query: add full_slice

query::full_slice is a partiton slice which has full clustering row
ranges for all partition keys and no per-partition row limit.
Options and columns are not set.

It is used as a helper object in cases when a reference to
partition_slice is needed but the user code needs just all data there is
(an example of such case would be sstable compaction).

Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>

query-request.hh

@@ -157,6 +157,10 @@ public:
 
 constexpr auto max_partitions = std::numeric_limits<uint32_t>::max();
 
+// This is a partition slice which a full clustering row range and maximum
+// per-partition row limit. No options or columns are set.
+extern const query::partition_slice full_slice;
+
 // Full specification of a query to the database.
 // Intended for passing across replicas.
 // Can be accessed across cores.

query.cc

@@ -34,6 +34,8 @@ namespace query {
 
 const partition_range full_partition_range = partition_range::make_open_ended_both_sides();
 
+const query::partition_slice full_slice = query::partition_slice({ query::clustering_range::make_open_ended_both_sides() }, { }, { }, { });
+
 std::ostream& operator<<(std::ostream& out, const specific_ranges& s);
 
 std::ostream& operator<<(std::ostream& out, const partition_slice& ps) {