feat: implement comprehensive database connection pooling optimization

🎯 SESSION POOLING PERFORMANCE BREAKTHROUGH!

✅ Critical Issues Fixed:
- Eliminated multiple PrismaClient instances across schedulers
- Fixed connection pool exhaustion risk in processing modules
- Implemented singleton pattern for all database connections
- Added graceful shutdown and connection cleanup

🚀 Enhanced Pooling Features:
- Dual-mode connection pooling (standard + enhanced)
- PostgreSQL native pooling with @prisma/adapter-pg
- Advanced connection monitoring and health checks
- Configurable pool limits and timeouts via environment variables
- Real-time connection statistics and metrics

📊 Performance Optimizations:
- Single shared connection pool across all schedulers
- Configurable connection limits (DATABASE_CONNECTION_LIMIT=20)
- Idle timeout management (DATABASE_POOL_TIMEOUT=10)
- Connection cycling and health validation
- Process termination signal handling

🛠️ New Infrastructure:
- lib/database-pool.ts - Advanced pooling configuration
- app/api/admin/database-health/route.ts - Connection monitoring
- Enhanced lib/prisma.ts with dual-mode support
- Comprehensive documentation in docs/database-connection-pooling.md
- Graceful shutdown handling in lib/schedulers.ts

🎛️ Environment Configuration:
- USE_ENHANCED_POOLING=true for production optimization
- DATABASE_CONNECTION_LIMIT for pool size control
- DATABASE_POOL_TIMEOUT for idle connection management
- Automatic enhanced pooling in production environments

📈 Expected Impact:
- Eliminates connection pool exhaustion under load
- Reduces memory footprint from idle connections
- Improves scheduler performance and reliability
- Enables better resource monitoring and debugging
- Supports horizontal scaling with proper connection management

Production-ready connection pooling with monitoring and health checks!

lib/prisma.ts

@@ -1,20 +1,67 @@
-// Simple Prisma client setup
+// Enhanced Prisma client setup with connection pooling
 import { PrismaClient } from "@prisma/client";
+import { createEnhancedPrismaClient } from "./database-pool.js";
+import { env } from "./env.js";
 
 // Add prisma to the NodeJS global type
-// This approach avoids NodeJS.Global which is not available
-
-// Prevent multiple instances of Prisma Client in development
 declare const global: {
   prisma: PrismaClient | undefined;
 };
 
-// Initialize Prisma Client
-const prisma = global.prisma || new PrismaClient();
+// Connection pooling configuration
+const createPrismaClient = () => {
+  // Use enhanced pooling in production or when explicitly enabled
+  const useEnhancedPooling =
+    process.env.NODE_ENV === "production" ||
+    process.env.USE_ENHANCED_POOLING === "true";
 
-// Save in global if we're in development
+  if (useEnhancedPooling) {
+    console.log("Using enhanced database connection pooling with PG adapter");
+    return createEnhancedPrismaClient();
+  }
+
+  // Default Prisma client with basic configuration
+  return new PrismaClient({
+    log:
+      process.env.NODE_ENV === "development"
+        ? ["query", "error", "warn"]
+        : ["error"],
+    datasources: {
+      db: {
+        url: env.DATABASE_URL,
+      },
+    },
+  });
+};
+
+// Initialize Prisma Client with singleton pattern
+const prisma = global.prisma || createPrismaClient();
+
+// Save in global if we're in development to prevent multiple instances
 if (process.env.NODE_ENV !== "production") {
   global.prisma = prisma;
 }
 
+// Graceful shutdown handling
+const gracefulShutdown = async () => {
+  console.log("Gracefully disconnecting from database...");
+  await prisma.$disconnect();
+  process.exit(0);
+};
+
+// Handle process termination signals
+process.on("SIGINT", gracefulShutdown);
+process.on("SIGTERM", gracefulShutdown);
+
+// Connection health check
+export const checkDatabaseConnection = async (): Promise<boolean> => {
+  try {
+    await prisma.$queryRaw`SELECT 1`;
+    return true;
+  } catch (error) {
+    console.error("Database connection failed:", error);
+    return false;
+  }
+};
+
 export { prisma };