Add a max_idle_connections parameter.

builtin/logical/postgresql/backend.go

@@ -98,6 +98,7 @@ func (b *backend) DB(s logical.Storage) (*sql.DB, error) {
 	// Set some connection pool settings. We don't need much of this,
 	// since the request rate shouldn't be high.
 	b.db.SetMaxOpenConns(connConfig.MaxOpenConnections)
+	b.db.SetMaxIdleConns(connConfig.MaxIdleConnections)
 
 	return b.db, nil
 }

builtin/logical/postgresql/path_config_connection.go

@@ -19,13 +19,24 @@ func pathConfigConnection(b *backend) *framework.Path {
 			},
 			"value": &framework.FieldSchema{
 				Type: framework.TypeString,
-				Description: `
-				DB connection string. Use 'connection_url' instead.
-				This will be deprecated.`,
+				Description: `DB connection string. Use 'connection_url' instead.
+This will be deprecated.`,
 			},
 			"max_open_connections": &framework.FieldSchema{
-				Type:        framework.TypeInt,
-				Description: "Maximum number of open connections to the database",
+				Type: framework.TypeInt,
+				Description: `Maximum number of open connections to the database;
+a zero uses the default value of two and a
+negative value means unlimited`,
+			},
+
+			// Implementation note:
+			"max_idle_connections": &framework.FieldSchema{
+				Type: framework.TypeInt,
+				Description: `Maximum number of idle connections to the database;
+a zero uses the value of max_open_connections
+and a negative value disables idle connections.
+If larger than max_open_connections it will be
+reduced to the same size.`,
 			},
 		},
 
@@ -48,6 +59,14 @@ func (b *backend) pathConnectionWrite(
 		maxOpenConns = 2
 	}
 
+	maxIdleConns := data.Get("max_idle_connections").(int)
+	if maxIdleConns == 0 {
+		maxIdleConns = maxOpenConns
+	}
+	if maxIdleConns > maxOpenConns {
+		maxIdleConns = maxOpenConns
+	}
+
 	// Verify the string
 	db, err := sql.Open("postgres", connString)
 	if err != nil {
@@ -65,6 +84,7 @@ func (b *backend) pathConnectionWrite(
 		ConnectionString:   connString,
 		ConnectionURL:      connURL,
 		MaxOpenConnections: maxOpenConns,
+		MaxIdleConnections: maxIdleConns,
 	})
 	if err != nil {
 		return nil, err
@@ -84,6 +104,7 @@ type connectionConfig struct {
 	// Deprecate "value" in coming releases
 	ConnectionString   string `json:"value"`
 	MaxOpenConnections int    `json:"max_open_connections"`
+	MaxIdleConnections int    `json:"max_idle_connections"`
 }
 
 const pathConfigConnectionHelpSyn = `