PHP script to migrate mysql table to mongo collection

This is a naive PHP script I wrote to migrate data from mysql to mongo DB. I have tested transferring 10 million rows with no problem. Mongo and mysql DB credentials are not handled in this code. Even though code doesnot handle many mongo exceptions, it is good enough for normal use cases. Anybody is welcome to refine the code.

<?
// Usage ./mysqltomongo.php mysqldb mysqltable mongodb mongocollection
function mongo_connect($db,$collection) {
 $m = new Mongo(); //handle username,ports and passwords
 $mydb = $m->$db;
 if(!isset($collection)) return $mydb;
 else {
  $mycollection = $mydb->$collection;
  return $mycollection;
 }
}


$mysqldb=$argv[1];
$mysqltablename=$argv[2];
$mongodb=$argv[3];
$mongocollection=$argv[4];

$link = mysql_connect(...); //give proper info
if (!$link) {
    die('Could not connect: ' . mysql_error());
}

mysql_select_db($mysqldb);
$result = mysql_query("SELECT * from ".$mysqltablename);

$fields = mysql_num_fields($result);
$coltypes=array();
for ($i=0; $i < $fields; $i++) {
    $coltypes[mysql_field_name($result, $i)]=mysql_field_type($result, $i);
}

$mdb = mongo_connect($mongodb);
$mdb->dropCollection($mongocollection);
$collection= mongo_connect($mongodb,$mongocollection);

while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
 $newrow=transform($row,$coltypes);
 try {
         $collection->insert($newrow);
 }
 catch(MongoException $e) {
  print_r($e);
 }
}

function transform($row,$coltypes) {
 $val;
 $ret=array();
 foreach($row as $k=>$v) {
        $val=utf8_encode($v);
        if($coltypes[$k]=="real") $val=floatval($val);
        else if($coltypes[$k]=="int") $val=intval($val);
        $ret[$k]=$val;
 }
 return $ret;
}

mysql_close();
?>

Curious Case in MYSQL : Lock wait timeout exceeded on INSERT

Sounds strange, that how can a insert be locked or timed out . I had a innodb table with very frequent inserts, updated and deletes. After every few minutes, one of the inserts got timed out (50 sec is default value for innodb_lock_wait_timeout). My understanding was that timeouts happen when some other thread/transaction holds a exclusive record lock (select .. from update) for a long time. So how can a non-existent new row be already locked. I do not have a proper answer to this.

What solved my problem was dropping index and foreign key mapping, which were luckily irrelevant. Random guess is that innodb locks a range of index on insert. If you have an answer do let me know !