*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.60 2000/07/21 06:42:32 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.61 2000/07/21 19:21:00 tgl Exp $
*
*-------------------------------------------------------------------------
*/
/*
* Do we need to split the page to fit the item on it?
+ *
+ * Note: PageGetFreeSpace() subtracts sizeof(ItemIdData) from its
+ * result, so this comparison is correct even though we appear to
+ * be accounting only for the item and not for its line pointer.
*/
if (PageGetFreeSpace(page) < itemsz)
{
FindSplitData state;
int leftspace,
rightspace,
+ goodenough,
dataitemtotal,
dataitemstoleft;
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
+ /* Passed-in newitemsz is MAXALIGNED but does not include line pointer */
+ newitemsz += sizeof(ItemIdData);
state.newitemsz = newitemsz;
state.non_leaf = ! P_ISLEAF(opaque);
state.have_split = false;
MAXALIGN(sizeof(BTPageOpaqueData))
+ sizeof(ItemIdData);
+ /*
+ * Finding the best possible split would require checking all the possible
+ * split points, because of the high-key and left-key special cases.
+ * That's probably more work than it's worth; instead, stop as soon as
+ * we find a "good-enough" split, where good-enough is defined as an
+ * imbalance in free space of no more than pagesize/16 (arbitrary...)
+ * This should let us stop near the middle on most pages, instead of
+ * plowing to the end.
+ */
+ goodenough = leftspace / 16;
+
/* The right page will have the same high key as the old page */
if (!P_RIGHTMOST(opaque))
{
itemid = PageGetItemId(page, P_HIKEY);
- rightspace -= (int) (ItemIdGetLength(itemid) + sizeof(ItemIdData));
+ rightspace -= (int) (MAXALIGN(ItemIdGetLength(itemid)) +
+ sizeof(ItemIdData));
}
/* Count up total space in data items without actually scanning 'em */
/*
* Scan through the data items and calculate space usage for a split
- * at each possible position. XXX we could probably stop somewhere
- * near the middle...
+ * at each possible position.
*/
dataitemstoleft = 0;
maxoff = PageGetMaxOffsetNumber(page);
rightfree;
itemid = PageGetItemId(page, offnum);
- itemsz = ItemIdGetLength(itemid) + sizeof(ItemIdData);
+ itemsz = MAXALIGN(ItemIdGetLength(itemid)) + sizeof(ItemIdData);
/*
* We have to allow for the current item becoming the high key of
- * the left page; therefore it counts against left space.
+ * the left page; therefore it counts against left space as well
+ * as right space.
*/
leftfree = leftspace - dataitemstoleft - (int) itemsz;
rightfree = rightspace - (dataitemtotal - dataitemstoleft);
- if (offnum < newitemoff)
- _bt_checksplitloc(&state, offnum, leftfree, rightfree,
- false, itemsz);
- else if (offnum > newitemoff)
+ /*
+ * Will the new item go to left or right of split?
+ */
+ if (offnum > newitemoff)
_bt_checksplitloc(&state, offnum, leftfree, rightfree,
true, itemsz);
+ else if (offnum < newitemoff)
+ _bt_checksplitloc(&state, offnum, leftfree, rightfree,
+ false, itemsz);
else
{
- /* need to try it both ways!! */
- _bt_checksplitloc(&state, offnum, leftfree, rightfree,
- false, newitemsz);
+ /* need to try it both ways! */
_bt_checksplitloc(&state, offnum, leftfree, rightfree,
true, itemsz);
+ /* here we are contemplating newitem as first on right */
+ _bt_checksplitloc(&state, offnum, leftfree, rightfree,
+ false, newitemsz);
}
+ /* Abort scan once we find a good-enough choice */
+ if (state.have_split && state.best_delta <= goodenough)
+ break;
+
dataitemstoleft += itemsz;
}
+ /*
+ * I believe it is not possible to fail to find a feasible split,
+ * but just in case ...
+ */
if (! state.have_split)
elog(FATAL, "_bt_findsplitloc: can't find a feasible split point for %s",
RelationGetRelationName(rel));
+
*newitemonleft = state.newitemonleft;
return state.firstright;
}
+/*
+ * Subroutine to analyze a particular possible split choice (ie, firstright
+ * and newitemonleft settings), and record the best split so far in *state.
+ */
static void
_bt_checksplitloc(FindSplitData *state, OffsetNumber firstright,
int leftfree, int rightfree,
bool newitemonleft, Size firstrightitemsz)
{
+ /*
+ * Account for the new item on whichever side it is to be put.
+ */
if (newitemonleft)
leftfree -= (int) state->newitemsz;
else
*/
if (state->non_leaf)
rightfree += (int) firstrightitemsz -
- (int) (sizeof(BTItemData) + sizeof(ItemIdData));
+ (int) (MAXALIGN(sizeof(BTItemData)) + sizeof(ItemIdData));
/*
* If feasible split point, remember best delta.
*/
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtutils.c,v 1.38 2000/07/21 06:42:33 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtutils.c,v 1.39 2000/07/21 19:21:00 tgl Exp $
*
*-------------------------------------------------------------------------
*/
pfree(skey);
}
+/*
+ * free a retracement stack made by _bt_search.
+ */
void
_bt_freestack(BTStack stack)
{
}
/*
+ * Construct a BTItem from a plain IndexTuple.
+ *
+ * This is now useless code, since a BTItem *is* an index tuple with
+ * no extra stuff. We hang onto it for the moment to preserve the
+ * notational distinction, in case we want to add some extra stuff
+ * again someday.
+ */
+BTItem
+_bt_formitem(IndexTuple itup)
+{
+ int nbytes_btitem;
+ BTItem btitem;
+ Size tuplen;
+ extern Oid newoid();
+
+ /* make a copy of the index tuple with room for extra stuff */
+ tuplen = IndexTupleSize(itup);
+ nbytes_btitem = tuplen + (sizeof(BTItemData) - sizeof(IndexTupleData));
+
+ btitem = (BTItem) palloc(nbytes_btitem);
+ memcpy((char *) &(btitem->bti_itup), (char *) itup, tuplen);
+
+ return btitem;
+}
+
+/*
* _bt_orderkeys() -- Put keys in a sensible order for conjunctive quals.
*
* The order of the keys in the qual match the ordering imposed by
- * the index. This routine only needs to be called if there are
- * more than one qual clauses using this index.
+ * the index. This routine only needs to be called if there is
+ * more than one qual clause using this index.
*/
void
_bt_orderkeys(Relation relation, BTScanOpaque so)
if (i == numberOfKeys || cur->sk_attno != attno)
{
if (cur->sk_attno != attno + 1 && i < numberOfKeys)
- elog(ERROR, "_bt_orderkeys: key(s) for attribute %d missed", attno + 1);
+ elog(ERROR, "_bt_orderkeys: key(s) for attribute %d missed",
+ attno + 1);
underEqualStrategy = (!equalStrategyEnd);
pfree(xform);
}
-BTItem
-_bt_formitem(IndexTuple itup)
-{
- int nbytes_btitem;
- BTItem btitem;
- Size tuplen;
- extern Oid newoid();
-
- /* make a copy of the index tuple with room for the sequence number */
- tuplen = IndexTupleSize(itup);
- nbytes_btitem = tuplen + (sizeof(BTItemData) - sizeof(IndexTupleData));
-
- btitem = (BTItem) palloc(nbytes_btitem);
- memcpy((char *) &(btitem->bti_itup), (char *) itup, tuplen);
-
- return btitem;
-}
-
+/*
+ * Test whether an indextuple satisfies all the scankey conditions
+ *
+ * If not ("false" return), the number of conditions satisfied is
+ * returned in *keysok. Given proper ordering of the scankey conditions,
+ * we can use this to determine whether it's worth continuing the scan.
+ * See _bt_orderkeys().
+ *
+ * HACK: *keysok == (Size) -1 means we stopped evaluating because we found
+ * a NULL value in the index tuple. It's not quite clear to me why this
+ * case has to be treated specially --- tgl 7/00.
+ */
bool
_bt_checkkeys(IndexScanDesc scan, IndexTuple tuple, Size *keysok)
{
if (DatumGetBool(test) == !!(key[0].sk_flags & SK_NEGATE))
return false;
- keysz -= 1;
- key++;
(*keysok)++;
+ key++;
+ keysz--;
}
return true;
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