On Thu, Sep 11, 2014 at 3:58 PM, Vladimir Rodionov <[email protected]> wrote:
> Hi, all > > We have two isolation levels in (used to be in Scan) in Query now. See: > https://issues.apache.org/jira/browse/HBASE-11936 > > I moved isolation levels API from Scan upward to Query class. The reason: > this API was not available for Get operations. The rationals? Improve > performance of get and multi-gets over the same region. > > As many of you aware, RegionScannerImpl is heavily synchronized on internal > region's lock. Now some questions: > > 1. Is it safe to bypass this locking (in next() call) in READ_UNCOMMITTED > mode? We will do all necessary checks, of course, before calling nextRaw(). > 2. What was the reason of this locking in a first place for reads in > READ_COMMITTED mode? Except obvious - no-dirty-reads allowed? Can someone > tell me what else bad can happen? > There is only the obvious (that I know of) Vladimir. We've been so fixated on ensuring consistent view on a row, we've not done the work to allow other read types. I'm not sure what would happen if you were to skirt row lock. Try hacking on TestAtomicOperation to undo lock and see what happens? St.Ack
