Chris, The desire for isolation stems from the desire to amortize some computation over a number of results. Say it takes 5 seconds to compute an intersection of a couple of sets within the iterators, and then streaming back the results takes a minute or so. If I have to redo the 5 second computation many times, as in to support the reconstruction of the iterator tree, then that computation may start to dominate my query performance. Primarily, this means I need to be able to continue a scan without having to rebuild the iterators. Isolation in the scanner has that side effect. Proper isolation would be a "nice-to-have", but I can deal with not having it.
Adam On Mon, Apr 15, 2013 at 4:13 PM, Christopher <[email protected]> wrote: > Adam- > > It seems like you're talking about two features at once: > 1) Multi-table batch scanner. > 2) Scan Isolation on batch scanners like we have on regular scanners. > Is that correct? > > I can see the utility of a multi-table batch scanner, but I haven't > seen a compelling need for implementing isolation on the > batch-scanners. Do you have a use case in mind for that? > > Also, it seems that your use case for isolation is not so much the > isolated reads, but the statefulness of the iterator stack on the > server side. Is this correct? If so, I'm even more curious about your > use case for this, since that statefulness is only guaranteed per-row. > > > -- > Christopher L Tubbs II > http://gravatar.com/ctubbsii > > > On Mon, Apr 15, 2013 at 3:10 PM, Adam Fuchs <[email protected]> wrote: > > Thanks Bill, > > > > I care about latency and throughput. First available result ordering is > > fine, though. > > > > Does Guava just chain through a collection of iterators, completing one > > then moving to the next? > > > > Adam > > > > > > > > On Mon, Apr 15, 2013 at 3:06 PM, William Slacum < > > [email protected]> wrote: > > > >> How are you expecting to get results back? Guava's Iterables could > concat a > >> bunch of a Scanners together, if you didn't care about the throughput > >> aspect of it and simply wanted results from multiple tables. > >> > >> On Mon, Apr 15, 2013 at 3:00 PM, Adam Fuchs <[email protected]> wrote: > >> > >> > Is anyone else pining for a multi-table isolated batch scanner, or is > it > >> > just me? I like the automatic parallelism and balancing of the batch > >> > scanner, but I'm looking to maintain server-side state in my iterators > >> over > >> > long-running scans. I would also like to scan over multiple tables > >> > concurrently. Has anyone tried hacking something together with a pool > of > >> > non-batch scanners? > >> > > >> > Adam > >> > > >> >
