function removeFollower($followerId, $followingId)
{
//f1->f2 (f1 is no longer following f2)
if ($followerId == $followingId) {
return;
}
$redis = Redis::getInstance()->connection();
$key1 = Nest::following("user", $followerId);
$key2 = Nest::followers("user", $followingId);
$key3 = Nest::score("user", "followers");
$key4 = Nest::score("user", "followings");
// remove $followerId from $followingId's followers set
// remove $followingId from $followerId's following set
$redis->pipeline()->srem($key1, $followingId)->srem($key2, $followerId)->zincrby($key3, -1, $followingId)->zincrby($key4, -1, $followerId)->uncork();
}
