Re: Best database for web backend on Linux?

In article <70oiem$phd$1@news.bctel.net>, "Thor" <thor@echidna.net> writes: >we're still talking at cross purposes here. >if we're using "browse-mode" as the starting point .... > >The Optimistic Locking is: > >t1. Read >t2. Re-Read with Lock >t3. Update >t4. Commit / Rollback > I'm sorry, but this is not optimistic concurrency (or "browse mode"). Optimistic concurrency is essentially lock-free. So there is no "re-read". The process is: t1. Read t2. Update The update may succeed or fail, depending upon whether the data has been changed between t1 and t2. This is determined (in Sybase) via a serial that is updated (automatically) each time a row is written. [This can be done "by hand" as well, by adding to the UPDATE's WHERE clause a statement like "rowBeingUpdated.serial = @whatTheSerialWasBefore" and then checking the row count.] >You lock once you know the user wants to modify that record, not just when >they are viewing it. > This is not correct. What you describe is how to handle "very long operations" (ie. in a data browser) with locking. Optimistic concurrency exists as an alternative to your solution. - Andrew