2010/1/5 Mark McGranaghan <mmcgr...@gmail.com>: > Hi Rick, > >> 1) Is it possible to implement a join across several collections, >> within the same database snapshot? > > Not, not yet. I may add a feature in the future that looks like: > > ["snapshot", <time-to-live>] > => <snap-label> > > ["on-snapshot" <snap-label> <query-1>] > => <query-1-result> > > ["on-snapshot" <snap-label> <query-2-based-on-query-1-result>] > => <query-2 result> > > Once again, Clojure's persistent data structures to the rescue! > > Also, would you be willing to describe a little more what type of > joins you'de like to be able to do in FleetDB?
In truth, I don't know; as I've not really thought about what I'd use fleetdb for or whether I even need such a thing... So my interest at this stage is primarily academic, it just stood out as an omission. However at the most basic level I'd expect being able to do simple inner joins on a foreign key would be nice. You explicitly state creating a snapshot, but when I was looking for information on joins I was wondering whether it might have been possible using the multi-read, perhaps where the second query would operate on the result of the first? Out of curiosity I glanced through the code to see whether you were making use of the STM, agents etc... and was surprised by their omission. Is there a reason you chose to use the executor thread pool over agents... Am I right in thinking the reason you're not using refs is because you don't currently allow joins... therefore updates require no coordination beyond atomic updates. If you add the ability to join across collections will you need them? How about changes to indexed values? Are these atomically updated in the record and index? Sorry for the dumb questions... I'm still learning clojure and I'm curious :-) R.
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