Thank! Now it makes more sense to me! Dustin, how do you do to avoid expiration date in your application? Thanks!
On Aug 3, 9:49 am, Adam Lee <[email protected]> wrote: > The main case I find expiration useful: > > You have a database that contains very important data for a popular website. > Since this data is so important and this website is so popular, the > database obviously can't service every request, so you compute this data and > give it an expiration that's a balance between "how much can my database > handle" and "just how stale can data on the website be before users start to > notice." > > Another good case: You have a counter on your website that tracks the > number of times a user performs a certain action in a day. You set this > item's expiration for end of day and it automatically goes away when it's > time to start a new counter the next day... > > > > On Tue, Aug 3, 2010 at 3:40 AM, Dustin <[email protected]> wrote: > > > On Aug 3, 12:30 am, Peter <[email protected]> wrote: > > > Hi, I am new to memcached. I am wondering why expiration is necessary > > > for the protocol. Why do we want an item to be expired if there is > > > still space to keep it? Otherwise, we can still use some replacement > > > algorithm to replace it or garbage collection algorithm to collect it? > > > Sometimes, you don't control your source data production and can't > > perform cache transformations when things change. > > > Sometimes, you really want something to go away after a certain > > amount of time because they're no longer relevant and you're best > > suited by recomputing. > > > Sometimes, you just don't trust that every event will be processed > > correctly and having some part of your application be using incorrect > > data for 15 minutes or an hour or whatever is an acceptable worst > > case. > > > Ideally, you're right -- all cache would be invalidated exactly when > > things change and nobody should ever use an expiration date on their > > caches. I have an application that does this, for everything else, > > there's TTL. > > -- > awl
