Updating README.md adding 'Configuring the Database Connection Pool'. Updating main.go configurating the database connection pool with maxOpenConns, maxIdleConns and maxIdleTime values.

cmd/api/main.go

@@ -28,11 +28,15 @@ and the name of the current operating environment for the application (developme
 We'll read in the configuration settings from command-line flags when the application starts.
 */
 // Add a db struct field to hold the configuration settings for our database connection pool. For now, this only holds the DSN, which we will read in from a command-line flag.
+// Add maxOpenConns, maxIdleConns and maxIdleTime fields to hold the configuration settings for the connection pool
 type config struct {
 	port int
 	env  string
 	db   struct {
-		dsn string
+		dsn          string
+		maxOpenConns int
+		maxIdleConns int
+		maxIdleTime  time.Duration
 	}
 }
 
@@ -60,6 +64,11 @@ func main() {
 	// Use the value of the GREENLIGHT_DB_DSN environment variable as the default value for our db-dsn command-line flag.
 	flag.StringVar(&cfg.db.dsn, "db-dsn", os.Getenv("GREENLIGHT_DB_DSN"), "PostgreSQL DSN")
 
+	// Read the connection pool settings from command-line flags into the config struct.
+	flag.IntVar(&cfg.db.maxOpenConns, "db-max-open-conns", 25, "PostgreSQL max open connections")
+	flag.IntVar(&cfg.db.maxIdleConns, "db-max-idle-conns", 25, "PostgreSQL max idle connections")
+	flag.DurationVar(&cfg.db.maxIdleTime, "db-max-idle-time", 15*time.Minute, "PostgreSQL max connection idle time")
+
 	flag.Parse()
 
 	// Initialize a new structured logger which writes log entries to standard out stream.
@@ -117,6 +126,15 @@ func openDB(cfg config) (*sql.DB, error) {
 		return nil, err
 	}
 
+	// Set the maximum number of open (in-use + idle) connections in the pool. Note that passing a value less than or equal to 0 will mean there is no limit.
+	db.SetMaxOpenConns(cfg.db.maxOpenConns)
+
+	// Set the maximum number of idle connections in the pool. Again, passing a value less than or equal to 0 will mean there is no limit.
+	db.SetMaxIdleConns(cfg.db.maxIdleConns)
+
+	// Set the maximum idle timeout for connections in the pool. Passing a duration less than or equal to 0 will mean that connections are not closed due to their idle time.
+	db.SetConnMaxIdleTime(cfg.db.maxIdleTime)
+
 	// Create a context with a 5-second timeout deadline.
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()