command_control.hpp

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#pragma once
 
/// @file userver/storages/redis/command_control.hpp
/// @brief @copybrief redis::CommandControl
 
#include <atomic>
#include <chrono>
#include <cstdint>
#include <optional>
#include <string>
 
#include <userver/storages/redis/impl/types.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace testsuite {
struct RedisControl;
}  // namespace testsuite
 
namespace redis {
 
inline constexpr std::chrono::milliseconds kDefaultTimeoutSingle{500};
inline constexpr std::chrono::milliseconds kDefaultTimeoutAll{2000};
inline constexpr std::size_t kDefaultMaxRetries{4};
 
/// Opaque Id of Redis server instance / any server instance.
class ServerId {
 public:
  /// Default: any server
  ServerId() = default;
 
  bool IsAny() const { return id_ == -1; }
 
  bool operator==(const ServerId& other) const { return other.id_ == id_; }
  bool operator!=(const ServerId& other) const { return !(other == *this); }
 
  bool operator<(const ServerId& other) const { return id_ < other.id_; }
 
  static ServerId Generate() {
    ServerId sid;
    sid.id_ = next_id_++;
    return sid;
  }
 
  static ServerId Invalid() { return invalid_; }
 
  int64_t GetId() const { return id_; }
 
  void SetDescription(std::string description) const;
  void RemoveDescription() const;
  std::string GetDescription() const;
 
 private:
  static std::atomic<std::int64_t> next_id_;
  static ServerId invalid_;
 
  std::int64_t id_{-1};
};
 
struct ServerIdHasher {
  std::size_t operator()(ServerId server_id) const noexcept {
    return std::hash<std::size_t>{}(server_id.GetId());
  }
};
 
struct RetryNilFromMaster {};
 
/// Can be used as an additional parameter in some commands to force retries to
/// master if slave returned a nil reply.
inline constexpr RetryNilFromMaster kRetryNilFromMaster{};
 
/// Redis command execution options
struct CommandControl {
  enum class Strategy {
    /// Same as kEveryDc
    kDefault,
 
    /// Send ~1/N requests to an instance with ping N ms
    kEveryDc,
 
    /// Send requests to Redis instances located in local DC (by Conductor info)
    kLocalDcConductor,
 
    /// Send requests to 'best_dc_count' Redis instances with the min ping
    kNearestServerPing,
  };
 
  /// Timeout for a single attempt to execute command
  std::optional<std::chrono::milliseconds> timeout_single;
 
  /// Command execution timeout, including retries
  std::optional<std::chrono::milliseconds> timeout_all;
 
  /// The maximum number of retries while executing command
  std::optional<std::size_t> max_retries;
 
  /// Server instance selection strategy
  std::optional<Strategy> strategy;
 
  /// How many nearest DCs to use
  std::optional<std::size_t> best_dc_count;
 
  /// Force execution on master node
  std::optional<bool> force_request_to_master;
 
  /// Server latency limit
  std::optional<std::chrono::milliseconds> max_ping_latency;
 
  /// Allow execution of readonly commands on master node along with replica
  /// nodes to facilitate load distribution
  std::optional<bool> allow_reads_from_master;
 
  /// Controls if the command execution accounted in statistics
  std::optional<bool> account_in_statistics;
 
  /// If set, force execution on specific shard
  std::optional<std::size_t> force_shard_idx;
 
  /// Split execution of multi-key commands (i.e., MGET) to multiple requests
  std::optional<std::size_t> chunk_size;
 
  /// If set, the user wants a specific Redis instance to handle the command.
  /// Sentinel may not redirect the command to other instances. strategy is
  /// ignored.
  std::optional<ServerId> force_server_id;
 
  /// If set, command retries are directed to the master instance
  bool force_retries_to_master_on_nil_reply{false};
 
  /// Need to be set to if you do manual retries and want retry budget to work.
  /// If set value other than 0 then request treated as retry.
  /// 0 - original request, 1 - first retry, 2 - second and so on
  size_t retry_counter{0};
 
  CommandControl() = default;
  CommandControl(const std::optional<std::chrono::milliseconds>& timeout_single,
                 const std::optional<std::chrono::milliseconds>& timeout_all,
                 const std::optional<size_t>& max_retries);
 
  bool operator==(const CommandControl& other) const;
 
  CommandControl MergeWith(const CommandControl& b) const;
  CommandControl MergeWith(const testsuite::RedisControl&) const;
  CommandControl MergeWith(RetryNilFromMaster) const;
 
  std::string ToString() const;
};
 
/// Returns CommandControl::Strategy from string
CommandControl::Strategy StrategyFromString(std::string_view s);
 
/// Returns string representation of CommandControl::Strategy
std::string_view StrategyToString(CommandControl::Strategy s);
 
}  // namespace redis
 
USERVER_NAMESPACE_END