Re: WIP: Covering + unique indexes.

On Mon, Aug 15, 2016 at 8:15 PM, Anastasia Lubennikova
<a(dot)lubennikova(at)postgrespro(dot)ru> wrote:
@@ -590,7 +622,14 @@ _bt_buildadd(BTWriteState *wstate, BTPageState
*state, IndexTuple itup)
if (last_off == P_HIKEY)
{
Assert(state->btps_minkey == NULL);
- state->btps_minkey = CopyIndexTuple(itup);
+ /*
+ * Truncate the tuple that we're going to insert
+ * into the parent page as a downlink
+ */

+ if (indnkeyatts != indnatts && P_ISLEAF(pageop))
+ state->btps_minkey = index_truncate_tuple(wstate->index, itup);
+ else
+ state->btps_minkey = CopyIndexTuple(itup);

It seems that above code always ensure that for leaf pages, high key
is a truncated tuple. What is less clear is if that is true, why you
need to re-ensure it again for the old page in below code:

@@ -510,6 +513,8 @@ _bt_buildadd(BTWriteState *wstate, BTPageState
*state, IndexTuple itup)
{
..
+ if (indnkeyatts != indnatts && P_ISLEAF(opageop))
+ {
+ /*
+ * It's essential to truncate High key here.
+ * The purpose is not just to save more space on this particular page,
+ * but to keep whole b-tree structure consistent. Subsequent insertions
+ * assume that hikey is already truncated, and so they should not
+ * worry about it, when copying the high key into the parent page
+ * as a downlink.
+ * NOTE It is not crutial for reliability in present,
+ * but maybe it will be that in the future.
+ */
+ keytup = index_truncate_tuple(wstate->index, oitup);
+
+ /* delete "wrong" high key, insert keytup as P_HIKEY. */
+ PageIndexTupleDelete(opage, P_HIKEY);
+
+ if (!_bt_pgaddtup(opage, IndexTupleSize(keytup), keytup, P_HIKEY))
+ elog(ERROR, "failed to rewrite compressed item in index \"%s\"",
+ RelationGetRelationName(wstate->index));
+ }
+
..
..

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com