Re: Optimizing nbtree ScalarArrayOp execution, allowing multi-column ordered scans, skip scan

Coverity pointed out something that looks like a potentially live
problem in 5bf748b86:

/srv/coverity/git/pgsql-git/postgresql/src/backend/access/nbtree/nbtutils.c: 2950 in _bt_preprocess_keys()
2944                              * need to make sure that we don't throw away an array
2945                              * scan key.  _bt_compare_scankey_args expects us to
2946                              * always keep arrays (and discard non-arrays).
2947                              */
2948                             Assert(j == (BTEqualStrategyNumber - 1));
2949                             Assert(xform[j].skey->sk_flags & SK_SEARCHARRAY);
>>>     CID 1596256:  Null pointer dereferences  (FORWARD_NULL)
>>>     Dereferencing null pointer "array".
2950                             Assert(xform[j].ikey == array->scan_key);
2951                             Assert(!(cur->sk_flags & SK_SEARCHARRAY));
2952                         }
2953                     }
2954                     else if (j == (BTEqualStrategyNumber - 1))

Above this there is an assertion

                    Assert(!array || array->num_elems > 0);

which certainly makes it look like array->scan_key could be
a null-pointer dereference.

            regards, tom lane