ClickHouse/src/Storages/MergeTree/ParallelReplicasReadingCoordinator.h

#pragma once

#include <memory>
#include <Storages/MergeTree/RequestResponse.h>


namespace DB
{

/// The main class to spread mark ranges across replicas dynamically
/// The reason why it uses pimpl - this header file is included in
/// multiple other files like Context or RemoteQueryExecutor
class ParallelReplicasReadingCoordinator
{
public:
    class ImplInterface;

    explicit ParallelReplicasReadingCoordinator(size_t replicas_count_);
    ~ParallelReplicasReadingCoordinator();

    void handleInitialAllRangesAnnouncement(InitialAllRangesAnnouncement);
    ParallelReadResponse handleRequest(ParallelReadRequest request);

    /// Called when some replica is unavailable and we skipped it.
    /// This is needed to "finalize" reading state e.g. spread all the marks using
    /// consistent hashing, because otherwise coordinator will continue working in
    /// "pending" state waiting for the unavailable replica to send the announcement.
    void markReplicaAsUnavailable(size_t replica_number);

private:
    void initialize();

    std::mutex mutex;
    size_t replicas_count{0};
    CoordinationMode mode{CoordinationMode::Default};
    std::atomic<bool> initialized{false};
    std::unique_ptr<ImplInterface> pimpl;
};

using ParallelReplicasReadingCoordinatorPtr = std::shared_ptr<ParallelReplicasReadingCoordinator>;

}