ClickHouse/programs/odbc-bridge/ODBCPooledConnectionFactory.h

#pragma once

#include <Common/logger_useful.h>
#include <nanodbc/nanodbc.h>
#include <mutex>
#include <base/BorrowedObjectPool.h>
#include <unordered_map>


namespace DB
{
namespace ErrorCodes
{
    extern const int NO_FREE_CONNECTION;
}
}

namespace nanodbc
{

using ConnectionPtr = std::unique_ptr<nanodbc::connection>;
using Pool = BorrowedObjectPool<ConnectionPtr>;
using PoolPtr = std::shared_ptr<Pool>;

static constexpr inline auto ODBC_CONNECT_TIMEOUT = 100;


class ConnectionHolder
{
public:
    ConnectionHolder(PoolPtr pool_,
                    ConnectionPtr connection_,
                    const String & connection_string_)
        : pool(pool_)
        , connection(std::move(connection_))
        , connection_string(connection_string_)
    {
    }

    explicit ConnectionHolder(const String & connection_string_)
        : pool(nullptr)
        , connection()
        , connection_string(connection_string_)
    {
        updateConnection();
    }

    ConnectionHolder(const ConnectionHolder & other) = delete;

    ~ConnectionHolder()
    {
        if (pool != nullptr)
            pool->returnObject(std::move(connection));
    }

    nanodbc::connection & get() const
    {
        assert(connection != nullptr);
        return *connection;
    }

    void updateConnection()
    {
        connection = std::make_unique<nanodbc::connection>(connection_string, ODBC_CONNECT_TIMEOUT);
    }

private:
    PoolPtr pool;
    ConnectionPtr connection;
    String connection_string;
};

using ConnectionHolderPtr = std::shared_ptr<ConnectionHolder>;

}


namespace DB
{

static constexpr inline auto ODBC_CONNECT_TIMEOUT = 100;
static constexpr inline auto ODBC_POOL_WAIT_TIMEOUT = 10000;

template <typename T>
T execute(nanodbc::ConnectionHolderPtr connection_holder, std::function<T(nanodbc::connection &)> query_func)
{
    try
    {
        return query_func(connection_holder->get());
    }
    catch (const nanodbc::database_error & e)
    {
        tryLogCurrentException(__PRETTY_FUNCTION__);
        /// SQLState, connection related errors start with 08 (main: 08S01), cursor invalid state is 24000.
        /// Invalid cursor state is a retriable error.
        /// Invalid transaction state 25000. Truncate to 2 letters on purpose.
        /// https://docs.microsoft.com/ru-ru/sql/odbc/reference/appendixes/appendix-a-odbc-error-codes?view=sql-server-ver15
        if (e.state().starts_with("08") || e.state().starts_with("24") || e.state().starts_with("25"))
        {
            connection_holder->updateConnection();
            return query_func(connection_holder->get());
        }

        /// psqlodbc driver error handling is incomplete and under some scenarious
        /// it doesn't propagate correct errors to the caller.
        /// As a quick workaround we run a quick "ping" query over the connection
        /// on generic errors.
        /// If "ping" fails, recycle the connection and try the query once more.
        if (e.state().starts_with("HY00"))
        {
            try
            {
                just_execute(connection_holder->get(), "SELECT 1");
            }
            catch (...)
            {
                connection_holder->updateConnection();
                return query_func(connection_holder->get());
            }
        }

        throw;
    }
}


class ODBCPooledConnectionFactory final : private boost::noncopyable
{
public:
    static ODBCPooledConnectionFactory & instance()
    {
        static ODBCPooledConnectionFactory ret;
        return ret;
    }

    nanodbc::ConnectionHolderPtr get(const std::string & connection_string, size_t pool_size)
    {
        std::lock_guard lock(mutex);

        if (!factory.count(connection_string))
            factory.emplace(std::make_pair(connection_string, std::make_shared<nanodbc::Pool>(pool_size)));

        auto & pool = factory[connection_string];

        nanodbc::ConnectionPtr connection;
        auto connection_available = pool->tryBorrowObject(connection, []() { return nullptr; }, ODBC_POOL_WAIT_TIMEOUT);

        if (!connection_available)
            throw Exception("Unable to fetch connection within the timeout", ErrorCodes::NO_FREE_CONNECTION);

        try
        {
            if (!connection)
                connection = std::make_unique<nanodbc::connection>(connection_string, ODBC_CONNECT_TIMEOUT);
        }
        catch (...)
        {
            pool->returnObject(std::move(connection));
            throw;
        }

        return std::make_unique<nanodbc::ConnectionHolder>(factory[connection_string], std::move(connection), connection_string);
    }

private:
    /// [connection_settings_string] -> [connection_pool]
    using PoolFactory = std::unordered_map<std::string, nanodbc::PoolPtr>;
    PoolFactory factory;
    std::mutex mutex;
};

}