Hi John: Thanks for your nice answers very much. I have a further question and hope you can give me some suggestions. Following your advice, I am trying to use sumBits or addBits to sum multiple bit vectors (since they are static functions, I just separated them from the index class). However it looks like does not work. Your comments said we need to "activate" the appropriate "set" or explicitly give the activation. I did not quite understand here. I tried to read your code, this activation looks like to read data from a resource management? Actually, my target is very simple, I have multiple in-memory bit vectors already stored in bts, then I only want to perform the sum on these in-memory bit vectors. I really appreciate if you can give me some suggestions. Thanks in advance.
Regards, Mian > Hi, Mian, > > The two timing values are printed from two timing functions. They are > about the same time period. The CPU seconds is measured function > clock (or a similar function depending on system). This measurement > is based on a sampling performed by CPU, therefore reflects how long > the program is in the CPU, hence the name. The elapsed time is simply > from the wall-clock time from the begin to the end of the time period. > It is measured by gettimeofday (or a similar function if not > available). The elapsed time can also be viewed as the real time (or > total time). The difference between elapsed time and the CPU time > can be regarded as the I/O time, however, this is not exactly accurate > since the I/O operations also require CPU time. > > Typically gettimeofday returns a value that is of higher precision > than that returned by the function clock. In some cases, this can > cause the elapsed time to appear smaller than the CPU time. This is > simply a precision problem. Another way that CPU time can appear > larger than the elapsed time is when running the program with multiple > threads. > > For relatively small test datasets, most of the OSes can cache the > content of the files being used and therefore significantly diminish > the differences between the CPU time and the elapsed time. In many of > our timing measurements, we explicitly unmount the file system before > each query to make sure nothing is cached. The time we report in our > publications are usually the elapsed time, unless we are specifically > comparing CPU time. > > Hope this helps. > > John > > > On 10/22/2009 9:36 PM, Mian Lu wrote: >> Hi John: >> >> I want to confirm a question about the time measurements in the Fastbit. >> I >> notice that after a query done, there are outputs: took X CPU seconds, Y >> elapsed seconds. Then the X is the in-memory processing time, right? >> Therefore the I/O access time actually is (Y-X) seconds, am I right? >> Thanks in advance. >> >> Regards, >> Mian >> > _______________________________________________ FastBit-users mailing list [email protected] https://hpcrdm.lbl.gov/cgi-bin/mailman/listinfo/fastbit-users
