garysweaver/ignore_nsec

Some versions of OS's and databases only support microsecond precision. Using this gem makes Ruby ignore nanoseconds in Time comparisons to hopefully help avoid the time != time problem.

Ignore Nsec

Have ever run into a strange problem in Ruby where two Time instances that looked the same were different? You may have run into the nanosecond precision problem.

The ignore_nsec gem takes care of that. With the gem, nanoseconds are still available via the nsec and other methods, but the <=> method on Time instances will ignore nanoseconds, which resolves problems caused by some operating systems providing nanosecond precision that is more precise than what the database accepts, so when you compare a time before persisting, then retrieve the record and compare times, the times will be different. For example, let's setup two times with different nanoseconds:

# note: We are manually setting Time nsec here, so it isn't checking that
# your OS is returning nsec in the current time, nor is it checking your
# database stores or does not store nsec with (date)time.
#
a = Time.at(421.158888888)
b = Time.at(421.15888888)
a == b # => false

While using this gem, Time instances will return to_i <=> other.to_i if the object that a Time is being compared to looks like a Time (i.e. responds to nsec). Using the same example:

a == b # => true

Checking nsec

Run Time.now a few times in irb and see if it always seems to return the last three as '0' or if it has 6 or fewer significant digits (non-zero digits to the right of the decimal point). In OS X 10.9, I see that it does not support nanosecond precision in Time (by default, at least), e.g.:

Time.now # => 220359000

In my Linux VM, it does use nsec precision, e.g.:

Time.now # => 543686757

Setup

In your Gemfile:

gem 'ignore_nsec'

Then run:

bundle install

Performance

In testing, the revised <=> method only for the Time object seemed to be about 10x slower (0.00001029 sec vs. 0.00000105 sec). This is probably not a problem for small numbers of calls, but would become a concern if you were doing anything that required a lot of date comparisons, such as sorting millions of records in Ruby by time (vs. sorting in the database via query, which hopefully you would be able to do instead).

License

Copyright (c) 2014 FineLine Prototyping, Inc., released under the MIT license.