It actually is possible to track the miss rate: track how many GETs return null for keys you know must exist versus all GETs. You can either do this using memcache's INCR, or using sharded datastore counters.
On Wed, Feb 10, 2010 at 1:24 AM, a.maza <andr.m...@gmail.com> wrote: > thanks for your detailed answer. > > however, I think I won't be able to track the miss rate, since I am > not keeping information which key/value pair's I am putting in > memcache (since this would require to keep the list of keys again in > memcache). Instead, I would like to fetch the data using the newly > introduced grabTail function. > > On 10 Feb., 00:34, "Ikai L (Google)" <ika...@google.com> wrote: > > You really aren't going to get a useful answer to this question without > > doing some testing yourself. There are several factors that can influence > > this: > > > > - How many items are you putting into Memcache? > > - How large are the items? > > - Are you forcing the old items out via LRU? > > > > Other applications with even only minor deviations in numbers from yours > > will see significantly different results simply due to different usage > > patterns. > > > > I like the way you're approaching the problem - non-critical data that is > > regularly flushed. This is the way we'd like to encourage developers to > > think about how to scale their applications: differentiating between what > is > > critical, non-critical, what can be done synchronously versus what can be > > done asynchronously. I'd toy with the cron jobs and track a miss rate as > a > > function of the length of the cron job interval. There's probably a > stable > > balance between acceptable miss rate and minimizing datastore updates you > > can achieve that may very well change with time as you change the data > being > > saved or as your application's usage patterns shift. > > > > > > > > > > > > On Sun, Feb 7, 2010 at 4:34 AM, a.maza <andr.m...@gmail.com> wrote: > > > Hello, > > > > > I am keeping non-critical data (which is updated quite often) in > > > memcache. I would like to use a cronjob to fetch the data in frequent > > > intervalls from memcache in order to persist it to the datastore. > > > > > Thus, I would be interested if anyone has any experiences with the > > > average expiration time of entities that are kept in memcache (and > > > there quite frequentally accessed) - 5min? 10min? > > > > > Thanks and regards, > > > andr > > > > > -- > > > You received this message because you are subscribed to the Google > Groups > > > "Google App Engine for Java" group. > > > To post to this group, send email to > > > google-appengine-j...@googlegroups.com. > > > To unsubscribe from this group, send email to > > > google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com> > <google-appengine-java%2bÂunsubscr...@googlegroups.com> > > > . > > > For more options, visit this group at > > >http://groups.google.com/group/google-appengine-java?hl=en. > > > > -- > > Ikai Lan > > Developer Programs Engineer, Google App Enginehttp:// > googleappengine.blogspot.com|http://twitter.com/app_engine- Zitierten Text > ausblenden - > > > > - Zitierten Text anzeigen - > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine for Java" group. > To post to this group, send email to > google-appengine-j...@googlegroups.com. > To unsubscribe from this group, send email to > google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com> > . > For more options, visit this group at > http://groups.google.com/group/google-appengine-java?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 for Java" group. To post to this group, send email to google-appengine-j...@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en.
