function fanoutOnPost($redis, $itemId, $feed)
{
//fan-out to followers
$key = Nest::subscribers("post", $itemId);
$followers = $redis->smembers($key);
foreach ($followers as $followerId) {
//push to subscriber's feeds
$key = Nest::feeds("user", $followerId);
$redis->lpush($key, $feed);
}
}
