Re: [HACKERS] [WIP] Effective storage of duplicates in B-tree index.

On Thu, Aug 29, 2019 at 10:10 PM Peter Geoghegan <pg@bowt.ie> wrote:
> I see some Valgrind errors on v9, all of which look like the following
> two sample errors I go into below.

I've found a fix for these Valgrind issues. It's a matter of making
sure that _bt_truncate() sizes new pivot tuples properly, which is
quite subtle:

--- a/src/backend/access/nbtree/nbtutils.c
+++ b/src/backend/access/nbtree/nbtutils.c
@@ -2155,8 +2155,11 @@ _bt_truncate(Relation rel, IndexTuple lastleft,
IndexTuple firstright,
         {
             BTreeTupleClearBtIsPosting(pivot);
             BTreeTupleSetNAtts(pivot, keepnatts);
-            pivot->t_info &= ~INDEX_SIZE_MASK;
-            pivot->t_info |= BTreeTupleGetPostingOffset(firstright);
+            if (keepnatts == natts)
+            {
+                pivot->t_info &= ~INDEX_SIZE_MASK;
+                pivot->t_info |=
MAXALIGN(BTreeTupleGetPostingOffset(firstright));
+            }
         }

I'm varying how the new pivot tuple is sized here according to whether
or not index_truncate_tuple() just does a CopyIndexTuple(). This very
slightly changes the behavior of the nbtsplitloc.c stuff, but that's
not a concern for me.

I will post a patch with this and other tweaks next week.

--
Peter Geoghegan