> NOT ACCEPTABLE: re-read before update: 
> - retrofitting the additional data structures into the code 
> to carry the old data back to the persist for comparison
> - notification of data conflict happens after save but does 
> not stop the editing process NOT ACCEPTABLE: 
> timestamp/last-saved-by/hashing-the-record ( + comparisons)
> - 100+ tables in schema, all needing the additional fields to 
> the 150+ sites
> - still doesn't prevent editing (ie: only notification after 
> the event)

The checksum approach mentioned earlier would remove the necessity to change
your data structures, although it wouldn't prevent the editing problems you
mention.

> PROPOSED: mimic row locking by code using a "row lock" table 
> to record what table + row, when ( 5min expiry typical ) and 
> (more importantly) who. In addition to the standard "get 
> data", there's a "get data for editing" that re-queries (for 
> latest data) and enters an entry for the row lock table 
> (NOTE: the tables are not "locked" as such, just controlled 
> for access)
> �- only one additional table req'd (no changes to other tables)
> �- drop-dead simple notification of lock status (when, who) 
> with additional management by admin to proritise/ break 
> deadlocks. For our users, this is similar to how the existing 
> client/server system works.

The level of complexity this will add will be significant, in my opinion. I
think it's a mistake to try to mimic client-server systems too closely - web
applications aren't client-server applications. I've worked on some very
large-scale, complex web applications, and I've never had a case where this
sort of pseudo-record-locking approach was needed.

Dave Watts, CTO, Fig Leaf Software
http://www.figleaf.com/
phone: 202-797-5496
fax: 202-797-5444

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