[lateforwork]

Most RDBMSs offer serializable isolation if you need it. Often you don't need it. The downside of using serializable isolation unnecessarily is reduced concurrency and throughput due to increased coordination between transactions.

[vvern]

Still, I think it’s the right default to start with serializable. Then when you have performance issues you can think long and hard about whether relaxed isolation levels will work in a big free way. Better to start with a correct application.

[lateforwork]

Starting with serializable is not free, there is a coding cost to pay to handle all the concurrency errors.

[bddicken]

Yep. Its a wonderful capability to have for some situations, but for 90% of applications SERIALIZABLE isolation is overkill.