ClickHouse/dbms/include/DB/Interpreters/ExternalDictionaries.h

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#pragma once
#include <DB/Core/Exception.h>
#include <DB/Core/ErrorCodes.h>
#include <Yandex/MultiVersion.h>
#include <Yandex/logger_useful.h>
#include <Poco/Event.h>
#include <time.h>
#include <mutex>
#include <thread>
#include <unordered_map>
#include <chrono>
#include <random>
#include <unistd.h>
namespace DB
{
class Context;
class IDictionary;
/** Manages user-defined dictionaries.
* Monitors configuration file and automatically reloads dictionaries in a separate thread.
* The monitoring thread wakes up every @check_period_sec seconds and checks
* modification time of dictionaries' configuration file. If said time is greater than
* @config_last_modified, the dictionaries are created from scratch using configuration file,
* possibly overriding currently existing dictionaries with the same name (previous versions of
* overridden dictionaries will live as long as there are any users retaining them).
*
* Apart from checking configuration file for modifications, each non-cached dictionary
* has a lifetime of its own and may be updated if it's source reports that it has been
* modified. The time of next update is calculated by choosing uniformly a random number
* distributed between lifetime.min_sec and lifetime.max_sec.
* If either of lifetime.min_sec and lifetime.max_sec is zero, such dictionary is never updated.
*/
class ExternalDictionaries
{
private:
static const auto check_period_sec = 5;
mutable std::mutex dictionaries_mutex;
std::unordered_map<std::string, std::shared_ptr<MultiVersion<IDictionary>>> dictionaries;
std::unordered_map<std::string, std::chrono::system_clock::time_point> update_times;
std::mt19937_64 rnd_engine{getSeed()};
Context & context;
std::thread reloading_thread;
Poco::Event destroy;
Logger * log;
Poco::Timestamp config_last_modified{0};
void handleException() const
{
try
{
throw;
}
catch (const Poco::Exception & e)
{
LOG_ERROR(log, "Cannot load exter dictionary! You must resolve this manually. " << e.displayText());
return;
}
catch (...)
{
LOG_ERROR(log, "Cannot load dictionary! You must resolve this manually.");
return;
}
}
void reloadImpl();
void reloadPeriodically()
{
while (true)
{
if (destroy.tryWait(check_period_sec * 1000))
return;
reloadImpl();
}
}
static std::uint64_t getSeed()
{
timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
return ts.tv_nsec ^ getpid();
}
public:
/// Справочники будут обновляться в отдельном потоке, каждые reload_period секунд.
ExternalDictionaries(Context & context)
: context(context), log(&Logger::get("ExternalDictionaries"))
{
reloadImpl();
reloading_thread = std::thread{&ExternalDictionaries::reloadPeriodically, this};
}
~ExternalDictionaries()
{
destroy.set();
reloading_thread.join();
}
MultiVersion<IDictionary>::Version getDictionary(const std::string & name) const
{
const std::lock_guard<std::mutex> lock{dictionaries_mutex};
const auto it = dictionaries.find(name);
if (it == std::end(dictionaries))
throw Exception{
"No such dictionary: " + name,
ErrorCodes::BAD_ARGUMENTS
};
return it->second->get();
}
};
}