We wouldn't need to rev the whole TypeDefinedOrder thing right? Couldn't we just define a special order for floats? Essentially it would be a tag for writers to say "hey I know about this total order thing".
On Fri, Feb 16, 2018 at 9:14 AM, Lars Volker <l...@cloudera.com> wrote: > I think one idea behind the column order fields was that if a reader does > not recognize a value there, it needs to ignore the stats. If I remember > correctly, that was intended to allow us to add new orderings for > collations, but it also seems useful to address gaps in the spec or known > broken readers. In this case we would need to deprecate the default > "TypeDefinedOrder" and replace it with something like > "TypeDefinedOrderWithCorrectOrderingForDoubles". We could also count up, > like TypeDefinedOrderV2 and so on. > > An alternative would be to list all writers that are known to have written > incorrect stats. However that will not prevent old implementations to > misinterpret correct stats - which I think was the main reason why we added > new stats fields. > > > > On Fri, Feb 16, 2018 at 9:03 AM, Alexander Behm <alex.b...@cloudera.com> > wrote: > > > I hope the common cases is that data files do not contain these special > > float values. As the simplest solution, how about writers refrain from > > populating the stats if a special value is encountered? > > > > That fix does not preclude a more thorough solution in the future, but it > > addresses the common case quickly. > > > > For existing data files we could check the writer version ignore filters > on > > float/double. I don't know whether min/max filtering is common on > > float/double, but I suspect it's not. > > > > On Fri, Feb 16, 2018 at 8:38 AM, Tim Armstrong <tarmstr...@cloudera.com> > > wrote: > > > > > There is an extensibility mechanism with the ColumnOrder union - I > think > > > that was meant to avoid the need to add new stat fields? > > > > > > Given that the bug was in the Parquet spec, we'll need to make a spec > > > change anyway, so we could add a new ColumnOrder - > > FloatingPointTotalOrder? > > > at the same time as fixing the gap in the spec. > > > > > > It could make sense to declare that the default ordering for > > floats/doubles > > > is not NaN-aware (i.e. the reader should assume that NaN was > arbitrarily > > > ordered) and readers should either implement the required logic to > handle > > > that correctly (I had some ideas here: > > > https://issues.apache.org/jira/browse/IMPALA-6527? > > > focusedCommentId=16366106&page=com.atlassian.jira. > > > plugin.system.issuetabpanels%3Acomment-tabpanel#comment-16366106) > > > or ignore the stats. > > > > > > On Fri, Feb 16, 2018 at 8:15 AM, Jim Apple <jbap...@cloudera.com> > wrote: > > > > > > > > We could have a similar problem > > > > > with not finding +0.0 values because a -0.0 is written to the > > max_value > > > > > field by some component that considers them the same. > > > > > > > > My hope is that the filtering would behave sanely, since -0.0 == +0.0 > > > > under the real-number-inspired ordering, which is distinguished from > > > > total Ordering, and which is also what you get when you use the > > > > default C/C++ operators <, >, <=, ==, and so on. > > > > > > > > You can distinguish between -0.0 and +0.0 without using total > ordering > > > > by taking their reciprocal: 1.0/-0.0 is -inf. There are some other > > > > ways to distinguish, I suspect, but that's the simplest one I recall > > > > at the moment. > > > > > > > > > >