materialized views: Add view class

This patch adds the view class, which will contains functions related
to populating a view, either from the base table's write path or from
the view building mechanism which copies over already existing data in
the base table.

Signed-off-by: Duarte Nunes <duarte@scylladb.com>

database.cc

@@ -3446,3 +3446,26 @@ void column_family::set_schema(schema_ptr s) {
     set_compaction_strategy(_schema->compaction_strategy());
     trigger_compaction();
 }
+
+void column_family::update_view_schemas() {
+    _view_schemas = boost::copy_range<std::vector<view_ptr>>(_views | boost::adaptors::map_values | boost::adaptors::transformed([] (auto&& s) {
+        return view_ptr(s.schema());
+    }));
+}
+
+void column_family::add_or_update_view(view_ptr v) {
+    auto e = _views.emplace(v->cf_name(), v);
+    if (!e.second) {
+        e.first->second.update(v);
+    }
+    update_view_schemas();
+}
+
+void column_family::remove_view(view_ptr v) {
+    _views.erase(v->cf_name());
+    update_view_schemas();
+}
+
+const std::vector<view_ptr>& column_family::views() const {
+    return _view_schemas;
+}

database.hh

@@ -74,6 +74,7 @@
 #include <seastar/core/shared_future.hh>
 #include "tracing/trace_state.hh"
 #include <boost/intrusive/parent_from_member.hpp>
+#include "db/view/view.hh"
 
 class frozen_mutation;
 class reconcilable_result;
@@ -510,6 +511,8 @@ private:
     // Last but not least, we seldom need to guarantee any ordering here: as long
     // as all data is waited for, we're good.
     seastar::gate _streaming_flush_gate;
+    std::unordered_map<sstring, db::view::view> _views;
+    std::vector<view_ptr> _view_schemas;
 private:
     void update_stats_for_new_sstable(uint64_t disk_space_used_by_sstable);
     void add_sstable(sstables::sstable&& sstable);
@@ -796,7 +799,13 @@ public:
             }
         });
     }
+
+    void add_or_update_view(view_ptr v);
+    void remove_view(view_ptr v);
+    const std::vector<view_ptr>& views() const;
 private:
+    void update_view_schemas();
+
     // One does not need to wait on this future if all we are interested in, is
     // initiating the write.  The writes initiated here will eventually
     // complete, and the seastar::gate below will make sure they are all

db/view/view.hh

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2016 ScyllaDB
+ */
+
+/*
+ * This file is part of Scylla.
+ *
+ * Scylla is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Scylla is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Scylla.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "schema.hh"
+
+namespace db {
+
+namespace view {
+
+class view final {
+    view_ptr _schema;
+public:
+    view(view_ptr schema)
+            : _schema(schema)
+    { }
+
+    view_ptr schema() const {
+        return _schema;
+    }
+
+    void update(view_ptr new_schema) {
+        _schema = new_schema;
+    }
+};
+
+}
+
+}