We have solved this issue recently. It is not just a problem in Hive. Contact me offline if you need more details.
-Bharath ________________________________ From: Johnny Zhang <xiao...@cloudera.com> To: Johnny Zhang <xiao...@cloudera.com>; Mark Grover <grover.markgro...@gmail.com>; hive <dev@hive.apache.org> Sent: Monday, December 17, 2012 5:13 PM Subject: Re: Review Request: float and double calculation is inaccurate in Hive > On Dec. 18, 2012, 12:38 a.m., Mark Grover wrote: > > http://svn.apache.org/repos/asf/hive/trunk/ql/src/java/org/apache/hadoop/hive/ql/udf/UDFOPDivide.java, > > line 50 > > <https://reviews.apache.org/r/8653/diff/1/?file=240423#file240423line50> > > > > 10 seems to be a rather arbitrary number for scale. Any particular > >reason you are using it? Maybe we should invoke the method where no scale > >needs to be specified. > > Johnny Zhang wrote: > Hi, Mark, thanks for reviewing it. The reason using 10 is because it is >the same as mysql default precision setting. Just want to make the calculation >result identical to mysql's I think I did tried without specify scale, and the result is different from mysql. I agree hard coding the scale is not a good way. Open to other suggestions. - Johnny ----------------------------------------------------------- This is an automatically generated e-mail. To reply, visit: https://reviews.apache.org/r/8653/#review14625 ----------------------------------------------------------- On Dec. 18, 2012, 12:37 a.m., Johnny Zhang wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/8653/ > ----------------------------------------------------------- > > (Updated Dec. 18, 2012, 12:37 a.m.) > > > Review request for hive. > > > Description > ------- > > I found this during debug the e2e test failures. I found Hive miss calculate > the float and double value. Take float calculation as an example: > hive> select f from all100k limit 1; > 48308.98 > hive> select f/10 from all100k limit 1; > 4830.898046875 <--added 04875 in the end > hive> select f*1.01 from all100k limit 1; > 48792.0702734375 <--should be 48792.0698 > It might be essentially the same problem as > http://effbot.org/pyfaq/why-are-floating-point-calculations-so-inaccurate.htm > But since e2e test compare the results with mysql and seems mysql does it > right, so it is worthy fixing it in Hive. > > > This addresses bug HIVE-3715. > https://issues.apache.org/jira/browse/HIVE-3715 > > > Diffs > ----- > > >http://svn.apache.org/repos/asf/hive/trunk/ql/src/java/org/apache/hadoop/hive/ql/udf/UDFOPDivide.java > 1423224 > >http://svn.apache.org/repos/asf/hive/trunk/ql/src/java/org/apache/hadoop/hive/ql/udf/UDFOPMultiply.java > 1423224 > > Diff: https://reviews.apache.org/r/8653/diff/ > > > Testing > ------- > > I did test to compare the result with mysql default float precision setting, > the result is identical. > > query: select f, f*1.01, f/10 from all100k limit 1; > mysql result: 48309 48792.0702734375 4830.898046875 > hive result: 48308.98 48792.0702734375 4830.898046875 > > > I apply this patch and run the hive e2e test, and the tests all pass (without > this patch, 5 related failures) > > > Thanks, > > Johnny Zhang > >
