* - lowTTL : consider pre-emptive updates when the current TTL (sec)
* of the key is less than this. It becomes more likely
* over time, becoming a certainty once the key is expired.
- * - lockTSE : if the key is tombstoned or expired less (by $checkKeys)
+ * - lockTSE : if the key is tombstoned or expired (by $checkKeys) less
* than this many seconds ago, then try to have a single
* thread handle cache regeneration at any given time.
* Other threads will try to use stale values if possible.
+ * If, on miss, the time since expiration is low, the assumption
+ * is that the key is hot and that a stampede is worth avoiding.
* - tempTTL : when 'lockTSE' is set, this determines the TTL of the temp
* key used to cache values while a key is tombstoned.
* This avoids excessive regeneration of hot keys on delete() but