nbtree: Demote minus infinity "can't happen" error.

Only a very basic logic bug in a _bt_insertonpg() caller could lead to a
violation of this invariant.  Besides, any newitemoff used for an
internal page is sanitized using other "can't happen" errors in
_bt_getstackbuf() or its callers, before _bt_insertonpg() even gets
called.

Also, move the error/assertion from the insert-without-split path of
_bt_insertonpg() to the top of the same function.  There is no reason
why this invariant only applies to insertions that happen to not result
in a page split; cover every insertion.  The assertion naturally belongs
next to the existing generic assertions that document relatively
high-level invariants for the item being inserted.

diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index 03b7e45293a3e5959de7322f2df591a0efea9adc..fb814ef722bcdb203cf62616f015daf0348388d1 100644 (file)
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -1082,6 +1082,14 @@ _bt_insertonpg(Relation rel,
           IndexRelationGetNumberOfKeyAttributes(rel));
    Assert(!BTreeTupleIsPosting(itup));
 
+   /*
+    * Every internal page should have exactly one negative infinity item at
+    * all times.  Only _bt_split() and _bt_newroot() should add items that
+    * become negative infinity items through truncation, since they're the
+    * only routines that allocate new internal pages.
+    */
+   Assert(P_ISLEAF(lpageop) || newitemoff > P_FIRSTDATAKEY(lpageop));
+
    /* The caller should've finished any incomplete splits already. */
    if (P_INCOMPLETE_SPLIT(lpageop))
        elog(ERROR, "cannot insert to incompletely split page %u",
@@ -1212,18 +1220,6 @@ _bt_insertonpg(Relation rel,
            }
        }
 
-       /*
-        * Every internal page should have exactly one negative infinity item
-        * at all times.  Only _bt_split() and _bt_newroot() should add items
-        * that become negative infinity items through truncation, since
-        * they're the only routines that allocate new internal pages.  Do not
-        * allow a retail insertion of a new item at the negative infinity
-        * offset.
-        */
-       if (!P_ISLEAF(lpageop) && newitemoff == P_FIRSTDATAKEY(lpageop))
-           elog(ERROR, "cannot insert second negative infinity item in block %u of index \"%s\"",
-                itup_blkno, RelationGetRelationName(rel));
-
        /* Do the update.  No ereport(ERROR) until changes are logged */
        START_CRIT_SECTION();