Could the database requirements of this web app be offloaded to saas database solution

Question

For a contact management system web app that allows tennants to upload lists of contact records (having varying field structures) and then displays these back to multiple users (within tennant) one at a time is there a good p/saas database solution to handle this
-it would need to allow uploading lists with custom fields (20K records per list)
-allow updating of fields changed when users edit them (user may update 60 records a minute)
-would need to allow running queries against the lists to determine next record to display (this part utilizes set fields)
Obviously a scalable, easy to use, hassle free as possible design is the aim here.
Will it be easier than developing a local database design?
(Prefer not to use a full paas would like to keep the application tier seperate.)

Answer 1

If your queries are always against the set fields and not the custom fields, then any database would do assuming you keep the "custom" fields in blob format (xml, for example).

If that is the case then your local database design is pretty simple. If you host on amazon ec2, then you can use either of their saas database solutions (mysql or SimpleDB even).

-Dave