I'm sorry, I said "products in the same", I meant "individual ratings in the same", although I think you got it.
I definitely need to have the individual ratings in the same entity group as the sharded counts or I lost safety updating them. Example: I might commit a rating (so the user sees his rating if he looks) but fail to update the count. If he later goes and changes the rating I would be removing the old total (which never got counted) and adding the new one, which is obviously wrong. This is the comment I was making earlier: these examples of using "sharded counters" seem to be completely missing on the idea that "the thing you are counting has to be in the same entity group as the sharded count or your risk double or zero counting it". The actual example from Brett is immune because he doesn't actually have anything he's counting (just button pushes), but if it were blog posts or comments then those items need to be in the same entity group so you can update the shard's count and add the post as a single, atomic transaction. -J -------------------------------------------------- From: "yejun" <[EMAIL PROTECTED]> Sent: Tuesday, November 04, 2008 9:52 AM To: "Google App Engine" <google-appengine@googlegroups.com> Subject: [google-appengine] Re: more complicated counters/ratings (sorting?) > > You can save your individual rating anywhere, you just need it for the > record. > Put you update your total rating and total user record in a > transaction counter. For average rating you only need total rating and > total user counter, you don't need individual record. > > On Nov 4, 12:15 pm, "Jay Freeman \(saurik\)" <[EMAIL PROTECTED]> > wrote: >> Ok, but this model still involves having the products in the same entity >> group as the sharded ratings, right? That isn't what I read from "use >> shards >> to track the ratings (but without using transactions)". I can easily see >> how >> you don't need a transaction to sum the shards into the total, but you >> definitely need a transaction to add the new rating and add its weight to >> the shard. -J >> >> -------------------------------------------------- >> From: "yejun" <[EMAIL PROTECTED]> >> Sent: Tuesday, November 04, 2008 9:11 AM >> To: "Google App Engine" <google-appengine@googlegroups.com> >> Subject: [google-appengine] Re: more complicated counters/ratings >> (sorting?) >> >> >> >> > You keep total rating values and number of users rated both in two >> > shard counters which are not belong to your product entity group. Then >> > update your average rating for your product's entity group >> > periodically like once every 100 request or 1000 request depends on >> > your need. So the concurrency level is only determined by the number >> > of shards not by number of users or products. >> >> > Even though the transfer data from shard counter to your entity group >> > is non-transactional, but the updating of raw records are >> > transactional, the data will be corrected next time when you update >> > average rate. Updating will only takes the time of a dozen of >> > datastore read and 1 put. >> >> > On Nov 4, 11:40 am, "Jay Freeman \(saurik\)" <[EMAIL PROTECTED]> >> > wrote: >> >> If I don't use transactions (with the ratings in the same entity >> >> groups >> >> as >> >> the shards they are being served by) then I can't be guaranteed I >> >> don't >> >> accidentally drop or double count ratings in the case of errors. :( Is >> >> the >> >> idea that you are recommending I just say "oh well, its a drop in the >> >> bucket"? -J >> >> >> -------------------------------------------------- >> >> From: "Alexander Kojevnikov" <[EMAIL PROTECTED]> >> >> Sent: Tuesday, November 04, 2008 1:12 AM >> >> To: "Google App Engine" <google-appengine@googlegroups.com> >> >> Subject: [google-appengine] Re: more complicated counters/ratings >> >> (sorting?) >> >> >> ...> I would use shards to track the ratings (but without using >> >> > transactions) and from time to time re-calculate the average from >> >> > the >> >> > shards and keep it with the product. This would allow indexing by >> >> > the >> >> > average rating, without many sacrifices. >> >> >> ... > > > --~--~---------~--~----~------------~-------~--~----~ 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-appengine@googlegroups.com 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 -~----------~----~----~----~------~----~------~--~---
