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 >>>> >>>> >> >>
