Slim Attributes

Slim Attributes boosts speed in Mysql/Rails ActiveRecord Models by avoiding instantiating Hashes for each result row, and lazily instantiating attributes as needed.

How fast is it?

Notice that the speed relative to using plain ActiveRecord depends on how many attributes are accessed in the model objects (because slim_attributes lazily instantiates them into strings).

Overview

This is a small patch to the ActiveRecord Mysql adaptor that stops rails from using the existing all_hashes / each_hash mechanism - which is what is called when you do a find.

It is faster, and uses less memory.

Measuring with just ActiveRecord code - fetching stuff from the database - we see anything from very little up to a 50% (or more) speed increase, but I suppose it really depends on your system and environment, and what you are doing with the results from the database. Measure your own system and send me the results!

Download

From rubyforge

Installation

You’re going to need the mysql headers for this to work.

Try:
gem install slim-attributes -- --with-mysql-config
or:
gem install slim-attributes

then add this to environment.rb:
require 'slim_attributes'

Description

The reason for overriding all_hashes is threefold:

making a hash of each and every row returned from the database is slow
ruby makes frozen copies of each column name string (for the keys) which results in a great many strings which are not really needed
we observe that it’s not often that all the fields of rows fetched from the database are actually used

So this is an alternative implementation of all_hashes that returns a ‘fake hash’ which contains a hash of the column names (the same hash of names is used for every row), and also contains the row data in an area memcpy’d directly from the mysql API. The field contents are then instantiated into Ruby strings on demand - ruby strings are only made if you need them. Note that if you always look at all the columns when you fetch data from the database then this won’t necessarily be faster that the unpatched mysql adapter. But it won’t be much slower either, and we do expect that most times not all the columns from a result set are accessed.

The returned objects (of class Mysql::Result::RowHash) quack almost exactly like hashes - if you do anything other than fetch or set an attribute then a real hash will be instantiated, and any methods called will be put to work on that. So this should be safe to use even if you access @attributes directly from your code.

No warranty - this plugin should be considered experimental at this stage. However, that said, we are using it in our production environment with good results.