Your CPU time will likely be lower. Your Bloom won't be able to be more than about 28 megs in size.
You may consider "Short" misses if your data doesn't all fit. (Using partial matches based on fewer characters of the complete value Look up "Robert ZCXYNVsnup" Do I have any last names that start with ZCXY No. Great don't look in data store.) You may want to play with Instance ram vs Memcache. This will likely be a factor of the Instance life and the number of running instances. From: [email protected] [mailto:[email protected]] On Behalf Of John Tantalo Sent: Sunday, December 11, 2011 7:17 PM To: [email protected] Subject: [google-appengine] Bloom filter index I wonder whether anybody has tried to build an in-memory bloom filter in front of an index to reduce datastore read operations? In my application, I have an exact-match query on a single field, and it commonly matches no results. However, I still have to pay for datastore read operations in this case. My idea was to build a bloom filter on every value of the field in my datastore. Given a query input, if the bloom filter says the value is a member of the set, I will query the datastore for it, which may or may not match results (i.e., a false positive). The bloom filter would be wrapped in an app engine model and stored in the datastore and memcached. The write rate to the datastore for this index is rather low, so I plan to update the bloom filter transactionally and cache it on every write. The updates could also be done offline in a task queue. The goal is to reduce the cost of searches, especially in the "no matches" case. I believe this change would reduce costs on datastore read operations, but increase CPU time because each request would have to read and deserialize a potentially large bloom filter from memcached. Clearly, this tradeoff could be tuned to the needs of the app, as a larger bloom filter would produce fewer false positives and wasted datastore reads. Thoughts? -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/ViVc7VJ8iOAJ. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en. -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
