You could also look at Hector's approach in: https://github.com/rantav/hector/blob/master/core/src/main/java/me/prettyprint/cassandra/service/clock/MicrosecondsSyncClockResolution.java
It works well and I believe there was some performance testing done on it as well. Jim On Tue, Aug 30, 2011 at 3:43 PM, Jeremy Hanna <jeremy.hanna1...@gmail.com> wrote: > Sorry - misread your earlier email. I would login to IRC and ask in > #cassandra. I would think given the nature of nanotime you'll run into > harder to track down problems, but it may be fine. > > On Aug 30, 2011, at 2:06 PM, Jiang Chen wrote: > >> Do you see any problem with my approach to derive the current time in >> nano seconds though? >> >> On Tue, Aug 30, 2011 at 2:39 PM, Jeremy Hanna >> <jeremy.hanna1...@gmail.com> wrote: >>> Yes - the reason why internally Cassandra uses milliseconds * 1000 is >>> because System.nanoTime javadoc says "This method can only be used to >>> measure elapsed time and is not related to any other notion of system or >>> wall-clock time." >>> >>> http://download.oracle.com/javase/6/docs/api/java/lang/System.html#nanoTime%28%29 >>> >>> On Aug 30, 2011, at 1:31 PM, Jiang Chen wrote: >>> >>>> Indeed it's microseconds. We are talking about how to achieve the >>>> precision of microseconds. One way is System.currentTimeInMillis() * >>>> 1000. It's only precise to milliseconds. If there are more than one >>>> update in the same millisecond, the second one may be lost. That's my >>>> original problem. >>>> >>>> The other way is to derive from System.nanoTime(). This function >>>> doesn't directly return the time since epoch. I used the following: >>>> >>>> private static long nanotimeOffset = System.nanoTime() >>>> - System.currentTimeMillis() * 1000000; >>>> >>>> private static long currentTimeNanos() { >>>> return System.nanoTime() - nanotimeOffset; >>>> } >>>> >>>> The timestamp to use is then currentTimeNanos() / 1000. >>>> >>>> Anyone sees problem with this approach? >>>> >>>> On Tue, Aug 30, 2011 at 2:20 PM, Edward Capriolo <edlinuxg...@gmail.com> >>>> wrote: >>>>> >>>>> >>>>> On Tue, Aug 30, 2011 at 1:41 PM, Jeremy Hanna <jeremy.hanna1...@gmail.com> >>>>> wrote: >>>>>> >>>>>> I would not use nano time with cassandra. Internally and throughout the >>>>>> clients, milliseconds is pretty much a standard. You can get into >>>>>> trouble >>>>>> because when comparing nanoseconds with milliseconds as long numbers, >>>>>> nanoseconds will always win. That bit us a while back when we deleted >>>>>> something and it couldn't come back because we deleted it with >>>>>> nanoseconds >>>>>> as the timestamp value. >>>>>> >>>>>> See the caveats for System.nanoTime() for why milliseconds is a standard: >>>>>> >>>>>> http://download.oracle.com/javase/6/docs/api/java/lang/System.html#nanoTime%28%29 >>>>>> >>>>>> On Aug 30, 2011, at 12:31 PM, Jiang Chen wrote: >>>>>> >>>>>>> Looks like the theory is correct for the java case at least. >>>>>>> >>>>>>> The default timestamp precision of Pelops is millisecond. Hence the >>>>>>> problem as explained by Peter. Once I supplied timestamps precise to >>>>>>> microsecond (using System.nanoTime()), the problem went away. >>>>>>> >>>>>>> I previously stated that sleeping for a few milliseconds didn't help. >>>>>>> It was actually because of the precision of Java Thread.sleep(). >>>>>>> Sleeping for less than 15ms often doesn't sleep at all. >>>>>>> >>>>>>> Haven't checked the Python side to see if it's similar situation. >>>>>>> >>>>>>> Cheers. >>>>>>> >>>>>>> Jiang >>>>>>> >>>>>>> On Tue, Aug 30, 2011 at 9:57 AM, Jiang Chen <jia...@gmail.com> wrote: >>>>>>>> It's a single node. Thanks for the theory. I suspect part of it may >>>>>>>> still be right. Will dig more. >>>>>>>> >>>>>>>> On Tue, Aug 30, 2011 at 9:50 AM, Peter Schuller >>>>>>>> <peter.schul...@infidyne.com> wrote: >>>>>>>>>> The problem still happens with very high probability even when it >>>>>>>>>> pauses for 5 milliseconds at every loop. If Pycassa uses microseconds >>>>>>>>>> it can't be the cause. Also I have the same problem with a Java >>>>>>>>>> client >>>>>>>>>> using Pelops. >>>>>>>>> >>>>>>>>> You connect to localhost, but is that a single node or part of a >>>>>>>>> cluster with RF > 1? If the latter, you need to use QUORUM consistency >>>>>>>>> level to ensure that a read sees your write. >>>>>>>>> >>>>>>>>> If it's a single node and not a pycassa / client issue, I don't know >>>>>>>>> off hand. >>>>>>>>> >>>>>>>>> -- >>>>>>>>> / Peter Schuller (@scode on twitter) >>>>>>>>> >>>>>>>> >>>>>> >>>>> >>>>> Isn't the standard microseconds ? (System.currentTimeMillis()*1000L) >>>>> http://wiki.apache.org/cassandra/DataModel >>>>> The CLI uses microseconds. If your code and the CLI are doing different >>>>> things with time BadThingsWillHappen TM >>>>> >>>>> >>> >>> > >
