Jruby precision issue with reading float values in mysql db


I was trying to upgrade from 1.1.6 to 1.2.0 and noticed a strange
issue with floats. In Jruby 1.2.0, a float like 2.52342 is read as
2.52342009544373 from the DB.

A few steps to reproduce this.

  1. Migration: t.float :reading
  2. Fixture: reading: 2.52342
  3. Run script/console

jruby script/console
Loading development environment (Rails 2.2.2)

=> 2.52342009544373

Any idea if this has been logged as a bug or if there is a workaround?

The issue persists with both 1.3.0 RC1 & RC2.

It seems the problem is that we’re showing the actual machine precision
here. Floats are rarely 100% accurate, and this is likely a case where
it’s losing some accuracy going into or coming out of the database. It’s
possible there’s a bug somewhere, but expecting floats to always be an
exact amount generally leads to bugs.

At any rate, can you file an issue for this in JRuby’s bug tracker, and
if it’s valid we’ll try to fix it :slight_smile: