On Mon, Apr 6, 2009 at 12:58 AM, Dex Wood <slash2...@gmail.com> wrote: > > If you want to do I/O from a transaction, just use an agent to do the > I/O. Since the agent is only sent off at commit, you don't have to > worry about retries. This doesn't answer your questions about > idempotent I/O, but I think it is a strategy that you can use.
Yes, thanks very much for this tip! I have to admit I didn't (don't) understand the agent concept. I've been avoiding the subject I guess. Going to have a look now... > > On Apr 5, 2:11 pm, Hugh Winkler <hwink...@gmail.com> wrote: >> Hi all, >> >> Fromhttp://clojure.org/refs: "I/O and other activities with >> side-effects should be avoided in transactions, since transactions >> will be retried. The io! macro can be used to prevent the use of an >> impure function in a transaction." >> >> Isn't it OK to do I/O in a transaction as long as doing the operation >> multiple times has the same effect as doing it once (i.e. it's >> idempotent)? >> >> Isn't it also OK to read data in a transaction, in many circumstances? >> Even if retrying the reads results in a different end state, that's OK >> for lots of systems. Example: couldn't I safely read a stock price >> from a ticker stream within a transaction, if the purpose was only to >> have a cached value from sometime in the last 5 minutes? >> >> (I imagine there are performance considerations. Retrying some I/O >> operations could be expensive. Right now, I'm concerned with the >> logic, not the performance, but if you know something about the >> performance implications, please jump in). >> >> Just hoping someone can straighten me out if I'm wrong... I'd like to >> remove some io! macros from my code! >> >> Thanks, >> Hugh > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
