Best way to handle concurrency issues

Question

i have a LAPP (linux, apache, postgresql and php) environment, but the question is pretty the same both on Postgres or Mysql.

I have an cms app i developed, that handle

Answer 1

You will need some type of version stamp field for each record. What it is doesn't matter as long as you can guarantee that making any change to a record will result in that version stamp being different. Best practice is to then check and make sure the loaded record's version stamp is the same as the version stamp in the DB when the user clicks save, and if it's different handle it.

How you handle it is up to you. At the very least you'd want to offer to reload from the DB so the user can verify that they still want to save. One up from that would be to attempt to merge their changes into the new DB record and then ask them to verify that the merge worked correctly.

If you want to periodically poll any DB capable of handling your system should be able to take the poll load. 10 users polling once every 5 seconds is 2 transactions per second. This is a trivial load, and should be no problem at all. To keep the average load close to the actual load, just jitter the polling time slightly (instead of doing it exactly every 5 seconds, do it every 4-6 seconds, for example).