feat: add database debug logging

README.md

@@ -43,7 +43,7 @@ cd ..
 ./build/bin/cards /path/to/config.json
 ```
 
-Для подробного вывода этапов запуска и итоговой конфигурации используйте флаг `--debug`. Пароль базы данных в таком выводе не раскрывается.
+Для подробного вывода этапов запуска и итоговой конфигурации используйте флаг `--debug`. Он также включает диагностику работы с БД: создание схемы, запуск и остановку воркеров, запросы, выбранную стратегию выборки, результаты и переподключения после ошибок. Пароль базы данных в таком выводе не раскрывается.
 
 ```bash
 ./build/bin/cards --debug

src/database.cpp

@@ -1,13 +1,17 @@
 #include "database.hpp"
 #include <chrono>
+#include <iostream>
+#include <syncstream>
 
-Database::Database(const DatabaseConfig& cfg, int workers)
+Database::Database(const DatabaseConfig& cfg, int workers, bool debug)
     : connStr(
         "host=" + cfg.host +
         " port=" + std::to_string(cfg.port) +
         " dbname=" + cfg.dbname +
         " user=" + cfg.user +
-        " password=" + cfg.password) {
+        " password=" + cfg.password),
+      debug(debug) {
+    logDebug("Creating schema for random_data");
     {
         pqxx::connection probe(connStr);
         pqxx::work txn(probe);
@@ -22,6 +26,7 @@ Database::Database(const DatabaseConfig& cfg, int workers)
         );
         txn.commit();
     }
+    logDebug("Schema is ready; starting " + std::to_string(workers) + " database worker(s)");
     for (int i = 0; i < workers; ++i) {
         threadPool.emplace_back([this, i]() { worker(i); });
     }
@@ -36,16 +41,20 @@ void Database::stop() {
         std::lock_guard<std::mutex> lock(mtx);
         stopFlag = true;
     }
+    logDebug("Stopping database workers");
     cv.notify_all();
     for (auto& t : threadPool) {
         if (t.joinable()) {
             t.join();
         }
     }
+    logDebug("All database workers stopped");
 }
 
 void Database::worker(int id) {
+    logDebug("Worker " + std::to_string(id) + " connecting to database");
     auto conn = std::make_unique<pqxx::connection>(connStr);
+    logDebug("Worker " + std::to_string(id) + " connected to database");
     std::mt19937 rng(std::random_device{}());
 
     for (;;) {
@@ -53,7 +62,10 @@ void Database::worker(int id) {
         {
             std::unique_lock<std::mutex> lock(mtx);
             cv.wait(lock, [&] { return stopFlag || !queue.empty(); });
-            if (stopFlag && queue.empty()) return;
+            if (stopFlag && queue.empty()) {
+                logDebug("Worker " + std::to_string(id) + " stopped");
+                return;
+            }
             task = std::move(queue.front());
             queue.pop();
         }
@@ -61,23 +73,36 @@ void Database::worker(int id) {
         json res;
         try {
             if (task.op == Op::RandomRecord) {
+                logDebug("Worker " + std::to_string(id) + " fetching one random record");
                 res = getRandomRecord(*conn, rng);
             } else {
+                logDebug("Worker " + std::to_string(id) + " fetching " + std::to_string(task.count)
+                         + " random record(s)");
                 res = getRandomRecords(*conn, rng, task.count, task.med, task.max);
             }
-        } catch (const std::exception&) {
+        } catch (const std::exception& e) {
+            logDebug("Worker " + std::to_string(id) + " database error: " + e.what()
+                     + "; reconnecting");
             conn = std::make_unique<pqxx::connection>(connStr);
+            logDebug("Worker " + std::to_string(id) + " reconnected to database");
             res = json{{"error", "Database error"}};
         }
+        logDebug("Worker " + std::to_string(id) + " completed request"
+                 + (res.contains("error") ? ": " + res["error"].get<std::string>() : ""));
         task.cb(std::move(res));
     }
 }
 
 void Database::enqueue(Task task) {
+    std::size_t queueSize;
+    const char* operation = task.op == Op::RandomRecord ? "one random record" : "random records";
     {
         std::lock_guard<std::mutex> lock(mtx);
         queue.push(std::move(task));
+        queueSize = queue.size();
     }
+    logDebug("Queued request for " + std::string(operation)
+             + "; pending requests: " + std::to_string(queueSize));
     cv.notify_one();
 }
 
@@ -91,6 +116,7 @@ void Database::getRandomRecords(int count, int med, int max, Callback cb) {
 
 json Database::getRandomRecord(pqxx::connection& conn, std::mt19937& rng) {
     int totalCount = getTotalCount(conn);
+    logDebug("random_data contains " + std::to_string(totalCount) + " record(s)");
 
     if (totalCount == 0) {
         return json{
@@ -100,6 +126,7 @@ json Database::getRandomRecord(pqxx::connection& conn, std::mt19937& rng) {
 
     std::uniform_int_distribution<int> idDist(1, totalCount);
     int randomId = idDist(rng);
+    logDebug("Selected random record ID " + std::to_string(randomId));
 
     pqxx::work txn(conn);
 
@@ -111,6 +138,7 @@ json Database::getRandomRecord(pqxx::connection& conn, std::mt19937& rng) {
     );
 
     if (result.empty()) {
+        logDebug("Selected record no longer exists; falling back to the first available record");
         result = txn.exec("SELECT id, name, text, description, created_at FROM random_data LIMIT 1");
     }
 
@@ -137,6 +165,7 @@ json Database::getRandomRecord(pqxx::connection& conn, std::mt19937& rng) {
 }
 
 json Database::getRandomRecordsFast(pqxx::connection& conn, const int count) {
+    logDebug("Using recursive CTE strategy for " + std::to_string(count) + " record(s)");
     pqxx::work txn(conn);
 
     std::string query =
@@ -210,6 +239,7 @@ json Database::getRandomRecordsFast(pqxx::connection& conn, const int count) {
     }
 
     txn.commit();
+    logDebug("Recursive CTE returned " + std::to_string(response.size()) + " record(s)");
 
     return {
         {"data", response},
@@ -220,6 +250,8 @@ json Database::getRandomRecordsFast(pqxx::connection& conn, const int count) {
 }
 
 json Database::getRandomRecordsSlow(pqxx::connection& conn, std::mt19937& rng, const int count, const int totalCount) {
+    logDebug("Using individual-ID strategy for " + std::to_string(count) + " of "
+             + std::to_string(totalCount) + " record(s)");
     std::set<int> ids;
     {
         std::uniform_int_distribution<int> idDist(1, totalCount);
@@ -259,6 +291,7 @@ json Database::getRandomRecordsSlow(pqxx::connection& conn, std::mt19937& rng, c
     }
 
     txn.commit();
+    logDebug("Individual-ID query returned " + std::to_string(response.size()) + " record(s)");
 
     return {
         {"data", response},
@@ -277,6 +310,8 @@ json Database::getRandomRecords(pqxx::connection& conn, std::mt19937& rng, int c
     }
 
     int totalCount = getTotalCount(conn);
+    logDebug("Requested " + std::to_string(count) + " random record(s); "
+             + std::to_string(totalCount) + " available");
 
     if (totalCount == 0) {
         return json{
@@ -286,10 +321,12 @@ json Database::getRandomRecords(pqxx::connection& conn, std::mt19937& rng, int c
     }
 
     if (count > totalCount) {
+        logDebug("Reducing requested count to available record count");
         count = totalCount;
     }
 
     if (count > max) {
+        logDebug("Reducing requested count to configured maximum of " + std::to_string(max));
         count = max;
     }
 
@@ -329,3 +366,9 @@ std::string Database::getQueryRandomIds(const int count) {
     query += ") ORDER BY id";
     return query;
 }
+
+void Database::logDebug(const std::string& message) const {
+    if (debug) {
+        std::osyncstream(std::cout) << "[debug][database] " << message << '\n';
+    }
+}

src/database.hpp

@@ -19,7 +19,7 @@ class Database {
 public:
     using Callback = std::function<void(json)>;
 
-    explicit Database(const DatabaseConfig& config, int workers = 2);
+    explicit Database(const DatabaseConfig& config, int workers = 2, bool debug = false);
     ~Database();
 
     Database(const Database&) = delete;
@@ -42,6 +42,7 @@ private:
     void worker(int id);
     void enqueue(Task task);
     void stop();
+    void logDebug(const std::string& message) const;
 
     json getRandomRecord(pqxx::connection& conn, std::mt19937& rng);
     json getRandomRecords(pqxx::connection& conn, std::mt19937& rng, int count, int med, int max);
@@ -56,4 +57,5 @@ private:
     std::condition_variable cv;
     std::queue<Task> queue;
     bool stopFlag = false;
+    bool debug;
 };

src/main.cpp

@@ -59,7 +59,7 @@ int main(int argc, char* argv[]) {
         }
 
         std::cout << "Connecting to database..." << std::endl;
-        auto db = std::make_shared<Database>(config.database);
+        auto db = std::make_shared<Database>(config.database, 2, debug);
         std::cout << "Database connected successfully!" << std::endl;
 
         if (debug) {