High-concurrency counters without sharding

Question

This question concerns two implementations of counters which are intended to scale without sharding (with a tradeoff that they might under-count in some situations):

Answer 1

Memcache gets flushed, you lose your counter. OUCH. Using a mysql database or a NOSQL solution will resolve that problem with a possible performance hit. (Redis, Tokyotyrant, MongoDB etc...) may not have that performance hit.

Keep in mind, you may want to do 2 actions:

1. keep a memcache counter just for the high performance reasons.
2. keep a log, and then get more accurate metrics from that.