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 >> >>
