fix(database): correct metrics and improve error handling

- Fix metrics double-counting: track deltas for WaitCount/WaitDuration
  instead of adding cumulative values each tick
- Replace fmt.Printf with structured logging in pool monitor
- Add PoolOptions validation (MaxConns > 0, MinConns >= 0)
- Warn when DATABASE_URI overrides non-default PoolOptions
- Improve findAndParseConfig to report all tried files and errors
- Remove dead code in pgdb/config.go (unreachable host default)
- Fix errcheck lint issues for file.Close() calls
- Add context parameter to OpenDBMonitor() (breaking change)

database/connector.go

@@ -50,7 +50,7 @@ func createConnector(configFile string) CreateConnectorFunc {
 		if err != nil {
 			return nil, err
 		}
-		defer dbFile.Close()
+		defer func() { _ = dbFile.Close() }()
 
 		dec := yaml.NewDecoder(dbFile)
 		cfg := Config{}

database/integration_test.go

@@ -7,9 +7,7 @@ import (
 )
 
 // Mock types for testing SQLC integration patterns
-type mockQueries struct {
-	db DBTX
-}
+type mockQueries struct{}
 
 type mockQueriesTx struct {
 	*mockQueries
@@ -58,7 +56,7 @@ func TestSQLCIntegration(t *testing.T) {
 
 		// Verify our DB interface is compatible with what SQLC expects
 		var dbInterface DB[*mockQueriesTx]
-		var mockDB *mockQueries = &mockQueries{}
+		mockDB := &mockQueries{}
 		dbInterface = mockDB
 
 		// Test that our transaction helper can work with this pattern

database/metrics.go

@@ -3,10 +3,10 @@ package database
 import (
 	"context"
 	"database/sql"
-	"fmt"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"go.ntppool.org/common/logger"
 )
 
 // DatabaseMetrics holds the Prometheus metrics for database connection pool monitoring
@@ -16,6 +16,10 @@ type DatabaseMetrics struct {
 	ConnectionsInUse        prometheus.Gauge
 	ConnectionsWaitCount    prometheus.Counter
 	ConnectionsWaitDuration prometheus.Histogram
+
+	// Track last values for delta calculation (cumulative stats from sql.DBStats)
+	lastWaitCount    int64
+	lastWaitDuration time.Duration
 }
 
 // NewDatabaseMetrics creates a new set of database metrics and registers them
@@ -67,26 +71,44 @@ func monitorConnectionPool(ctx context.Context, db *sql.DB, registerer prometheu
 	ticker := time.NewTicker(30 * time.Second)
 	defer ticker.Stop()
 
+	log := logger.FromContext(ctx)
+
 	for {
 		select {
 		case <-ctx.Done():
+			log.InfoContext(ctx, "database connection pool monitor stopped")
 			return
 		case <-ticker.C:
 			stats := db.Stats()
 
+			// Update gauge metrics (current state)
 			metrics.ConnectionsOpen.Set(float64(stats.OpenConnections))
 			metrics.ConnectionsIdle.Set(float64(stats.Idle))
 			metrics.ConnectionsInUse.Set(float64(stats.InUse))
-			metrics.ConnectionsWaitCount.Add(float64(stats.WaitCount))
 
-			if stats.WaitDuration > 0 {
-				metrics.ConnectionsWaitDuration.Observe(stats.WaitDuration.Seconds())
+			// Update counter with delta (WaitCount is cumulative in sql.DBStats)
+			waitCountDelta := stats.WaitCount - metrics.lastWaitCount
+			if waitCountDelta > 0 {
+				metrics.ConnectionsWaitCount.Add(float64(waitCountDelta))
+				metrics.lastWaitCount = stats.WaitCount
+			}
+
+			// Update histogram with delta (WaitDuration is cumulative in sql.DBStats)
+			waitDurationDelta := stats.WaitDuration - metrics.lastWaitDuration
+			if waitDurationDelta > 0 {
+				metrics.ConnectionsWaitDuration.Observe(waitDurationDelta.Seconds())
+				metrics.lastWaitDuration = stats.WaitDuration
 			}
 
 			// Log connection pool stats for high usage or waiting
-			if stats.OpenConnections > 20 || stats.WaitCount > 0 {
-				fmt.Printf("Connection pool stats: open=%d idle=%d in_use=%d wait_count=%d wait_duration=%s\n",
-					stats.OpenConnections, stats.Idle, stats.InUse, stats.WaitCount, stats.WaitDuration)
+			if stats.OpenConnections > 20 || waitCountDelta > 0 {
+				log.WarnContext(ctx, "high database connection usage",
+					"open", stats.OpenConnections,
+					"idle", stats.Idle,
+					"in_use", stats.InUse,
+					"wait_count", stats.WaitCount,
+					"wait_duration", stats.WaitDuration,
+				)
 			}
 		}
 	}

database/pgdb/config.go

@@ -27,15 +27,10 @@ func CreatePoolConfig(cfg *database.PostgresConfig) (*pgxpool.Config, error) {
 		"require": true, "verify-ca": true, "verify-full": true,
 	}
 	if cfg.SSLMode != "" && !validSSLModes[cfg.SSLMode] {
-		return nil, fmt.Errorf("postgres: invalid sslmode: %s", cfg.SSLMode)
-	}
-
-	// Set defaults
-	host := cfg.Host
-	if host == "" {
-		host = "localhost"
+		return nil, fmt.Errorf("postgres: invalid sslmode: %s (valid: disable, allow, prefer, require, verify-ca, verify-full)", cfg.SSLMode)
 	}
 
+	// Apply defaults for optional fields (host is validated as required above)
 	port := cfg.Port
 	if port == 0 {
 		port = 5432
@@ -49,7 +44,7 @@ func CreatePoolConfig(cfg *database.PostgresConfig) (*pgxpool.Config, error) {
 	// Build connection string WITHOUT password
 	// We'll set the password separately in the config
 	connString := fmt.Sprintf("host=%s port=%d user=%s dbname=%s sslmode=%s",
-		host, port, cfg.User, cfg.Name, sslmode)
+		cfg.Host, port, cfg.User, cfg.Name, sslmode)
 
 	// Parse the connection string
 	poolConfig, err := pgxpool.ParseConfig(connString)

database/pgdb/pool.go

@@ -2,12 +2,14 @@ package pgdb
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"time"
 
 	"github.com/jackc/pgx/v5/pgxpool"
 	"go.ntppool.org/common/database"
+	"go.ntppool.org/common/logger"
 	"gopkg.in/yaml.v3"
 )
 
@@ -61,6 +63,19 @@ func DefaultPoolOptions() PoolOptions {
 // can be specified in the URI query string and PoolOptions are ignored.
 // When using config files, PoolOptions are applied.
 func OpenPool(ctx context.Context, options PoolOptions) (*pgxpool.Pool, error) {
+	log := logger.FromContext(ctx)
+
+	// Validate PoolOptions
+	if options.MaxConns <= 0 {
+		return nil, fmt.Errorf("pgdb: MaxConns must be positive, got: %d", options.MaxConns)
+	}
+	if options.MinConns < 0 {
+		return nil, fmt.Errorf("pgdb: MinConns must be non-negative, got: %d", options.MinConns)
+	}
+	if options.MinConns > options.MaxConns {
+		return nil, fmt.Errorf("pgdb: MinConns (%d) cannot exceed MaxConns (%d)", options.MinConns, options.MaxConns)
+	}
+
 	var poolConfig *pgxpool.Config
 	var err error
 
@@ -70,7 +85,15 @@ func OpenPool(ctx context.Context, options PoolOptions) (*pgxpool.Pool, error) {
 		if err != nil {
 			return nil, fmt.Errorf("failed to parse DATABASE_URI: %w", err)
 		}
-		// Pool settings from URI are used; PoolOptions ignored
+
+		// Log when PoolOptions differ from defaults (they will be ignored)
+		defaults := DefaultPoolOptions()
+		if options.MaxConns != defaults.MaxConns || options.MinConns != defaults.MinConns {
+			log.WarnContext(ctx, "DATABASE_URI is set; PoolOptions are ignored (use URI query parameters for pool settings)",
+				"ignored_max_conns", options.MaxConns,
+				"ignored_min_conns", options.MinConns,
+			)
+		}
 	} else {
 		// Fall back to config file approach
 		pgCfg, err := findAndParseConfig(options.ConfigFiles)
@@ -99,7 +122,7 @@ func OpenPool(ctx context.Context, options PoolOptions) (*pgxpool.Pool, error) {
 
 	// Test the connection
 	if err := pool.Ping(ctx); err != nil {
-		pool.Close()
+		pool.Close() // pgxpool.Pool.Close() doesn't return an error
 		return nil, fmt.Errorf("failed to ping database: %w", err)
 	}
 
@@ -116,35 +139,33 @@ func OpenPoolWithConfigFile(ctx context.Context, configFile string) (*pgxpool.Po
 
 // findAndParseConfig searches for and parses the first existing config file
 func findAndParseConfig(configFiles []string) (*database.PostgresConfig, error) {
-	var firstErr error
+	var errs []error
+	var triedFiles []string
 
 	for _, configFile := range configFiles {
 		if configFile == "" {
 			continue
 		}
+		triedFiles = append(triedFiles, configFile)
 
 		// Check if file exists
 		if _, err := os.Stat(configFile); err != nil {
-			if firstErr == nil {
-				firstErr = err
-			}
+			errs = append(errs, fmt.Errorf("%s: %w", configFile, err))
 			continue
 		}
 
 		// Try to read and parse the file
 		pgCfg, err := parseConfigFile(configFile)
 		if err != nil {
-			if firstErr == nil {
-				firstErr = err
-			}
+			errs = append(errs, fmt.Errorf("%s: %w", configFile, err))
 			continue
 		}
 
 		return pgCfg, nil
 	}
 
-	if firstErr != nil {
-		return nil, fmt.Errorf("no config file found: %w", firstErr)
+	if len(errs) > 0 {
+		return nil, fmt.Errorf("no valid config file found (tried: %v): %w", triedFiles, errors.Join(errs...))
 	}
 	return nil, fmt.Errorf("no valid config files provided")
 }
@@ -155,7 +176,7 @@ func parseConfigFile(configFile string) (*database.PostgresConfig, error) {
 	if err != nil {
 		return nil, fmt.Errorf("failed to open config file: %w", err)
 	}
-	defer file.Close()
+	defer func() { _ = file.Close() }()
 
 	dec := yaml.NewDecoder(file)
 	cfg := database.Config{}

database/pool.go

@@ -51,9 +51,9 @@ func OpenDBWithConfigFile(ctx context.Context, configFile string) (*sql.DB, erro
 
 // OpenDBMonitor opens a database connection with monitor-specific defaults
 // This is a convenience function for Monitor package compatibility
-func OpenDBMonitor() (*sql.DB, error) {
+func OpenDBMonitor(ctx context.Context) (*sql.DB, error) {
 	options := MonitorConfigOptions()
-	return OpenDB(context.Background(), options)
+	return OpenDB(ctx, options)
 }
 
 // findConfigFile searches for the first existing config file from the list