We're moving into a middle ground between Memcache and the datastore. If you can tolerate additional latency, why not store data into the datastore? You should not design assuming memcache will preserve critical data. Don't store anything in memcache that you cannot recover if evicted, even if your application runs in a degraded mode.
We exposed a "grabTail" method for Memcache but removed it due to namespace bugs. If we release this in the future, grabTail will return the next item to be evicted by LRU, so you can write an asynchronous task to flush this to the datastore. There are no plans to create triggers for eviction. On Thu, Apr 15, 2010 at 8:15 AM, peterk <peter.ke...@gmail.com> wrote: > It would, but depending on the extent of that latency it might be a > reasonable trade off for reliability. I've an app that could > definitely tolerate some % of memcache saves being higher latency if > it guaranteed I didn't lose data. > > The option of a silent background put() to the datastore upon eviction > also wouldn't necessarily incur extra latency for your memcache save, > but would instead 'just' cost you cpu_ms for those ds puts (i'm sure > those DS puts could be asynchronous and your memcache operation could > return without waiting for them to finish). > > Again, I don't know if it's practical on the backend, feasible to > implement. But I believe other database systems offer that kind of > write-behind cache. > > On Apr 15, 3:45 pm, Wooble <geoffsp...@gmail.com> wrote: > > On Apr 15, 9:48 am, peterk <peter.ke...@gmail.com> wrote: > > > > > It'd be great if memcache could throw a warning or error upon a put to > > > memcache, if that put will cause an eviction of another value, and ask > > > you to retry your put with a token to confirm you're OK with the > > > eviction. > > > > It's a cache. That would add annoying latency. > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine" group. > To post to this group, send email to google-appeng...@googlegroups.com. > To unsubscribe from this group, send email to > google-appengine+unsubscr...@googlegroups.com<google-appengine%2bunsubscr...@googlegroups.com> > . > For more options, visit this group at > http://groups.google.com/group/google-appengine?hl=en. > > -- Ikai Lan Developer Programs Engineer, Google App Engine http://googleappengine.blogspot.com | http://twitter.com/app_engine -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
