cluster.hpp

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#pragma once
 
/// @file userver/storages/postgres/cluster.hpp
/// @brief @copybrief storages::postgres::Cluster
 
#include <memory>
 
#include <userver/clients/dns/resolver_fwd.hpp>
#include <userver/dynamic_config/source.hpp>
#include <userver/engine/task/task_processor_fwd.hpp>
#include <userver/engine/task/task_with_result.hpp>
#include <userver/error_injection/settings_fwd.hpp>
#include <userver/testsuite/postgres_control.hpp>
#include <userver/testsuite/tasks.hpp>
 
#include <userver/storages/postgres/cluster_types.hpp>
#include <userver/storages/postgres/database.hpp>
#include <userver/storages/postgres/detail/non_transaction.hpp>
#include <userver/storages/postgres/notify.hpp>
#include <userver/storages/postgres/options.hpp>
#include <userver/storages/postgres/query.hpp>
#include <userver/storages/postgres/query_queue.hpp>
#include <userver/storages/postgres/statistics.hpp>
#include <userver/storages/postgres/transaction.hpp>
 
/// @page pg_topology uPg: Cluster topology discovery
///
/// @par Principles of PgaaS role determination
/// - Every host except master is in recovery state from PostgreSQL's POV.
/// This means the check 'select pg_is_in_recovery()' returns `false` for the
/// master and `true` for every other host type.
/// - Some hosts are in sync slave mode. This may be determined by executing
/// 'show synchronous_standby_names' on the master.
/// See
/// https://www.postgresql.org/docs/current/runtime-config-replication.html#GUC-SYNCHRONOUS-STANDBY-NAMES
/// for more information.
///
/// @par PgaaS sync slaves lag
/// By default, PgaaS synchronous slaves are working with 'synchronous_commit'
/// set to 'remote_apply'. Therefore, sync slave may be lagging behind the
/// master and thus is not truly 'synchronous' from the reader's POV,
/// but things may change with time.
///
/// @par Implementation
/// Topology update runs every second.
///
/// Every host is assigned a connection with special ID (4100200300).
/// Using this connection we check for host availability, writability
/// (master detection) and perform RTT measurements.
///
/// After the initial check we know about master presence and RTT for each host.
/// Master host is queried about synchronous replication status. We use this
/// info to identify synchronous slaves and to detect "quorum commit" presence.
///
///
/// ----------
///
/// @htmlonly <div class="bottom-nav"> @endhtmlonly
/// ⇦ @ref pg_errors | @ref scripts/docs/en/userver/pg_connlimit_mode_auto.md ⇨
/// @htmlonly </div> @endhtmlonly
 
USERVER_NAMESPACE_BEGIN
 
namespace components {
class Postgres;
}  // namespace components
 
namespace storages::postgres {
 
namespace detail {
 
class ClusterImpl;
using ClusterImplPtr = std::unique_ptr<ClusterImpl>;
 
}  // namespace detail
 
/// @ingroup userver_clients
///
/// @brief Interface for executing queries on a cluster of PostgreSQL servers
///
/// See @ref pg_user_row_types "Typed PostgreSQL results" for usage examples of
/// the storages::postgres::ResultSet.
///
/// Usually retrieved from components::Postgres component.
///
/// @todo Add information about topology discovery
class Cluster {
public:
    /// Cluster constructor
    /// @param dsns List of DSNs to connect to
    /// @param resolver asynchronous DNS resolver
    /// @param bg_task_processor task processor for blocking connection operations
    /// @param cluster_settings struct with settings fields:
    /// task_data_keys_settings - settings for per-handler command controls
    /// topology_settings - settings for host discovery
    /// pool_settings - settings for connection pools
    /// conn_settings - settings for individual connections
    /// @param default_cmd_ctls default command execution options
    /// @param testsuite_pg_ctl command execution options customizer for testsuite
    /// @param ei_settings error injection settings
    /// @note When `max_connection_pool_size` is reached, and no idle connections
    /// available, `PoolError` is thrown for every new connection
    /// request
    Cluster(
        DsnList dsns,
        clients::dns::Resolver* resolver,
        engine::TaskProcessor& bg_task_processor,
        const ClusterSettings& cluster_settings,
        DefaultCommandControls&& default_cmd_ctls,
        const testsuite::PostgresControl& testsuite_pg_ctl,
        const error_injection::Settings& ei_settings,
        testsuite::TestsuiteTasks& testsuite_tasks,
        dynamic_config::Source config_source,
        int shard_number
    );
    ~Cluster();
 
    /// Get cluster statistics
    ///
    /// The statistics object is too big to fit on stack
    ClusterStatisticsPtr GetStatistics() const;
 
    /// @name Transaction start
    /// @{
 
    /// Start a transaction in any available connection depending on transaction
    /// options.
    ///
    /// If the transaction is RW, will start transaction in a connection
    /// to master. If the transaction is RO, will start trying connections
    /// starting with slaves.
    /// @throws ClusterUnavailable if no hosts are available
    Transaction Begin(const TransactionOptions&, OptionalCommandControl = {});
 
    /// Start a transaction in a connection with specified host selection rules.
    ///
    /// If the requested host role is not available, may fall back to another
    /// host role, see ClusterHostType.
    /// If the transaction is RW, only master connection can be used.
    /// @throws ClusterUnavailable if no hosts are available
    Transaction Begin(ClusterHostTypeFlags, const TransactionOptions&, OptionalCommandControl = {});
 
    /// Start a named transaction in any available connection depending on
    /// transaction options.
    ///
    /// If the transaction is RW, will start transaction in a connection
    /// to master. If the transaction is RO, will start trying connections
    /// starting with slaves.
    /// `name` is used to set command control in config at runtime.
    /// @throws ClusterUnavailable if no hosts are available
    Transaction Begin(std::string name, const TransactionOptions&);
 
    /// Start a named transaction in a connection with specified host selection
    /// rules.
    ///
    /// If the requested host role is not available, may fall back to another
    /// host role, see ClusterHostType.
    /// If the transaction is RW, only master connection can be used.
    /// `name` is used to set command control in config at runtime.
    /// @throws ClusterUnavailable if no hosts are available
    Transaction Begin(std::string name, ClusterHostTypeFlags, const TransactionOptions&);
    /// @}
 
    /// Start a query queue with specified host selection rules and timeout for
    /// acquiring a connection.
    [[nodiscard]] QueryQueue CreateQueryQueue(ClusterHostTypeFlags flags);
 
    /// Start a query queue with specified host selection rules and timeout for
    /// acquiring a connection.
    [[nodiscard]] QueryQueue CreateQueryQueue(ClusterHostTypeFlags flags, TimeoutDuration acquire_timeout);
 
    /// @name Single-statement query in an auto-commit transaction
    /// @{
 
    /// @brief Execute a statement at host of specified type.
    /// @note You must specify at least one role from ClusterHostType here
    ///
    /// @snippet storages/postgres/tests/landing_test.cpp Exec sample
    ///
    /// @warning Do NOT create a query string manually by embedding arguments!
    /// It leads to vulnerabilities and bad performance. Either pass arguments
    /// separately, or use storages::postgres::ParameterScope.
    template <typename... Args>
    ResultSet Execute(ClusterHostTypeFlags, const Query& query, const Args&... args);
 
    /// @brief Execute a statement with specified host selection rules and command
    /// control settings.
    /// @note You must specify at least one role from ClusterHostType here
    ///
    /// @warning Do NOT create a query string manually by embedding arguments!
    /// It leads to vulnerabilities and bad performance. Either pass arguments
    /// separately, or use storages::postgres::ParameterScope.
    template <typename... Args>
    ResultSet Execute(ClusterHostTypeFlags, OptionalCommandControl, const Query& query, const Args&... args);
 
    /// @brief Execute a statement with stored arguments and specified host
    /// selection rules.
    ///
    /// @warning Do NOT create a query string manually by embedding arguments!
    /// It leads to vulnerabilities and bad performance. Either pass arguments
    /// separately, or use storages::postgres::ParameterScope.
    ResultSet Execute(ClusterHostTypeFlags flags, const Query& query, const ParameterStore& store);
 
    /// @brief Execute a statement with stored arguments, specified host selection
    /// rules and command control settings.
    ///
    /// @warning Do NOT create a query string manually by embedding arguments!
    /// It leads to vulnerabilities and bad performance. Either pass arguments
    /// separately, or use storages::postgres::ParameterScope.
    ResultSet Execute(
        ClusterHostTypeFlags flags,
        OptionalCommandControl statement_cmd_ctl,
        const Query& query,
        const ParameterStore& store
    );
    /// @}
 
    /// @brief Listen for notifications on channel
    /// @warning Each NotifyScope owns a single connection taken from the pool,
    /// which effectively decreases the number of usable connections
    NotifyScope Listen(std::string_view channel, OptionalCommandControl = {});
 
    /// Replaces globally updated command control with a static user-provided one
    void SetDefaultCommandControl(CommandControl);
 
    /// Returns current default command control
    CommandControl GetDefaultCommandControl() const;
 
    void SetHandlersCommandControl(CommandControlByHandlerMap handlers_command_control);
 
    void SetQueriesCommandControl(CommandControlByQueryMap queries_command_control);
 
    /// @cond
    /// Updates default command control from global config (if not set by user)
    void ApplyGlobalCommandControlUpdate(CommandControl);
    /// @endcond
 
    /// Replaces cluster connection settings.
    ///
    /// Connections with an old settings will be dropped and reestablished.
    void SetConnectionSettings(const ConnectionSettings& settings);
 
    void SetPoolSettings(const PoolSettings& settings);
 
    void SetTopologySettings(const TopologySettings& settings);
 
    void SetStatementMetricsSettings(const StatementMetricsSettings& settings);
 
private:
    detail::NonTransaction Start(ClusterHostTypeFlags, OptionalCommandControl);
 
    OptionalCommandControl GetQueryCmdCtl(const std::string& query_name) const;
    OptionalCommandControl GetHandlersCmdCtl(OptionalCommandControl cmd_ctl) const;
 
    detail::ClusterImplPtr pimpl_;
};
 
template <typename... Args>
ResultSet Cluster::Execute(ClusterHostTypeFlags flags, const Query& query, const Args&... args) {
    return Execute(flags, OptionalCommandControl{}, query, args...);
}
 
template <typename... Args>
ResultSet Cluster::Execute(
    ClusterHostTypeFlags flags,
    OptionalCommandControl statement_cmd_ctl,
    const Query& query,
    const Args&... args
) {
    if (!statement_cmd_ctl && query.GetName()) {
        statement_cmd_ctl = GetQueryCmdCtl(query.GetName()->GetUnderlying());
    }
    statement_cmd_ctl = GetHandlersCmdCtl(statement_cmd_ctl);
    auto ntrx = Start(flags, statement_cmd_ctl);
    return ntrx.Execute(statement_cmd_ctl, query, args...);
}
 
}  // namespace storages::postgres
 
USERVER_NAMESPACE_END