nbtsort.c

PostgreSQL7.4.6 for Linux

 * A leaf page being built looks like:
 *
 * +----------------+---------------------------------+
 * | PageHeaderData | linp0 linp1 linp2 ...			  |
 * +-----------+----+---------------------------------+
 * | ... linpN |									  |
 * +-----------+--------------------------------------+
 * |	 ^ last										  |
 * |												  |
 * +-------------+------------------------------------+
 * |			 | itemN ...						  |
 * +-------------+------------------+-----------------+
 * |		  ... item3 item2 item1 | "special space" |
 * +--------------------------------+-----------------+
 *
 * Contrast this with the diagram in bufpage.h; note the mismatch
 * between linps and items.  This is because we reserve linp0 as a
 * placeholder for the pointer to the "high key" item; when we have
 * filled up the page, we will set linp0 to point to itemN and clear
 * linpN.  On the other hand, if we find this is the last (rightmost)
 * page, we leave the items alone and slide the linp array over.
 *
 * 'last' pointer indicates the last offset added to the page.
 *----------
 */
static void
_bt_buildadd(Relation index, BTPageState *state, BTItem bti)
{
	Buffer		nbuf;
	Page		npage;
	OffsetNumber last_off;
	Size		pgspc;
	Size		btisz;

	nbuf = state->btps_buf;
	npage = state->btps_page;
	last_off = state->btps_lastoff;

	pgspc = PageGetFreeSpace(npage);
	btisz = BTITEMSZ(bti);
	btisz = MAXALIGN(btisz);

	/*
	 * Check whether the item can fit on a btree page at all. (Eventually,
	 * we ought to try to apply TOAST methods if not.) We actually need to
	 * be able to fit three items on every page, so restrict any one item
	 * to 1/3 the per-page available space. Note that at this point, btisz
	 * doesn't include the ItemId.
	 *
	 * NOTE: similar code appears in _bt_insertonpg() to defend against
	 * oversize items being inserted into an already-existing index. But
	 * during creation of an index, we don't go through there.
	 */
	if (btisz > BTMaxItemSize(npage))
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
				 errmsg("index row size %lu exceeds btree maximum, %lu",
						(unsigned long) btisz,
						(unsigned long) BTMaxItemSize(npage))));

	if (pgspc < btisz || pgspc < state->btps_full)
	{
		/*
		 * Item won't fit on this page, or we feel the page is full enough
		 * already.  Finish off the page and write it out.
		 */
		Buffer		obuf = nbuf;
		Page		opage = npage;
		ItemId		ii;
		ItemId		hii;
		BTItem		obti;

		/* Create new page on same level */
		_bt_blnewpage(index, &nbuf, &npage, state->btps_level);

		/*
		 * We copy the last item on the page into the new page, and then
		 * rearrange the old page so that the 'last item' becomes its high
		 * key rather than a true data item.  There had better be at least
		 * two items on the page already, else the page would be empty of
		 * useful data.  (Hence, we must allow pages to be packed at least
		 * 2/3rds full; the 70% figure used above is close to minimum.)
		 */
		Assert(last_off > P_FIRSTKEY);
		ii = PageGetItemId(opage, last_off);
		obti = (BTItem) PageGetItem(opage, ii);
		_bt_sortaddtup(npage, ItemIdGetLength(ii), obti, P_FIRSTKEY);

		/*
		 * Move 'last' into the high key position on opage
		 */
		hii = PageGetItemId(opage, P_HIKEY);
		*hii = *ii;
		ii->lp_flags &= ~LP_USED;
		((PageHeader) opage)->pd_lower -= sizeof(ItemIdData);

		/*
		 * Link the old buffer into its parent, using its minimum key. If
		 * we don't have a parent, we have to create one; this adds a new
		 * btree level.
		 */
		if (state->btps_next == (BTPageState *) NULL)
			state->btps_next = _bt_pagestate(index, state->btps_level + 1);

		Assert(state->btps_minkey != NULL);
		ItemPointerSet(&(state->btps_minkey->bti_itup.t_tid),
					   BufferGetBlockNumber(obuf), P_HIKEY);
		_bt_buildadd(index, state->btps_next, state->btps_minkey);
		pfree((void *) state->btps_minkey);

		/*
		 * Save a copy of the minimum key for the new page.  We have to
		 * copy it off the old page, not the new one, in case we are not
		 * at leaf level.
		 */
		state->btps_minkey = _bt_formitem(&(obti->bti_itup));

		/*
		 * Set the sibling links for both pages.
		 */
		{
			BTPageOpaque oopaque = (BTPageOpaque) PageGetSpecialPointer(opage);
			BTPageOpaque nopaque = (BTPageOpaque) PageGetSpecialPointer(npage);

			oopaque->btpo_next = BufferGetBlockNumber(nbuf);
			nopaque->btpo_prev = BufferGetBlockNumber(obuf);
			nopaque->btpo_next = P_NONE;		/* redundant */
		}

		/*
		 * Write out the old page.	We never want to see it again, so we
		 * can give up our lock.
		 */
		_bt_blwritepage(index, obuf);

		/*
		 * Reset last_off to point to new page
		 */
		last_off = P_FIRSTKEY;
	}

	/*
	 * If the new item is the first for its page, stash a copy for later.
	 * Note this will only happen for the first item on a level; on later
	 * pages, the first item for a page is copied from the prior page in
	 * the code above.
	 */
	if (last_off == P_HIKEY)
	{
		Assert(state->btps_minkey == NULL);
		state->btps_minkey = _bt_formitem(&(bti->bti_itup));
	}

	/*
	 * Add the new item into the current page.
	 */
	last_off = OffsetNumberNext(last_off);
	_bt_sortaddtup(npage, btisz, bti, last_off);

	state->btps_buf = nbuf;
	state->btps_page = npage;
	state->btps_lastoff = last_off;
}

/*
 * Finish writing out the completed btree.
 */
static void
_bt_uppershutdown(Relation index, BTPageState *state)
{
	BTPageState *s;
	BlockNumber	rootblkno = P_NONE;
	uint32		rootlevel = 0;

	/*
	 * Each iteration of this loop completes one more level of the tree.
	 */
	for (s = state; s != (BTPageState *) NULL; s = s->btps_next)
	{
		BlockNumber blkno;
		BTPageOpaque opaque;

		blkno = BufferGetBlockNumber(s->btps_buf);
		opaque = (BTPageOpaque) PageGetSpecialPointer(s->btps_page);

		/*
		 * We have to link the last page on this level to somewhere.
		 *
		 * If we're at the top, it's the root, so attach it to the metapage.
		 * Otherwise, add an entry for it to its parent using its minimum
		 * key.  This may cause the last page of the parent level to
		 * split, but that's not a problem -- we haven't gotten to it yet.
		 */
		if (s->btps_next == (BTPageState *) NULL)
		{
			opaque->btpo_flags |= BTP_ROOT;
			rootblkno = blkno;
			rootlevel = s->btps_level;
		}
		else
		{
			Assert(s->btps_minkey != NULL);
			ItemPointerSet(&(s->btps_minkey->bti_itup.t_tid),
						   blkno, P_HIKEY);
			_bt_buildadd(index, s->btps_next, s->btps_minkey);
			pfree((void *) s->btps_minkey);
			s->btps_minkey = NULL;
		}

		/*
		 * This is the rightmost page, so the ItemId array needs to be
		 * slid back one slot.	Then we can dump out the page.
		 */
		_bt_slideleft(index, s->btps_buf, s->btps_page);
		_bt_blwritepage(index, s->btps_buf);
	}

	/*
	 * As the last step in the process, update the metapage to point to
	 * the new root (unless we had no data at all, in which case it's
	 * left pointing to "P_NONE").  This changes the index to the "valid"
	 * state by updating its magic number.
	 */
	_bt_metaproot(index, rootblkno, rootlevel);
}

/*
 * Read tuples in correct sort order from tuplesort, and load them into
 * btree leaves.
 */
static void
_bt_load(Relation index, BTSpool *btspool, BTSpool *btspool2)
{
	BTPageState *state = NULL;
	bool		merge = (btspool2 != NULL);
	BTItem		bti,
				bti2 = NULL;
	bool		should_free,
				should_free2,
				load1;
	TupleDesc	tupdes = RelationGetDescr(index);
	int			i,
				keysz = RelationGetNumberOfAttributes(index);
	ScanKey		indexScanKey = NULL;

	if (merge)
	{
		/*
		 * Another BTSpool for dead tuples exists. Now we have to merge
		 * btspool and btspool2.
		 */
		ScanKey		entry;
		Datum		attrDatum1,
					attrDatum2;
		bool		isFirstNull,
					isSecondNull;
		int32		compare;

		/* the preparation of merge */
		bti = (BTItem) tuplesort_getindextuple(btspool->sortstate, true, &should_free);
		bti2 = (BTItem) tuplesort_getindextuple(btspool2->sortstate, true, &should_free2);
		indexScanKey = _bt_mkscankey_nodata(index);
		for (;;)
		{
			load1 = true;		/* load BTSpool next ? */
			if (NULL == bti2)
			{
				if (NULL == bti)
					break;
			}
			else if (NULL != bti)
			{

				for (i = 1; i <= keysz; i++)
				{
					entry = indexScanKey + i - 1;
					attrDatum1 = index_getattr((IndexTuple) bti, i, tupdes, &isFirstNull);
					attrDatum2 = index_getattr((IndexTuple) bti2, i, tupdes, &isSecondNull);
					if (isFirstNull)
					{
						if (!isSecondNull)
						{
							load1 = false;
							break;
						}
					}
					else if (isSecondNull)
						break;
					else
					{
						compare = DatumGetInt32(FunctionCall2(&entry->sk_func, attrDatum1, attrDatum2));
						if (compare > 0)
						{
							load1 = false;
							break;
						}
						else if (compare < 0)
							break;
					}
				}
			}
			else
				load1 = false;

			/* When we see first tuple, create first index page */
			if (state == NULL)
				state = _bt_pagestate(index, 0);

			if (load1)
			{
				_bt_buildadd(index, state, bti);
				if (should_free)
					pfree((void *) bti);
				bti = (BTItem) tuplesort_getindextuple(btspool->sortstate, true, &should_free);
			}
			else
			{
				_bt_buildadd(index, state, bti2);
				if (should_free2)
					pfree((void *) bti2);
				bti2 = (BTItem) tuplesort_getindextuple(btspool2->sortstate, true, &should_free2);
			}
		}
		_bt_freeskey(indexScanKey);
	}
	else
	{
		/* merge is unnecessary */
		while (bti = (BTItem) tuplesort_getindextuple(btspool->sortstate, true, &should_free), bti != (BTItem) NULL)
		{
			/* When we see first tuple, create first index page */
			if (state == NULL)
				state = _bt_pagestate(index, 0);

			_bt_buildadd(index, state, bti);
			if (should_free)
				pfree((void *) bti);
		}
	}

	/* Close down final pages and rewrite the metapage */
	_bt_uppershutdown(index, state);
}