ClickHouse/dbms/src/Storages/StorageKafka.h

#pragma once
#include <Common/config.h>
#if USE_RDKAFKA

#include <mutex>

#include <ext/shared_ptr_helper.h>
#include <Core/NamesAndTypes.h>
#include <Storages/IStorage.h>
#include <DataStreams/IBlockOutputStream.h>
#include <Poco/Event.h>
#include <Poco/Semaphore.h>

struct rd_kafka_s;
struct rd_kafka_conf_s;

namespace DB
{

class StorageKafka;

/** Implements a Kafka queue table engine that can be used as a persistent queue / buffer,
  * or as a basic building block for creating pipelines with a continuous insertion / ETL.
  */
class StorageKafka : public ext::shared_ptr_helper<StorageKafka>, public IStorage
{
friend class KafkaBlockInputStream;
friend class KafkaBlockOutputStream;

public:
    std::string getName() const override { return "Kafka"; }
    std::string getTableName() const override { return table_name; }
    std::string getDatabaseName() const { return database_name; }

    void startup() override;
    void shutdown() override;

    BlockInputStreams read(
        const Names & column_names,
        const SelectQueryInfo & query_info,
        const Context & context,
        QueryProcessingStage::Enum & processed_stage,
        size_t max_block_size,
        unsigned num_streams) override;

    void rename(const String & /*new_path_to_db*/, const String & new_database_name, const String & new_table_name) override
    {
        table_name = new_table_name;
        database_name = new_database_name;
    }

    void updateDependencies() override;

private:
    /// Each engine typically has one consumer (able to process 1..N partitions)
    /// It is however possible to create multiple consumers per table, as long
    /// as the total number of consumers is <= number of partitions.
    struct Consumer
    {
        Consumer(struct rd_kafka_conf_s * conf);
        ~Consumer();

        void subscribe(const Names & topics);
        void unsubscribe();

        struct rd_kafka_s * stream = nullptr;
    };
    using ConsumerPtr = std::shared_ptr<Consumer>;

    // Configuration and state
    String table_name;
    String database_name;
    Context & context;
    Names topics;
    const String brokers;
    const String group;
    const String format_name;
    const String schema_name;
     /// Total number of consumers
    size_t num_consumers;
    /// Number of actually created consumers.
    /// Can differ from num_consumers in case of exception in startup() (or if startup() hasn't been called).
    /// In this case we still need to be able to shutdown() properly.
    size_t num_created_consumers = 0;
    Poco::Logger * log;

    // Consumer list
    Poco::Semaphore semaphore;
    std::mutex mutex;
    std::vector<ConsumerPtr> consumers; /// Available consumers

    // Stream thread
    Poco::Event event_update;
    std::thread stream_thread;
    std::atomic<bool> stream_cancelled{false};

    void consumerConfiguration(struct rd_kafka_conf_s * conf);
    ConsumerPtr claimConsumer();
    ConsumerPtr tryClaimConsumer(long wait_ms);
    void pushConsumer(ConsumerPtr c);

    void streamThread();
    void streamToViews();

protected:
    StorageKafka(
        const std::string & table_name_,
        const std::string & database_name_,
        Context & context_,
        const ColumnsDescription & columns_,
        const String & brokers_, const String & group_, const Names & topics_,
        const String & format_name_, const String & schema_name_, size_t num_consumers_);
};

}

#endif