abstract_replication_strategy: add has_uniform_natural_endpoints

So that using calaculate_natural_endpoints can be optimized
for strategies that return the same endpoints for all tokens,
namely everywhere_replication_strategy and local_strategy.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>

locator/abstract_replication_strategy.hh

@@ -78,6 +78,10 @@ public:
         const replication_strategy_config_options& config_options,
         replication_strategy_type my_type);
 
+    // Evaluates to true iff calculate_natural_endpoints
+    // returns different results for different tokens.
+    virtual bool natural_endpoints_depend_on_token() const noexcept { return true; }
+
     // The returned vector has size O(number of normal token owners), which is O(number of nodes in the cluster).
     // Note: it is not guaranteed that the function will actually yield. If the complexity of a particular implementation
     // is small, that implementation may not yield since by itself it won't cause a reactor stall (assuming practical

locator/everywhere_replication_strategy.hh

@@ -18,6 +18,8 @@ class everywhere_replication_strategy : public abstract_replication_strategy {
 public:
     everywhere_replication_strategy(const replication_strategy_config_options& config_options);
 
+    virtual bool natural_endpoints_depend_on_token() const noexcept override { return false; }
+
     virtual future<endpoint_set> calculate_natural_endpoints(const token& search_token, const token_metadata& tm) const override;
 
     virtual void validate_options() const override { /* noop */ }

locator/local_strategy.hh

@@ -27,6 +27,8 @@ public:
     virtual ~local_strategy() {};
     virtual size_t get_replication_factor(const token_metadata&) const override;
 
+    virtual bool natural_endpoints_depend_on_token() const noexcept override { return false; }
+
     virtual future<endpoint_set> calculate_natural_endpoints(const token& search_token, const token_metadata& tm) const override;
 
     virtual void validate_options() const override;