memgraph/src/database/graph_db.hpp

#pragma once

#include <thread>

#include "cppitertools/filter.hpp"
#include "cppitertools/imap.hpp"

#include "data_structures/concurrent/concurrent_set.hpp"
#include "data_structures/concurrent/skiplist.hpp"
#include "database/graph_db_datatypes.hpp"
#include "database/indexes/key_index.hpp"
#include "database/indexes/label_property_index.hpp"
#include "durability/snapshooter.hpp"
#include "mvcc/version_list.hpp"
#include "storage/deferred_deleter.hpp"
#include "storage/edge.hpp"
#include "storage/garbage_collector.hpp"
#include "storage/unique_object_store.hpp"
#include "storage/vertex.hpp"
#include "transactions/engine.hpp"
#include "utils/scheduler.hpp"

namespace fs = std::experimental::filesystem;

// TODO: Maybe split this in another layer between Db and Dbms. Where the new
// layer would hold SnapshotEngine and his kind of concept objects. Some
// guidelines would be: retain objects which are necessary to implement querys
// in Db, the rest can be moved to the new layer.
/**
 * Main class which represents Database concept in code.
 * This class is essentially a data structure. It exposes
 * all the data publicly, and should therefore not be directly
 * exposed to client functions. The GraphDbAccessor is used for that.
 */
class GraphDb {
 public:
  /**
   * Construct database with a custom name.
   *
   * @param name database name
   * @param import_snapshot will in constructor import latest snapshot
   *                        into the db.
   */
  GraphDb(const std::string &name, const fs::path &snapshot_db_dir);
  /**
   * @brief - Destruct database object. Delete all vertices and edges and free
   * all deferred deleters.
   */
  ~GraphDb();

  /**
   * Database object can't be copied.
   */
  GraphDb(const GraphDb &db) = delete;
  GraphDb(GraphDb &&other) = default;
  GraphDb &operator=(const GraphDb &other) = default;
  GraphDb &operator=(GraphDb &&other) = default;

  /**
   * Starts database snapshooting.
   */
  void StartSnapshooting();

  /**
   * Recovers database from a snapshot file and starts snapshooting.
   * @param snapshot_db path to snapshot folder
   */
  void RecoverDatabase(const fs::path &snapshot_db_path);

  /**
   * Collects garbage.
   */
  void CollectGarbage();

  /** transaction engine related to this database */
  tx::Engine tx_engine_;

  // database name
  const std::string name_;

  // main storage for the graph
  SkipList<mvcc::VersionList<Vertex> *> vertices_;
  SkipList<mvcc::VersionList<Edge> *> edges_;

  // Garbage collectors
  GarbageCollector<Vertex> gc_vertices_;
  GarbageCollector<Edge> gc_edges_;

  // Deleters for not relevant records
  DeferredDeleter<Vertex> vertex_record_deleter_;
  DeferredDeleter<Edge> edge_record_deleter_;

  // Deleters for not relevant version_lists
  DeferredDeleter<mvcc::VersionList<Vertex>> vertex_version_list_deleter_;
  DeferredDeleter<mvcc::VersionList<Edge>> edge_version_list_deleter_;

  // unique object stores
  // TODO this should be also garbage collected
  ConcurrentSet<std::string> labels_;
  ConcurrentSet<std::string> edge_types_;
  ConcurrentSet<std::string> properties_;

  // indexes
  KeyIndex<GraphDbTypes::Label, Vertex> labels_index_;
  KeyIndex<GraphDbTypes::EdgeType, Edge> edge_types_index_;
  LabelPropertyIndex label_property_index_;

  // Flag indicating if index building is in progress. Memgraph does not support
  // concurrent index builds on the same database (transaction engine), so we
  // reject index builds if there is one in progress. See
  // GraphDbAccessor::BuildIndex.
  std::atomic<bool> index_build_in_progress_{false};

  // snapshooter
  Snapshooter snapshooter_;

  // Schedulers
  Scheduler<std::mutex> gc_scheduler_;
  Scheduler<std::mutex> snapshot_creator_;
  // Periodically wakes up and hints to transactions that are running for a long
  // time to stop their execution.
  Scheduler<std::mutex> transaction_killer_;
};