How does doing currentTimeMillis() twice in a row guarantee different timestamps? And in this case, we're talking about the MemStore vs. HLog not HFile.
There is another section of the code where there is a timestamp+1 to avoid duplicates but this is something else. > -----Original Message----- > From: Ryan Rawson [mailto:ryano...@gmail.com] > Sent: Monday, January 10, 2011 2:27 PM > To: dev@hbase.apache.org > Subject: Re: question about Hregion.incrementColumnValue > > I put more comments on this: > HBASE-3021 > > Basically we needed to avoid duplicate timestamp KVs in memstore & hfile, > elsewise we might end up 'getting' the wrong value and thus messing up the > count. > > With work on ACID by stack we can avoid using that. > > -ryan > > On Mon, Jan 10, 2011 at 11:23 AM, Stack <st...@duboce.net> wrote: > > Yeah, thats going away unless Ryan comes up w/ a reason for why we > > should keep it. > > St.Ack > > > > On Mon, Jan 10, 2011 at 12:29 AM, Ryan Rawson <ryano...@gmail.com> > wrote: > >> There was a good, but complex reason. Its going away with stacks time > >> stamp patch. I'll see if I can do a better email tomorrow. > >> On Jan 9, 2011 11:42 PM, "Dhruba Borthakur" <dhr...@gmail.com> > wrote: > >>> I am looking at Hregion.incrementColumnValue(). It has the following > >>> piece of code > >>> > >>> // build the KeyValue now: > >>> 3266 KeyValue newKv = new KeyValue(row, family, > >>> 3267 qualifier, EnvironmentEdgeManager.currentTimeMillis(), > >>> 3268 Bytes.toBytes(result)); > >>> 3269 > >>> 3270 // now log it: > >>> 3271 if (writeToWAL) { > >>> 3272 long now = EnvironmentEdgeManager.currentTimeMillis(); > >>> 3273 WALEdit walEdit = new WALEdit(); > >>> 3274 walEdit.add(newKv); > >>> 3275 this.log.append(regionInfo, > >>> regionInfo.getTableDesc().getName(), > >>> 3276 walEdit, now); > >>> 3277 } > >>> > >>> It invokes EnvironmentEdgeManager.currentTimeMillis() twice, once > >>> for creating the new KV and then another time to add it to the WAL. > >>> Is this significant or just an oversight? Can we instead invoke it > >>> once before we create the new key-value and then use it for both code > paths? > >>> > >>> Thanks, > >>> dhruba > >>> > >>> -- > >>> Connect to me at http://www.facebook.com/dhruba > >> > >
