On Sat, Mar 19, 2011 at 12:10 PM, Barry Hunter <barrybhun...@gmail.com>wrote:
> On 19 March 2011 00:22, Nick Johnson (Google) wrote: > > > On Fri, Mar 18, 2011 at 7:03 AM, Joshua Smith wrote: > > >> > >> "Generate the next sequential ID" is a function universally provided by > >> SQL databases. Also, SQL databases always provide an efficient > count(rows) > >> function, whereas GAE does not. So I don't think it's unreasonable to > >> expect google to back-fill this deficiency as David asks. > > > > Actually, I'm not aware of any relational databases that provide an > > efficient count() implementation other than on complete tables (which is > > rarely very useful) - counting the results in an arbitrary result set > > requires iterating over all the rows, which is what App Engine does. > > At least some can answer count queries using just index scans - ie > doesnt touch the actual data. Can get close to that with keys_only - > which persumably is just what the index contains - and counting the > rows, but it still requires transfer of all keys to the application (I > think anyway) just to be discarded. > This is exactly what the .count() method does in App Engine. It's still O(n), though. -Nick Johnson > > -- > 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. > > -- Nick Johnson, Developer Programs Engineer, App Engine -- 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.
