TTL "jitter"

[joshuaadickerson]

When you do a cache warmup, people often use a single TTL for a lot of keys. When the keys are related, this can cause the callback to be stampeded with requests. The solution is to make those TTLs have a slight variation. Usually that is done with a percentage of the original TTL.

I propose adding a method which will add jitter to the TTL. Something like

/**
 * @param int $ttl
 * @param float $jitter
 * @return int
 */
function jitter($ttl, $jitter)
{
    if ($jitter >= 1 || $jitter =< 0)
    {
        throw new Exception('$jitter must be between 1 and 0');
    }

    $variation = $ttl * $jitter;
    $min = ceil($ttl - $variation);
    $max = ceil($ttl + $variation);

    return rand($min, $max);
}

[tedivm]

Check it out- https://github.com/tedivm/Stash/blob/master/src/Stash/Item.php#L326

We currently subtract a random amount of time from the TTL, capped at 15%. This is a little different than your method, because our method does not allow the TTL to be extended past it's original time time, it only allows the ttl to be lowered.

[joshuaadickerson]

I completely missed that. Different from mine, but the purpose is the same. Closing.