[jira] [Created] (ORC-611) Incorrect min-max stats for sub-millisecond timestamps

["Csaba Ringhofer (Jira)" <ji...@apache.org>]

Csaba Ringhofer created ORC-611:
-----------------------------------

             Summary: Incorrect min-max stats for sub-millisecond timestamps
                 Key: ORC-611
                 URL: https://issues.apache.org/jira/browse/ORC-611
             Project: ORC
          Issue Type: Bug
          Components: C++, Java
            Reporter: Csaba Ringhofer


The issue is related to the precision of storing timestamps:
- nanoseconds for the data itself
- only milliseconds for min-max statistics

Both min and max are rounded to the same value, while min should be rounded down and max should be rounded up to ensure that the values are actually within that range.

Repro in Hive:
{code}
create table tsstat (ts timestamp) stored as orc;
insert into tsstat values ("1970-01-01 00:00:00.0005")
select * from tsstat where ts = "1970-01-01 00:00:00.0005";
-- returned 0 rows
{code}

Both the Java and the C++ writer has this issue (thanks [~stigahuang] for looking them up):
https://github.com/apache/orc/blob/fea154436c37c81a16b13d879b510096cfaa2946/java/core/src/java/org/apache/orc/impl/writer/TimestampTreeWriter.java#L108
https://github.com/apache/orc/blob/fea154436c37c81a16b13d879b510096cfaa2946/c%2B%2B/src/ColumnWriter.cc#L1800

I guess that there are already files with this issue in production, so I think that the only way to fix this is to hack the reader:
- decrease/increase min/max stats with 1 ms after reading them from file
- also be careful about the values pushed down, as the same precision loss can occur there to, eg. "WHERE ts <'1970-01-01 00:00:00.0005' AND ts > '1970-01-01 00:00:00.0004'" shouldn't be converted to ts < "1970-01-01" AND ts > "1970-01-01"

The issue was discovered during an Impala review: https://gerrit.cloudera.org/#/c/15403/1/be/src/exec/hdfs-orc-scanner.cc@875



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