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

On Thu, Aug 29, 2019 at 10:10 PM Peter Geoghegan <pg(at)bowt(dot)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