ClickHouse/src/Interpreters/DatabaseCatalog.h

#pragma once

#include <Core/UUID.h>
#include <Interpreters/Context_fwd.h>
#include <Interpreters/StorageID.h>
#include <Databases/TablesDependencyGraph.h>
#include <Parsers/IAST_fwd.h>
#include <Storages/IStorage_fwd.h>
#include "Common/NamePrompter.h"
#include <Common/SharedMutex.h>
#include "Storages/IStorage.h"
#include "Databases/IDatabase.h"

#include <boost/noncopyable.hpp>
#include <Poco/Logger.h>

#include <array>
#include <condition_variable>
#include <list>
#include <map>
#include <memory>
#include <mutex>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <filesystem>

namespace fs = std::filesystem;

namespace DB
{

class IDatabase;
class Exception;
class ColumnsDescription;
struct ConstraintsDescription;
class IDisk;

using DatabasePtr = std::shared_ptr<IDatabase>;
using DatabaseAndTable = std::pair<DatabasePtr, StoragePtr>;
using Databases = std::map<String, std::shared_ptr<IDatabase>>;
using DiskPtr = std::shared_ptr<IDisk>;
using TableNamesSet = std::unordered_set<QualifiedTableName>;

/// Allows executing DDL query only in one thread.
/// Puts an element into the map, locks tables's mutex, counts how much threads run parallel query on the table,
/// when counter is 0 erases element in the destructor.
/// If the element already exists in the map, waits when ddl query will be finished in other thread.
class DDLGuard
{
public:
    struct Entry
    {
        std::unique_ptr<std::mutex> mutex;
        UInt32 counter;
    };

    /// Element name -> (mutex, counter).
    /// NOTE: using std::map here (and not std::unordered_map) to avoid iterator invalidation on insertion.
    using Map = std::map<String, Entry>;

    DDLGuard(
        Map & map_,
        SharedMutex & db_mutex_,
        std::unique_lock<std::mutex> guards_lock_,
        const String & elem,
        const String & database_name);
    ~DDLGuard();

    /// Unlocks table name, keeps holding read lock for database name
    void releaseTableLock() noexcept;

private:
    Map & map;
    SharedMutex & db_mutex;
    Map::iterator it;
    std::unique_lock<std::mutex> guards_lock;
    std::unique_lock<std::mutex> table_lock;
    bool table_lock_removed = false;
    bool is_database_guard = false;
};

using DDLGuardPtr = std::unique_ptr<DDLGuard>;

class FutureSetFromSubquery;
using FutureSetFromSubqueryPtr = std::shared_ptr<FutureSetFromSubquery>;

/// Creates temporary table in `_temporary_and_external_tables` with randomly generated unique StorageID.
/// Such table can be accessed from everywhere by its ID.
/// Removes the table from database on destruction.
/// TemporaryTableHolder object can be attached to a query or session Context, so table will be accessible through the context.
struct TemporaryTableHolder : boost::noncopyable, WithContext
{
    using Creator = std::function<StoragePtr (const StorageID &)>;

    TemporaryTableHolder(ContextPtr context, const Creator & creator, const ASTPtr & query = {});

    /// Creates temporary table with Engine=Memory
    TemporaryTableHolder(
        ContextPtr context,
        const ColumnsDescription & columns,
        const ConstraintsDescription & constraints,
        const ASTPtr & query = {},
        bool create_for_global_subquery = false);

    TemporaryTableHolder(TemporaryTableHolder && rhs) noexcept;
    TemporaryTableHolder & operator=(TemporaryTableHolder && rhs) noexcept;

    ~TemporaryTableHolder();

    StorageID getGlobalTableID() const;

    StoragePtr getTable() const;

    operator bool () const { return id != UUIDHelpers::Nil; } /// NOLINT

    IDatabase * temporary_tables = nullptr;
    UUID id = UUIDHelpers::Nil;
    FutureSetFromSubqueryPtr future_set;
};

///TODO maybe remove shared_ptr from here?
using TemporaryTablesMapping = std::map<String, std::shared_ptr<TemporaryTableHolder>>;

class BackgroundSchedulePoolTaskHolder;

/// For some reason Context is required to get Storage from Database object
class DatabaseCatalog : boost::noncopyable, WithMutableContext
{
public:
    /// Names of predefined databases.
    static constexpr const char * TEMPORARY_DATABASE = "_temporary_and_external_tables";
    static constexpr const char * SYSTEM_DATABASE = "system";
    static constexpr const char * INFORMATION_SCHEMA = "information_schema";
    static constexpr const char * INFORMATION_SCHEMA_UPPERCASE = "INFORMATION_SCHEMA";

    /// Returns true if a passed name is one of the predefined databases' names.
    static bool isPredefinedDatabase(std::string_view database_name);

    static DatabaseCatalog & init(ContextMutablePtr global_context_);
    static DatabaseCatalog & instance();
    static void shutdown();

    void createBackgroundTasks();
    void initializeAndLoadTemporaryDatabase();
    void startupBackgroundTasks();
    void loadMarkedAsDroppedTables();

    /// Get an object that protects the table from concurrently executing multiple DDL operations.
    DDLGuardPtr getDDLGuard(const String & database, const String & table);
    /// Get an object that protects the database from concurrent DDL queries all tables in the database
    std::unique_lock<SharedMutex> getExclusiveDDLGuardForDatabase(const String & database);

    /// We need special synchronization between DROP/DETACH DATABASE and SYSTEM RESTART REPLICA
    /// because IStorage::flushAndPrepareForShutdown cannot be protected by DDLGuard (and a race with IStorage::startup is possible)
    std::unique_lock<SharedMutex> getLockForDropDatabase(const String & database);
    std::optional<std::shared_lock<SharedMutex>> tryGetLockForRestartReplica(const String & database);


    void assertDatabaseExists(const String & database_name) const;
    void assertDatabaseDoesntExist(const String & database_name) const;

    DatabasePtr getDatabaseForTemporaryTables() const;
    DatabasePtr getSystemDatabase() const;

    void attachDatabase(const String & database_name, const DatabasePtr & database);
    DatabasePtr detachDatabase(ContextPtr local_context, const String & database_name, bool drop = false, bool check_empty = true);
    void updateDatabaseName(const String & old_name, const String & new_name, const Strings & tables_in_database);

    /// database_name must be not empty
    DatabasePtr getDatabase(const String & database_name) const;
    DatabasePtr tryGetDatabase(const String & database_name) const;
    DatabasePtr getDatabase(const UUID & uuid) const;
    DatabasePtr tryGetDatabase(const UUID & uuid) const;
    bool isDatabaseExist(const String & database_name) const;
    Databases getDatabases() const;

    /// Same as getDatabase(const String & database_name), but if database_name is empty, current database of local_context is used
    DatabasePtr getDatabase(const String & database_name, ContextPtr local_context) const;

    /// For all of the following methods database_name in table_id must be not empty (even for temporary tables).
    void assertTableDoesntExist(const StorageID & table_id, ContextPtr context) const;
    bool isTableExist(const StorageID & table_id, ContextPtr context) const;
    bool isDictionaryExist(const StorageID & table_id) const;

    StoragePtr getTable(const StorageID & table_id, ContextPtr context) const;
    StoragePtr tryGetTable(const StorageID & table_id, ContextPtr context) const;
    DatabaseAndTable getDatabaseAndTable(const StorageID & table_id, ContextPtr context) const;
    DatabaseAndTable tryGetDatabaseAndTable(const StorageID & table_id, ContextPtr context) const;
    DatabaseAndTable getTableImpl(const StorageID & table_id,
                                  ContextPtr context,
                                  std::optional<Exception> * exception = nullptr) const;

    /// Returns true if a passed table_id refers to one of the predefined tables' names.
    /// All tables in the "system" database with System* table engine are predefined.
    /// Four views (tables, views, columns, schemata) in the "information_schema" database are predefined too.
    bool isPredefinedTable(const StorageID & table_id) const;

    /// View dependencies between a source table and its view.
    void addViewDependency(const StorageID & source_table_id, const StorageID & view_id);
    void removeViewDependency(const StorageID & source_table_id, const StorageID & view_id);
    std::vector<StorageID> getDependentViews(const StorageID & source_table_id) const;
    void updateViewDependency(const StorageID & old_source_table_id, const StorageID & old_view_id, const StorageID & new_source_table_id, const StorageID & new_view_id);

    /// If table has UUID, addUUIDMapping(...) must be called when table attached to some database
    /// removeUUIDMapping(...) must be called when it detached,
    /// and removeUUIDMappingFinally(...) must be called when table is dropped and its data removed from disk.
    /// Such tables can be accessed by persistent UUID instead of database and table name.
    void addUUIDMapping(const UUID & uuid, const DatabasePtr & database, const StoragePtr & table);
    void removeUUIDMapping(const UUID & uuid);
    void removeUUIDMappingFinally(const UUID & uuid);
    /// For moving table between databases
    void updateUUIDMapping(const UUID & uuid, DatabasePtr database, StoragePtr table);
    /// This method adds empty mapping (with database and storage equal to nullptr).
    /// It's required to "lock" some UUIDs and protect us from collision.
    /// Collisions of random 122-bit integers are very unlikely to happen,
    /// but we allow to explicitly specify UUID in CREATE query (in particular for testing).
    /// If some UUID was already added and we are trying to add it again,
    /// this method will throw an exception.
    void addUUIDMapping(const UUID & uuid);

    bool hasUUIDMapping(const UUID & uuid);

    static String getPathForUUID(const UUID & uuid);

    DatabaseAndTable tryGetByUUID(const UUID & uuid) const;

    String getPathForDroppedMetadata(const StorageID & table_id) const;
    String getPathForMetadata(const StorageID & table_id) const;
    void enqueueDroppedTableCleanup(StorageID table_id, StoragePtr table, String dropped_metadata_path, bool ignore_delay = false);
    void dequeueDroppedTableCleanup(StorageID table_id);

    void waitTableFinallyDropped(const UUID & uuid);

    /// Referential dependencies between tables: table "A" depends on table "B"
    /// if "B" is referenced in the definition of "A".
    /// Loading dependencies were used to check whether a table can be removed before we had those referential dependencies.
    /// Now we support this mode (see `check_table_referential_dependencies` in Setting.h) for compatibility.
    void addDependencies(const StorageID & table_id, const std::vector<StorageID> & new_referential_dependencies, const std::vector<StorageID> & new_loading_dependencies);
    void addDependencies(const QualifiedTableName & table_name, const TableNamesSet & new_referential_dependencies, const TableNamesSet & new_loading_dependencies);
    void addDependencies(const TablesDependencyGraph & new_referential_dependencies, const TablesDependencyGraph & new_loading_dependencies);
    std::pair<std::vector<StorageID>, std::vector<StorageID>> removeDependencies(const StorageID & table_id, bool check_referential_dependencies, bool check_loading_dependencies, bool is_drop_database = false);
    std::vector<StorageID> getReferentialDependencies(const StorageID & table_id) const;
    std::vector<StorageID> getReferentialDependents(const StorageID & table_id) const;
    std::vector<StorageID> getLoadingDependencies(const StorageID & table_id) const;
    std::vector<StorageID> getLoadingDependents(const StorageID & table_id) const;
    void updateDependencies(const StorageID & table_id, const TableNamesSet & new_referential_dependencies, const TableNamesSet & new_loading_dependencies);

    void checkTableCanBeRemovedOrRenamed(const StorageID & table_id, bool check_referential_dependencies, bool check_loading_dependencies, bool is_drop_database = false) const;


    struct TableMarkedAsDropped
    {
        StorageID table_id = StorageID::createEmpty();
        StoragePtr table;
        String metadata_path;
        time_t drop_time{};
    };
    using TablesMarkedAsDropped = std::list<TableMarkedAsDropped>;

    TablesMarkedAsDropped getTablesMarkedDropped()
    {
        std::lock_guard lock(tables_marked_dropped_mutex);
        return tables_marked_dropped;
    }

    void triggerReloadDisksTask(const Strings & new_added_disks);

private:
    // The global instance of database catalog. unique_ptr is to allow
    // deferred initialization. Thought I'd use std::optional, but I can't
    // make emplace(global_context_) compile with private constructor ¯\_(ツ)_/¯.
    static std::unique_ptr<DatabaseCatalog> database_catalog;

    explicit DatabaseCatalog(ContextMutablePtr global_context_);
    void assertDatabaseDoesntExistUnlocked(const String & database_name) const TSA_REQUIRES(databases_mutex);

    void shutdownImpl();

    void checkTableCanBeRemovedOrRenamedUnlocked(const StorageID & removing_table, bool check_referential_dependencies, bool check_loading_dependencies, bool is_drop_database) const TSA_REQUIRES(databases_mutex);

    struct UUIDToStorageMapPart
    {
        std::unordered_map<UUID, DatabaseAndTable> map TSA_GUARDED_BY(mutex);
        mutable std::mutex mutex;
    };

    static constexpr UInt64 bits_for_first_level = 4;
    using UUIDToStorageMap = std::array<UUIDToStorageMapPart, 1ull << bits_for_first_level>;

    static inline size_t getFirstLevelIdx(const UUID & uuid)
    {
        return UUIDHelpers::getHighBytes(uuid) >> (64 - bits_for_first_level);
    }

    void dropTableDataTask();
    void dropTableFinally(const TableMarkedAsDropped & table);

    void cleanupStoreDirectoryTask();
    bool maybeRemoveDirectory(const String & disk_name, const DiskPtr & disk, const String & unused_dir);

    void reloadDisksTask();

    static constexpr size_t reschedule_time_ms = 100;

    mutable std::mutex databases_mutex;

    Databases databases TSA_GUARDED_BY(databases_mutex);
    UUIDToStorageMap uuid_map;

    /// Referential dependencies between tables: table "A" depends on table "B"
    /// if the table "B" is referenced in the definition of the table "A".
    TablesDependencyGraph referential_dependencies TSA_GUARDED_BY(databases_mutex);

    /// Loading dependencies were used to check whether a table can be removed before we had referential dependencies.
    TablesDependencyGraph loading_dependencies TSA_GUARDED_BY(databases_mutex);

    /// View dependencies between a source table and its view.
    TablesDependencyGraph view_dependencies TSA_GUARDED_BY(databases_mutex);

    LoggerPtr log;

    std::atomic_bool is_shutting_down = false;

    /// Do not allow simultaneous execution of DDL requests on the same table.
    /// database name -> database guard -> (table name mutex, counter),
    /// counter: how many threads are running a query on the table at the same time
    /// For the duration of the operation, an element is placed here, and an object is returned,
    /// which deletes the element in the destructor when counter becomes zero.
    /// In case the element already exists, waits when query will be executed in other thread. See class DDLGuard below.
    struct DatabaseGuard
    {
        SharedMutex database_ddl_mutex;
        SharedMutex restart_replica_mutex;

        DDLGuard::Map table_guards;
    };
    DatabaseGuard & getDatabaseGuard(const String & database);

    using DDLGuards = std::map<String, DatabaseGuard>;
    DDLGuards ddl_guards TSA_GUARDED_BY(ddl_guards_mutex);
    /// If you capture mutex and ddl_guards_mutex, then you need to grab them strictly in this order.
    mutable std::mutex ddl_guards_mutex;

    TablesMarkedAsDropped tables_marked_dropped TSA_GUARDED_BY(tables_marked_dropped_mutex);
    TablesMarkedAsDropped::iterator first_async_drop_in_queue TSA_GUARDED_BY(tables_marked_dropped_mutex);
    std::unordered_set<UUID> tables_marked_dropped_ids TSA_GUARDED_BY(tables_marked_dropped_mutex);
    mutable std::mutex tables_marked_dropped_mutex;

    std::unique_ptr<BackgroundSchedulePoolTaskHolder> drop_task;
    static constexpr time_t default_drop_delay_sec = 8 * 60;
    time_t drop_delay_sec = default_drop_delay_sec;
    std::condition_variable wait_table_finally_dropped;

    std::unique_ptr<BackgroundSchedulePoolTaskHolder> cleanup_task;
    static constexpr time_t default_unused_dir_hide_timeout_sec = 60 * 60;              /// 1 hour
    time_t unused_dir_hide_timeout_sec = default_unused_dir_hide_timeout_sec;
    static constexpr time_t default_unused_dir_rm_timeout_sec = 30 * 24 * 60 * 60;      /// 30 days
    time_t unused_dir_rm_timeout_sec = default_unused_dir_rm_timeout_sec;
    static constexpr time_t default_unused_dir_cleanup_period_sec = 24 * 60 * 60;       /// 1 day
    time_t unused_dir_cleanup_period_sec = default_unused_dir_cleanup_period_sec;

    static constexpr time_t default_drop_error_cooldown_sec = 5;
    time_t drop_error_cooldown_sec = default_drop_error_cooldown_sec;

    std::unique_ptr<BackgroundSchedulePoolTaskHolder> reload_disks_task;
    std::mutex reload_disks_mutex;
    std::set<String> disks_to_reload;
    static constexpr time_t DBMS_DEFAULT_DISK_RELOAD_PERIOD_SEC = 5;
};

class TableNameHints : public IHints<>
{
public:
    TableNameHints(ConstDatabasePtr database_, ContextPtr context_)
        : context(context_),
        database(database_)
    {
    }

    /// getHintForTable tries to get a hint for the provided table_name in the provided
    /// database. If the results are empty, it goes for extended hints for the table
    /// with getExtendedHintForTable which looks for the table name in every database that's
    /// available in the database catalog. It finally returns a single hint which is the database
    /// name and table_name pair which is similar to the table_name provided. Perhaps something to
    /// consider is should we return more than one pair of hint?
    std::pair<String, String> getHintForTable(const String & table_name) const
    {
        auto results = this->getHints(table_name, getAllRegisteredNames());
        if (results.empty())
            return getExtendedHintForTable(table_name);
        return std::make_pair(database->getDatabaseName(), results[0]);
    }

    /// getExtendedHintsForTable tries to get hint for the given table_name across all
    /// the databases that are available in the database catalog.
    std::pair<String, String> getExtendedHintForTable(const String & table_name) const
    {
        /// load all available databases from the DatabaseCatalog instance
        auto & database_catalog = DatabaseCatalog::instance();
        auto all_databases = database_catalog.getDatabases();

        for (const auto & [db_name, db] : all_databases)
        {
            /// this case should be covered already by getHintForTable
            if (db_name == database->getDatabaseName())
                continue;

            TableNameHints hints(db, context);
            auto results = hints.getHints(table_name);

            /// if the results are not empty, return the first instance of the table_name
            /// and the corresponding database_name that was found.
            if (!results.empty())
                return std::make_pair(db_name, results[0]);
        }
        return {};
    }

    Names getAllRegisteredNames() const override
    {
        Names result;
        if (database)
            for (auto table_it = database->getTablesIterator(context); table_it->isValid(); table_it->next())
                result.emplace_back(table_it->name());
        return result;
    }

private:
    ContextPtr context;
    ConstDatabasePtr database;
};


/// This class is useful when creating a table or database.
/// Usually we create IStorage/IDatabase object first and then add it to IDatabase/DatabaseCatalog.
/// But such object may start using a directory in store/ since its creation.
/// To avoid race with cleanupStoreDirectoryTask() we have to mark UUID as used first.
/// Then we can either add DatabasePtr/StoragePtr to the created UUID mapping
/// or remove the lock if creation failed.
/// See also addUUIDMapping(...)
class TemporaryLockForUUIDDirectory : private boost::noncopyable
{
    UUID uuid = UUIDHelpers::Nil;
public:
    TemporaryLockForUUIDDirectory() = default;
    explicit TemporaryLockForUUIDDirectory(UUID uuid_);
    ~TemporaryLockForUUIDDirectory();

    TemporaryLockForUUIDDirectory(TemporaryLockForUUIDDirectory && rhs) noexcept;
    TemporaryLockForUUIDDirectory & operator = (TemporaryLockForUUIDDirectory && rhs) noexcept;
};

}