Warn user about using SimpleStrategy with Multi DC deployment

If the user creates a keyspace with the 'SimpleStrategy' replication class
in a multi-datacenter environment, they will receive a warning in the CQL shell
and in the server logs.
Resolves #4481.

Signed-off-by: Kamil Braun <kbraun@scylladb.com>

cql3/statements/create_keyspace_statement.cc

@@ -43,6 +43,8 @@
 #include "prepared_statement.hh"
 #include "database.hh"
 #include "service/migration_manager.hh"
+#include "service/storage_service.hh"
+#include "transport/messages/result_message.hh"
 
 #include <regex>
 
@@ -52,6 +54,8 @@ namespace cql3 {
 
 namespace statements {
 
+logging::logger create_keyspace_statement::_logger("create_keyspace");
+
 create_keyspace_statement::create_keyspace_statement(const sstring& name, shared_ptr<ks_prop_defs> attrs, bool if_not_exists)
     : _name{name}
     , _attrs{attrs}
@@ -139,6 +143,24 @@ future<> cql3::statements::create_keyspace_statement::grant_permissions_to_creat
     });
 }
 
+future<::shared_ptr<messages::result_message>>
+create_keyspace_statement::execute(service::storage_proxy& proxy, service::query_state& state, const query_options& options) {
+    return schema_altering_statement::execute(proxy, state, options).then([this] (::shared_ptr<messages::result_message> msg) {
+        bool multidc = service::get_local_storage_service().get_token_metadata().
+                                get_topology().get_datacenter_endpoints().size() > 1;
+        bool simple = _attrs->get_replication_strategy_class() == "SimpleStrategy";
+
+        if (multidc && simple) {
+            static const auto warning = "Using SimpleStrategy in a multi-datacenter environment is not recommended.";
+
+            msg->add_warning(warning);
+            _logger.warn(warning);
+        }
+
+        return msg;
+    });
+}
+
 }
 
 }

cql3/statements/create_keyspace_statement.hh

@@ -44,6 +44,7 @@
 #include "cql3/statements/schema_altering_statement.hh"
 #include "cql3/statements/ks_prop_defs.hh"
 #include "transport/event.hh"
+#include "log.hh"
 
 #include <seastar/core/shared_ptr.hh>
 
@@ -54,6 +55,8 @@ namespace statements {
 /** A <code>CREATE KEYSPACE</code> statement parsed from a CQL query. */
 class create_keyspace_statement : public schema_altering_statement {
 private:
+    static logging::logger _logger;
+
     sstring _name;
     shared_ptr<ks_prop_defs> _attrs;
     bool _if_not_exists;
@@ -86,6 +89,9 @@ public:
     virtual std::unique_ptr<prepared> prepare(database& db, cql_stats& stats) override;
 
     virtual future<> grant_permissions_to_creator(const service::client_state&) override;
+
+    virtual future<::shared_ptr<messages::result_message>>
+    execute(service::storage_proxy& proxy, service::query_state& state, const query_options& options) override;
 };
 
 }