通过ajax同时在多个数据库中执行更新查询

I use date("h:i:s") for example. I've tried to execute the update query to multiple databases at same time, but the time could be different 1 or 2 seconds. I wonder if there were another ways to execute it at same time..

this is my script

<script type="text/javascript">
<!--
    function updateTimer() {
        var db = "1,2,",
        dbindex = db.split(","),
        countdb = 2;
        function retrieve(id) {
            if(id < countdb) {
                $.ajax({
                    url: 'update.php',
                    type: 'post',
                    data: {
                        idx : dbindex[id]-1
                    },
                    success: function (output) {
                        id++;
                        retrieve(id);
                    },
                    error: function () {
                        alert("Error Update");
                    }
                });
            }
         }
         retrieve(0);
      }
//-->
</script>

update.php

$idx = $_POST["idx"];
$conn = $db[$index[$idx]]; // testdb and test2db
$timer = date("h:i:s");
mysqli_query($conn,"update table set timer='".$timer."'");

Yes. You can send in POST an array of DB_ids;

function retrieve(id) {
     data = [];
     for(;id<countdb;id++)
     {
          data.push(dbindex[id]-1)
     }
     $.ajax({
             url: 'update.php',
             type: 'post',
             data: {
                 idx : data
             },
             success: function (output) {
                alert("Ok!");
             },
             error: function () {
                alert("Error Update");
             }
         });
     }

if(isset($_POST["idx"])){
    $idx = $_POST["idx"];
    foreach($idx as $id){
        $conn = $db[$index[$id]]; // testdb and test2db
        $timer = date("h:i:s");
        mysqli_query($conn,"update table set timer='".$timer."'");
    }
}

But You need to make some validation.