BTScanInsert itup_key)
{
TupleDesc itupdesc = RelationGetDescr(rel);
- int16 natts = IndexRelationGetNumberOfAttributes(rel);
int16 nkeyatts = IndexRelationGetNumberOfKeyAttributes(rel);
int keepnatts;
IndexTuple pivot;
+ IndexTuple tidpivot;
ItemPointer pivotheaptid;
Size newsize;
keepnatts = nkeyatts + 1;
#endif
- if (keepnatts <= natts)
- {
- IndexTuple tidpivot;
-
- pivot = index_truncate_tuple(itupdesc, firstright,
- Min(keepnatts, nkeyatts));
-
- if (BTreeTupleIsPosting(pivot))
- {
- /*
- * index_truncate_tuple() just returns a straight copy of
- * firstright when it has no key attributes to truncate. We need
- * to truncate away the posting list ourselves.
- */
- Assert(keepnatts == nkeyatts);
- Assert(natts == nkeyatts);
- pivot->t_info &= ~INDEX_SIZE_MASK;
- pivot->t_info |= MAXALIGN(BTreeTupleGetPostingOffset(firstright));
- }
-
- /*
- * If there is a distinguishing key attribute within new pivot tuple,
- * there is no need to add an explicit heap TID attribute
- */
- if (keepnatts <= nkeyatts)
- {
- BTreeTupleSetNAtts(pivot, keepnatts);
- return pivot;
- }
+ pivot = index_truncate_tuple(itupdesc, firstright,
+ Min(keepnatts, nkeyatts));
- /*
- * Only truncation of non-key attributes was possible, since key
- * attributes are all equal. It's necessary to add a heap TID
- * attribute to the new pivot tuple.
- */
- Assert(natts != nkeyatts);
- Assert(!BTreeTupleIsPosting(lastleft) &&
- !BTreeTupleIsPosting(firstright));
- newsize = IndexTupleSize(pivot) + MAXALIGN(sizeof(ItemPointerData));
- tidpivot = palloc0(newsize);
- memcpy(tidpivot, pivot, IndexTupleSize(pivot));
- /* cannot leak memory here */
- pfree(pivot);
- pivot = tidpivot;
- }
- else
+ if (BTreeTupleIsPosting(pivot))
{
/*
- * No truncation was possible, since key attributes are all equal.
- * It's necessary to add a heap TID attribute to the new pivot tuple.
- *
- * This path is only taken when rel is not an INCLUDE index. It
- * avoids a second palloc0() by avoiding the index_truncate_tuple()
- * call completely.
+ * index_truncate_tuple() just returns a straight copy of firstright
+ * when it has no attributes to truncate. When that happens, we may
+ * need to truncate away a posting list here instead.
*/
- Assert(natts == nkeyatts);
- newsize = IndexTupleSize(firstright) + MAXALIGN(sizeof(ItemPointerData));
- pivot = palloc0(newsize);
- memcpy(pivot, firstright, IndexTupleSize(firstright));
+ Assert(keepnatts == nkeyatts || keepnatts == nkeyatts + 1);
+ Assert(IndexRelationGetNumberOfAttributes(rel) == nkeyatts);
+ pivot->t_info &= ~INDEX_SIZE_MASK;
+ pivot->t_info |= MAXALIGN(BTreeTupleGetPostingOffset(firstright));
+ }
- if (BTreeTupleIsPosting(firstright))
- {
- /*
- * New pivot tuple was copied from firstright, which happens to be
- * a posting list tuple. We will have to include the max lastleft
- * heap TID in the final pivot tuple, but we can remove the
- * posting list now. (Pivot tuples should never contain a posting
- * list.)
- */
- newsize = MAXALIGN(BTreeTupleGetPostingOffset(firstright)) +
- MAXALIGN(sizeof(ItemPointerData));
- }
+ /*
+ * If there is a distinguishing key attribute within pivot tuple, we're
+ * done
+ */
+ if (keepnatts <= nkeyatts)
+ {
+ BTreeTupleSetNAtts(pivot, keepnatts);
+ return pivot;
}
/*
- * We have to use heap TID as a unique-ifier in the new pivot tuple, since
- * no non-TID key attribute in the right item readily distinguishes the
- * right side of the split from the left side. Use enlarged space that
- * holds a copy of first right tuple; place a heap TID value within the
- * extra space that remains at the end.
+ * We have to store a heap TID in the new pivot tuple, since no non-TID
+ * key attribute value in firstright distinguishes the right side of the
+ * split from the left side. nbtree conceptualizes this case as an
+ * inability to truncate away any key attributes, since heap TID is
+ * treated as just another key attribute (despite lacking a pg_attribute
+ * entry).
*
- * nbtree conceptualizes this case as an inability to truncate away any
- * key attribute. We must use an alternative representation of heap TID
- * within pivots because heap TID is only treated as an attribute within
- * nbtree (e.g., there is no pg_attribute entry).
+ * Use enlarged space that holds a copy of pivot. We need the extra space
+ * to store a heap TID at the end (using the special pivot tuple
+ * representation). Note that the original pivot already has firstright's
+ * possible posting list/non-key attribute values removed at this point.
*/
- Assert(itup_key->heapkeyspace);
- pivot->t_info &= ~INDEX_SIZE_MASK;
- pivot->t_info |= newsize;
+ newsize = MAXALIGN(IndexTupleSize(pivot)) + MAXALIGN(sizeof(ItemPointerData));
+ tidpivot = palloc0(newsize);
+ memcpy(tidpivot, pivot, MAXALIGN(IndexTupleSize(pivot)));
+ /* Cannot leak memory here */
+ pfree(pivot);
+
+ /* Store heap TID in enlarged pivot tuple */
+ tidpivot->t_info &= ~INDEX_SIZE_MASK;
+ tidpivot->t_info |= newsize;
+ BTreeTupleSetNAtts(tidpivot, nkeyatts);
+ BTreeTupleSetAltHeapTID(tidpivot);
/*
* Lehman & Yao use lastleft as the leaf high key in all cases, but don't
* TID. (This is also the closest value to negative infinity that's
* legally usable.)
*/
- pivotheaptid = (ItemPointer) ((char *) pivot + newsize -
+ pivotheaptid = (ItemPointer) ((char *) tidpivot + newsize -
sizeof(ItemPointerData));
ItemPointerCopy(BTreeTupleGetMaxHeapTID(lastleft), pivotheaptid);
/*
+ * We're done. Assert() that heap TID invariants hold before returning.
+ *
* Lehman and Yao require that the downlink to the right page, which is to
* be inserted into the parent page in the second phase of a page split be
* a strict lower bound on items on the right page, and a non-strict upper
BTreeTupleGetHeapTID(firstright)) < 0);
#endif
- BTreeTupleSetNAtts(pivot, nkeyatts);
- BTreeTupleSetAltHeapTID(pivot);
-
- return pivot;
+ return tidpivot;
}
/*
projects / users / c2main / postgres.git / commitdiff