clustering_range_walker: fix false discontiguity detected after a sta…

…tic row

clustering_range_walker detects when we jump from one row range to another. When
a static row is included in the query, the constructor sets up the first before/after
bounds to be exactly that static row. That creates an artificial range crossing if
the first clustering range is contiguous with the static row.

This can cause the index to be consulted needlessly if we happen to fall back
to sstable_mutation_reader after reading the static row.

A unit test is added.

Ref #7883.

clustering_ranges_walker.hh

@@ -65,6 +65,11 @@ private:
                 _current_start = position_in_partition_view::for_range_start(_current_range.front());
                 _current_end = position_in_partition_view::for_range_end(_current_range.front());
             }
+        } else {
+             // If the first range is contiguous with the static row, then advance _current_end as much as we can
+             if (_current_range && !_current_range.front().start()) {
+                 _current_end = position_in_partition_view::for_range_end(_current_range.front());
+             }
         }
     }
 

test/boost/clustering_ranges_walker_test.cc

@@ -289,3 +289,29 @@ SEASTAR_TEST_CASE(test_range_overlap) {
 
     return make_ready_future<>();
 }
+
+SEASTAR_TEST_CASE(verify_static_row_can_be_contiguous_with_a_clustering_range_that_is_open_in_front) {
+    simple_schema s;
+    auto keys = s.make_ckeys(10);
+    auto range1 = query::clustering_range::make_ending_with({keys[2], false});
+    auto ranges = query::clustering_row_ranges({range1});
+    auto walker = clustering_ranges_walker(*s.schema(), ranges);
+    auto cc = walker.lower_bound_change_counter();
+    walker.advance_to(position_in_partition::for_key(keys[1]));
+    BOOST_REQUIRE_EQUAL(cc, walker.lower_bound_change_counter());
+    walker.advance_to(position_in_partition::for_key(keys[3]));
+    BOOST_REQUIRE_NE(cc, walker.lower_bound_change_counter());
+    return make_ready_future<>();
+}
+
+SEASTAR_TEST_CASE(verify_static_row_can_be_contiguous_with_a_clustering_range_negative_tests) {
+    simple_schema s;
+    auto keys = s.make_ckeys(10);
+    auto range1 = query::clustering_range::make({keys[2], false}, {keys[4], false});
+    auto ranges = query::clustering_row_ranges({range1});
+    auto walker = clustering_ranges_walker(*s.schema(), ranges);
+    auto cc = walker.lower_bound_change_counter();
+    walker.advance_to(position_in_partition::for_key(keys[3]));
+    BOOST_REQUIRE_NE(cc, walker.lower_bound_change_counter());
+    return make_ready_future<>();
+}