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Regards Ram On Mon, Apr 29, 2013 at 7:59 PM, Aaron Zimmerman < [email protected]> wrote: > Thanks J-D. I'm interested in learning how HBase handles MVCC - do you > know of any resources explaining? I have data streaming into hbase around > 6 million records a day, and I'm scanning the tables pretty much constantly > with mapreduce jobs that rollup and store the data elsewhere. So I want to > understand better exactly which rows are present in a given scan. > > If I create a scan that reads an entire region, I would expect a "read > committed" level to lock that region during the read (which might take a > few minutes). So what happens to the rows that are inserted during the > scan? > > AZ > > > On Apr 25, 2013, at 4:34 PM, Jean-Daniel Cryans <[email protected]> > wrote: > > > Inline. > > > > J-D > > > > > > On Thu, Apr 25, 2013 at 1:09 PM, Aaron Zimmerman < > > [email protected]> wrote: > > > >> Hi, > >> > >> If a region is being written to, and a scanner takes a lease out on the > >> region, what will happen to the writes? Is there a concept of > "Transaction > >> Isolation Levels"? > >> > > > > There's MVCC, so reads can happen while someone else is writing. What you > > should expect from HBase is "read committed". > > > > > >> > >> I don't see errors in Puts while the tables are being scanned? But it > >> seems that I'm losing writes somewhere, is it possible the writes could > >> fail silently? > >> > > > > Is it temporary while you're scanning or there's really data missing at > > the end of the day? The former might happen on some older HBase versions > > while the latter should never happen unless you lower the durability > level > > yourself and have machine failures. > > > > J-D > >
