src/Pure/General/sql.scala

     user: String,
     password: String,
     database: String = "",
     server: SSH.Server = default_server,
     server_close: Boolean = false,
+    synchronous_commit: String = "off"
   ): Database = {
     init_jdbc
 
     if (user.isEmpty) error("Undefined database user")
     if (server.host.isEmpty) error("Undefined database server host")

     val url = "jdbc:postgresql://" + server.host + ":" + server.port + "/" + name
     val ssh = server.ssh_system.ssh_session
     val print = user + "@" + server + "/" + name + if_proper(ssh, " via ssh " + ssh.get)
 
     val connection = DriverManager.getConnection(url, user, password)
-    new Database(connection, print, server, server_close)
+    val db = new Database(connection, print, server, server_close)
+
+    try {
+      db.execute_statement("SET synchronous_commit = " + SQL.string(synchronous_commit))
+    }
+    catch { case exn: Throwable => db.close(); throw exn }
+
+    db
   }
 
   def open_server(
     options: Options,
     host: String = "",

     server: SSH.Server = SSH.no_server,
     host: String = "",
     port: Int = 0,
     ssh_host: String = "",
     ssh_port: Int = 0,
-    ssh_user: String = ""
+    ssh_user: String = "",
+    synchronous_commit: String = "off"
   ): PostgreSQL.Database = {
     val db_server =
       if (server.defined) server
       else {
         open_server(options, host = host, port = port, ssh_host = ssh_host,
           ssh_port = ssh_port, ssh_user = ssh_user)
       }
     val server_close = !server.defined
     try {
       open_database(user = user, password = password, database = database,
-        server = db_server, server_close = server_close)
+        server = db_server, server_close = server_close, synchronous_commit = synchronous_commit)
     }
     catch { case exn: Throwable if server_close => db_server.close(); throw exn }
   }
 
   class Database private[PostgreSQL](