I plan on taking a look at this too. I think I had to solve it in the SQL Server adapter in my own way since it only stores milliseconds. If you care to look at our code, here are a few key sections in the tests.
http://github.com/rails-sqlserver/2000-2005-adapter/blob/master/test/cases/adapter_test_sqlserver.rb#L271 http://github.com/rails-sqlserver/2000-2005-adapter/blob/master/lib/active_record/connection_adapters/sqlserver_adapter.rb#L328 On Jan 15, 2010, at 9:45 AM, Jacob Lauemøller wrote: > Thanks for the response -- we use PostgreSQL which does store all six > microsecond digits. > > Jacob > > > On 15/01/2010, at 15.41, Chris Cruft wrote: > >> I gave up on that kind of resolution when I found that MySQL doesn't >> support it! I'll try to test the patch though. >> >> -Chris >> >> On Jan 14, 10:20 am, Jacob Lauemøller <[email protected]> >> wrote: >>> Hi all, >>> >>> The microsecond handling in >>> ActiveRecord::ConnectionAdapters::Column#fast_string_to_time and >>> ActiveRecord::ConnectionAdapters::Column#microseconds fail for some values. >>> >>> In slightly more than 1% of all possible 6-digit cases, writing a timestamp >>> to a database column and then reading it back in results in a different >>> value being returned to the program. >>> >>> So, for instance, saving the timestamp >>> >>> 2010-01-12 12:34:56.125014 >>> >>> and then loading it again from the database yields >>> >>> 2010-01-12 12:34:56.125013 >>> >>> The problem occurs when the value read is converted from string form to a >>> Ruby timestamp, so it is largely database independent (the exception being >>> drivers that override the methods, or databases that don't support >>> timestamps at all). >>> >>> The underlying problem is the use of to_i to convert from floats to ints >>> inside the affected methods. As you know, to_i simply truncates the result >>> and in some cases this causes rounding errors introduced by inherent >>> inaccuracies in the multiplication operations and decimal representation to >>> bubble up and affect the least significant digit. >>> >>> Here's a simple test that illustrates the problem: >>> >>> converted = >>> ActiveRecord::ConnectionAdapters::Column.send('fast_string_to_time', >>> "2010-01-12 12:34:56.125014") >>> assert_equal 125014, converted.usec >>> >>> This test case (and a similar one for #microseconds) fail on plain vanilla >>> Rails 2.3.5. >>> >>> I guess the best solution would be to change the ISO_DATETIME regex used to >>> extract the microsecond-part from timestamps to not include the decimal >>> point at all and then avoid the to_f and subsequent floating point >>> multiplication completely inside the failing methods. However, these >>> regexes are defined as constants on >>> ActiveRecord::ConnectionAdapters::Column::Format and therefore publicly >>> available, so the impact of changing these is difficult to ascertain. >>> >>> A simpler solution is to use round() instead of to_i to convert from the >>> intermediate floating point result to int. This works (I have verified that >>> the precision is sufficient for all possible 6-digit cases) but is about >>> 15% slower than the current method. A small price to pay for correctness, >>> in my opinion. >>> >>> I have attached a tiny patch (against 2.3.5) that switches the code to >>> using round() and a test case that verifies that the method works for a few >>> problematic cases that fail without the patch. >>> >>> I have also created a Lighthouse ticket #3693: >>> >>> https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/3... >>> >>> Could some of you please take a look and see if the patch is acceptable and >>> maybe carry it into the code base? >>> >>> Cheers >>> Jacob >>> >>> fix_microsecond_conversion.diff >>> 4KViewDownload >>> >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "Ruby on Rails: Core" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]. >> For more options, visit this group at >> http://groups.google.com/group/rubyonrails-core?hl=en. >> >> > > -- > You received this message because you are subscribed to the Google Groups > "Ruby on Rails: Core" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/rubyonrails-core?hl=en. > >
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