[ https://issues.apache.org/jira/browse/PARQUET-1225?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Deepak Majeti reassigned PARQUET-1225: -------------------------------------- Assignee: Deepak Majeti > NaN values may lead to incorrect filtering under certain circumstances > ---------------------------------------------------------------------- > > Key: PARQUET-1225 > URL: https://issues.apache.org/jira/browse/PARQUET-1225 > Project: Parquet > Issue Type: Task > Components: parquet-cpp > Reporter: Zoltan Ivanfi > Assignee: Deepak Majeti > Priority: Major > > _This JIRA describes a generic problem with floating point comparisons that > *most probably* affects parquet-cpp. It is known to affect Impala and by > taking a quick look at the parquet-cpp code it seems to affect parquet-cpp as > well, but it has not yet been confirmed in practice._ > For comparing float and double values for min/max stats, parquet-cpp uses the > C++ less-than operator (<) that return false for comparisons involving a NaN. > This means that while garthering statistics, if a NaN is the smallest value > encountered so far (which happens to be the case after reading the first > value if that value is NaN), no other value can ever replace it, since < will > always be false. On the other hand, if NaN is not the first value, it won't > affect the min value. So the min value depends on the order of elements. > If looking for specific values while reading back the data, the NaN value may > lead to row groups being incorrectly discarded in spite of having matching > rows. For details, please see the Imapala bug IMPALA-6527. -- This message was sent by Atlassian JIRA (v7.6.3#76005)