https://gitlab.com/bonusly/public/mongoid-falsehoods
Querying fields in Mongo for those with null
values will often look like this:
db.users.find({ deleted_at: null })
This is inefficient, even if you've indexed users.deleted_at
because Mongo
has to look for both documents that have a null
value in the deleted_at
field and documents that do not have a deleted_at
field set at all. If you
look at the explain results, you'll see "stage": "FETCH"
instead of
"stage": "IDXSCAN"
, which is really what we want.
Mongoid does not support storing false
instead of null
for DateTime
fields.
This gem convinces it to allow doing so.
I'd encourage you to do some baseline explain queries, look at the
executionTimeMillis
before the change. Then, add the Gem, migrate existing
data, and see the difference. This is Mongo's estimation of how long it'll take to run the quey.
Here's an example:
# before
User.where(deleted_at: nil).explain['executionStats']['executionTimeMillis'] # 4197
# after
User.where(deleted_at: false).explain['executionStats']['executionTimeMillis'] #=> 3055
So by switching from null
to false
, we shaved off about a second from this query. The improvement will vary based on the number of documents. That's with around 790,000.
Hopefully Mongo will address this Jira ticket at some point and make this gem unnecessary.
Add this line to your application's Gemfile:
gem 'mongoid-falsehoods'
And then execute:
$ bundle install
Or install it yourself as:
$ gem install mongoid-falsehoods
Turn code from this:
field :deleted_at, type: DateTime
index({ deleted_at: 1 }, background: true)
def self.not_deleted
where(deleted_at: nil)
end
def active?
deleted_at.nil?
end
to
field :deleted_at, type: DateTime, default: false
index({ deleted_at: 1 }, background: true)
def self.not_deleted
where(deleted_at: false)
end
def active?
!deleted_at
end
You'll also have to migrate existing data:
User.where(deleted_at: null).update_all(deleted_at: false)
After checking out the repo, run bin/setup
to install dependencies. Then, run rake spec
to run the tests. You can also run bin/console
for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run bundle exec rake install
. To release a new version, update the version number in version.rb
, and then run bundle exec rake release
, which will create a git tag for the version, push git commits and tags, and push the .gem
file to rubygems.org.
Bug reports and pull requests are welcome on GitHub at https://github.com/bonusly/mongoid-falsehoods. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.
The gem is available as open source under the terms of the MIT License.
Everyone interacting in the Mongo::Falsehoods project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.
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