On Sat, Feb 28, 2009 at 20:20, peterk <peter.ke...@gmail.com> wrote: > > It might be because it's a Saturday morning and I'm not thinking very > clearly, but I can't really seem to find a good solution to this > problem, or specifically one that might work well on GAE. > > The scenario is this (bear with me, it might sound a bit silly, but > within the context of my application it makes sense): > > Say we have users. And we have products. And say users can rate > products, so each product has a score. > > So far, so good. But now, say users can be members of groups. N > groups. And say for each group I want to track the group's score for a > given product. > > So then when a user scores a product, asides from the overall score, n > scores need to be updated - n being the number of groups the user is a > part of. > > So, I want to be able to answer queries like - what are the highest > rated products among all users? Among moms? Among my friends? > > At first blush, the naive (?) way would be for each product to have > multiple scores, one for each group, and when a user scores a product, > to update the scores for the groups it belongs too. > > But that could be an awful lot of writes (bad). Or could batch writes > come to the rescue here? Looking at the docs it's not clear if batch > writes actually minimise the cost of multiple writes versus multiple > put() calls. Is there any way to accomodate a scenario like this with > a minimum, and constant, number of writes, so that no matter how > popular the app gets and how many groups a user is a member of, the > cost of scoring a product scales in an OK way? > > Thanks for any input, apologies again if there's an obvious answer > here.. :)
I imagine the scores don't need to be perfectly accurate, off by one or two on a busy site is acceptable isn't it? So the sharded counter approach for scores might be worth looking at. And since the scores don't need to be perfectly accurate, you don't need a transaction, you can just update all the score counters in a batch update. Realistically, a user isn't going to be in more than 20 groups is he? Even for 20 groups, that's 21 writes, which could be distributed to several servers and run in parallel with batch write, it shouldn't take too long I imagine. Just my $0.02 (which is worth 200 emails with the current app engine pricing). -- Joe -- A wise man once said: never share your wisdom with others. --~--~---------~--~----~------------~-------~--~----~ 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 google-appengine+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
