Is Software Transactional Memory the same as database transactions?

Question

I have read alot about Software Transactional Memory, especially in relation to Haskell but I am trying to figure how it is different from database transactions? Are there some advantages I do not understand with STM?

Answer 1

The idea of a "transaction" in software transactional memory is explicitly borrowed from databases. The difference is where the transactions are implemented and how they are used.

STM is a language-level concept: a sequence of operations does not take effect until a transaction is committed. Typically this means that the values of some global/shared variables only change when a transaction succeeds. The property is enforced by the language runtime. There is no inherent notion of persistence: the variables involved in a transaction may be purely dynamic in nature (e.g., the size of a work queue).

Database transactions are an application-level concept: a sequence of data operations do not take effect until the transaction is committed. Since this is a database, persistence is fundamental: the meaning of "taking effect" inside of a database is that the data is saved in some persistent store.

You could potentially use a database and database transactions to implement a STM-style algorithm, but you'd lose the ease and convenience (and probably in most cases the performance) of a language-level implementation.