[jira] [Created] (CASSANDRA-12923) Decimal type has inconsistent equality semantics when used in partition key

["Branimir Lambov (JIRA)" <ji...@apache.org>]

Branimir Lambov created CASSANDRA-12923:
-------------------------------------------

             Summary: Decimal type has inconsistent equality semantics when used in partition key
                 Key: CASSANDRA-12923
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12923
             Project: Cassandra
          Issue Type: Bug
            Reporter: Branimir Lambov


Unlike {{double}} or {{float}}, for {{decimal}} used as primary key in Cassandra we have that {{3 != 3.0}} even though {{3 <= 3.0}} and {{3 >= 3.0}}:
{code}
cqlsh:keyspace1> create table testdec (key decimal primary key, value int);
cqlsh:keyspace1> insert into testdec (key, value) values (3.0, 3);
cqlsh:keyspace1> select * from testdec;

 key  | value
------+-------
  3.0 |     3

(1 rows)
cqlsh:keyspace1> select * from testdec where key = 3;

 key | value
-----+-------

(0 rows)
cqlsh:keyspace1> select * from testdec where key = 3.0;

 key | value
-----+-------
 3.0 |     3

(1 rows)
cqlsh:keyspace1> select * from testdec where key >= 3 and key <= 3 ALLOW FILTERING;

 key | value
-----+-------
 3.0 |     3

(1 rows)
{code}
The reason for this is that we use the key's bytes (as produced by {{BigDecimal}}) to form the token:
{code}
cqlsh:keyspace1> select * from testdec where token(key) = token(3);

 key | value
-----+-------

(0 rows)
cqlsh:keyspace1> select * from testdec where token(key) = token(3.0);

 key | value
-----+-------
 3.0 |     3

(1 rows)
{code}
as well as to check key matches in [{{BigTableReader.getPosition}}|https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/io/sstable/format/big/BigTableReader.java#L217].

The solution is to always store a canonical form of each key. In this case, such a value that the decimal's _unscaled value_ is not divisible by 10.

This problem may be affecting other types as well.



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