PAGE *rval;
	void *src = 0;
	indx_t full, half, nxt, off, skip, top, used;
	u_int32_t nbytes;
	int bigkeycnt, isbigkey;

	/*
	 * Split the data to the left and right pages.  Leave the skip index
	 * open.  Additionally, make some effort not to split on an overflow
	 * key.  This makes internal page processing faster and can save
	 * space as overflow keys used by internal pages are never deleted.
	 */
	bigkeycnt = 0;
	skip = *pskip;
	full = t->bt_psize - BTDATAOFF;
	half = full / 2;
	used = 0;
	for (nxt = off = 0, top = NEXTINDEX(h); nxt < top; ++off) {
		if (skip == off) {
			nbytes = ilen;
			isbigkey = 0;		/* XXX: not really known. */
		} else
			switch (h->flags & P_TYPE) {
			case P_BINTERNAL:
				src = bi = GETBINTERNAL(h, nxt);
				nbytes = NBINTERNAL(bi->ksize);
				isbigkey = bi->flags & P_BIGKEY;
				break;
			case P_BLEAF:
				src = bl = GETBLEAF(h, nxt);
				nbytes = NBLEAF(bl);
				isbigkey = bl->flags & P_BIGKEY;
				break;
			case P_RINTERNAL:
				src = GETRINTERNAL(h, nxt);
				nbytes = NRINTERNAL;
				isbigkey = 0;
				break;
			case P_RLEAF:
				src = rl = GETRLEAF(h, nxt);
				nbytes = NRLEAF(rl);
				isbigkey = 0;
				break;
			default:
				abort();
			}

		/*
		 * If the key/data pairs are substantial fractions of the max
		 * possible size for the page, it's possible to get situations
		 * where we decide to try and copy too much onto the left page.
		 * Make sure that doesn't happen.
		 */
		if ((skip <= off && used + nbytes + sizeof(indx_t) >= full)
		    || nxt == top - 1) {
			--off;
			break;
		}

		/* Copy the key/data pair, if not the skipped index. */
		if (skip != off) {
			++nxt;

			l->linp[off] = l->upper -= nbytes;
			memmove((char *)l + l->upper, src, nbytes);
		}

		used += nbytes + sizeof(indx_t);
		if (used >= half) {
			if (!isbigkey || bigkeycnt == 3)
				break;
			else
				++bigkeycnt;
		}
	}

	/*
	 * Off is the last offset that's valid for the left page.
	 * Nxt is the first offset to be placed on the right page.
	 */
	l->lower += (off + 1) * sizeof(indx_t);

	/*
	 * If splitting the page that the cursor was on, the cursor has to be
	 * adjusted to point to the same record as before the split.  If the
	 * cursor is at or past the skipped slot, the cursor is incremented by
	 * one.  If the cursor is on the right page, it is decremented by the
	 * number of records split to the left page.
	 */
	c = &t->bt_cursor;
	if (F_ISSET(c, CURS_INIT) && c->pg.pgno == h->pgno) {
		if (c->pg.index >= skip)
			++c->pg.index;
		if (c->pg.index < nxt)			/* Left page. */
			c->pg.pgno = l->pgno;
		else {					/* Right page. */
			c->pg.pgno = r->pgno;
			c->pg.index -= nxt;
		}
	}

	/*
	 * If the skipped index was on the left page, just return that page.
	 * Otherwise, adjust the skip index to reflect the new position on
	 * the right page.
	 */
	if (skip <= off) {
		skip = 0;
		rval = l;
	} else {
		rval = r;
		*pskip -= nxt;
	}

	for (off = 0; nxt < top; ++off) {
		if (skip == nxt) {
			++off;
			skip = 0;
		}
		switch (h->flags & P_TYPE) {
		case P_BINTERNAL:
			src = bi = GETBINTERNAL(h, nxt);
			nbytes = NBINTERNAL(bi->ksize);
			break;
		case P_BLEAF:
			src = bl = GETBLEAF(h, nxt);
			nbytes = NBLEAF(bl);
			break;
		case P_RINTERNAL:
			src = GETRINTERNAL(h, nxt);
			nbytes = NRINTERNAL;
			break;
		case P_RLEAF:
			src = rl = GETRLEAF(h, nxt);
			nbytes = NRLEAF(rl);
			break;
		default:
			abort();
		}
		++nxt;
		r->linp[off] = r->upper -= nbytes;
		memmove((char *)r + r->upper, src, nbytes);
	}
	r->lower += off * sizeof(indx_t);

	/* If the key is being appended to the page, adjust the index. */
	if (skip == top)
		r->lower += sizeof(indx_t);

	return (rval);
}

/*
 * BT_PRESERVE -- Mark a chain of pages as used by an internal node.
 *
 * Chains of indirect blocks pointed to by leaf nodes get reclaimed when the
 * record that references them gets deleted.  Chains pointed to by internal
 * pages never get deleted.  This routine marks a chain as pointed to by an
 * internal page.
 *
 * Parameters:
 *	t:	tree
 *	pg:	page number of first page in the chain.
 *
 * Returns:
 *	RET_SUCCESS, RET_ERROR.
 */
static int
bt_preserve(t, pg)
	BTREE *t;
	pgno_t pg;
{
	PAGE *h;

	if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
		return (RET_ERROR);
	h->flags |= P_PRESERVE;
	mpool_put(t->bt_mp, h, MPOOL_DIRTY);
	return (RET_SUCCESS);
}

/*
 * REC_TOTAL -- Return the number of recno entries below a page.
 *
 * Parameters:
 *	h:	page
 *
 * Returns:
 *	The number of recno entries below a page.
 *
 * XXX
 * These values could be set by the bt_psplit routine.  The problem is that the
 * entry has to be popped off of the stack etc. or the values have to be passed
 * all the way back to bt_split/bt_rroot and it's not very clean.
 */
static recno_t
rec_total(h)
	PAGE *h;
{
	recno_t recs;
	indx_t nxt, top;

	for (recs = 0, nxt = 0, top = NEXTINDEX(h); nxt < top; ++nxt)
		recs += GETRINTERNAL(h, nxt)->nrecs;
	return (recs);
}