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. -- 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.
