Killian, Are all of these entities global or are some or all of them user-specific? How often do the entities relationships change, are LOs tagged / untagged often? Are LOs frequently added and deleted? Are deletes or adds more often? Same questions for Tags. Is it important that the Imp values are sequential? How many Tags would a typical LO have? How many LOs would a typical Tag have?
Your second option may not be that bad if tag deletes are not that common. You would be able to use the task queue or something to handle removing the Tag in the background. Depending on the answers to the questions above, you could also denormalize the structures so that you have a LOTag kind. Then you would be able to query that object easily, and if it is heavily denormailized you may not need a lot of additional queries. Just some thoughts, Robert On Mon, Mar 22, 2010 at 4:36 AM, Killian <killian.levac...@gmail.com> wrote: > Hi everyone, > > I'm trying to build a (seemingly) relatively simple 'Gmail like' label > functionality using the app engine and am concerned about making > proper use of app engine specific characteristics as much as possible > to avoid fan out issues and make the code scalable. > > Here is the problem: > I have a very large number of Learning Object entities LO each > possessing a knowledge value K (between 0% and 100%). Each of these LO > can be tagged with several tags T (a tag can contain a very large nbr > of LO). For the moment this is exactly like gmail labels. The only > difference is that each of these tags order their LO differently > according to their importance Imp within each tag. So for instance, > LO1 could be tagged with T1 and T2 and have importances Imp5 and > Imp155 within each tag (an importance of 0 represents the most > important learning object) > > Now the query I would like to make is the following: Give me a list of > Learning objects tagged with T1 where K<30 and order these by tag > importance Imp. > > 1/ So my first idea was simply to create a Tag entity with a > List<Key> LO feature ordering each LO. By doing this, getting the LO > in Imp order becomes easy (since LO are stored in order) but only > getting those with a value of K<30 means I need to query each of these > LO to find out if they have the appropriate K value. > > 2/ So then I thought of creating a List<String> tags feature in each > LO entity, query for LO's with tag T1 and K<30 and then use the Tag > entity to find the correct order. This seems cumbersome, and also, I'm > assuming whenever a user needs to delete a Tag, this creates a fan out > issue since each LO needs to be accessed to remove T1 from it's list > right? > > What is the correct approach to use in this case? Any recomendations? > > I found a talk by Brett Slatkin covering these issues which helped but > I'm still having problems getting my head around this problem. > http://code.google.com/events/io/2009/sessions/BuildingScalableComplexApps.html > > I would really appreciate your input ! :-) > > Thanks in advance > > -- > 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. > > -- 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.
