# Performance question

**URL:** <https://www.ruby-forum.com/t/performance-question/172045>\
**Category:** Ruby\
**Created:** [July 13, 2009, 9:15pm UTC](https://www.ruby-forum.com/t/performance-question/172045 "2009-07-13T21:15:15Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![pitosalas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a4c791/32.png) [@pitosalas](https://www.ruby-forum.com/u/pitosalas)\
**Post date:** [July 13, 2009, 9:15pm UTC](https://www.ruby-forum.com/t/performance-question/172045/1 "2009-07-13T21:15:15Z")

</div>

I have a scenario where I will be storing thousands of objects in an  
array. Each one will have, say, two attributes, name and age. Some of  
them may have other attributes in addition.

Note: I don’t need to have any methods, inheritance or any other  
‘class-ish’ behavior. Just the data.

Here are three representations. Which one will be faster? Which one will  
be smaller?

class O  
def initialize (n, a)  
@name = n  
@age = a  
end

O.new(“jack”, 11)

OR

{:name =\> “Jack”, :age =\> 11}

OR

Struct.new(“O”, :name, :age)  
O.new(“Jack”, 11)

---

<div class="post-metadata">

**Author:** ![pitosalas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a4c791/32.png) [@pitosalas](https://www.ruby-forum.com/u/pitosalas)\
**Post date:** [July 13, 2009, 9:27pm UTC](https://www.ruby-forum.com/t/performance-question/172045/2 "2009-07-13T21:27:32Z")

</div>

Pito S. wrote:

> I have a scenario where I will be storing thousands of objects in an  
> array. Each one will have, say, two attributes, name and age. Some of  
> them may have other attributes in addition.
> 
> Note: I don’t need to have any methods, inheritance or any other  
> ‘class-ish’ behavior. Just the data.
> 
> Here are three representations. Which one will be faster? Which one will  
> be smaller?

Probably the hash representation, but what about an array of

[[name, age], …]

Can’t beat that for fast access, and storing a fixnum (age) in an array  
is particularly space-efficient (only 4 bytes for this field, per  
entry). Another option is the arrayfields gem, if you want array storage  
but keyword interface.

---

<div class="post-metadata">

**Author:** ![pitosalas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a4c791/32.png) [@pitosalas](https://www.ruby-forum.com/u/pitosalas)\
**Post date:** [July 13, 2009, 11:13pm UTC](https://www.ruby-forum.com/t/performance-question/172045/3 "2009-07-13T23:13:55Z")

</div>

On Monday 13 July 2009 15:15:16 Pito S. wrote:

> Here are three representations. Which one will be faster? Which one will  
> be smaller?

Thousands of records, each with two fields is a very small amount of  
data.

With “Name” and “Age” as an example, if you have a name like “Apu  
Nahasapeemapetilon” and set aside 4 bytes for the age, 100,000 records  
would  
take up roughly: 21+4 \* 100,000 =\> 25 \* 100,000 bytes, or 2.5 megabytes.  
There will be some overhead as well, but even if you double that to 5  
megabytes, it’s tiny by the standards of modern memory.

Speed will probably also not be a major issue. All you’re doing is  
looking up  
a value stored in memory.

Rather than worry too much about whether to use structures, objects or  
hashes  
for speed, why not choose the data type that makes the rest of the  
program  
easiest to write and to read. If later you decide it needs to be faster  
or  
smaller, you can adjust it, but unless you’re running on an embedded  
system,  
it’s unlikely you’ll have to.

Ben

---

<div class="post-metadata">

**Author:** ![pitosalas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a4c791/32.png) [@pitosalas](https://www.ruby-forum.com/u/pitosalas)\
**Post date:** [July 14, 2009, 3:23am UTC](https://www.ruby-forum.com/t/performance-question/172045/4 "2009-07-14T03:23:24Z")

</div>

Ben G. wrote:

> Rather than worry too much about whether to use structures, objects or  
> hashes for speed, why not choose the data type that makes the rest of the  
> program easiest to write and to read. If later you decide it needs to be  
> faster or smaller, you can adjust it, but unless you’re running on an  
> embedded system, it’s unlikely you’ll have to.

The example I gave was purposely oversimplified to make it easy to  
explain and understand. In reality the records will be far more complex  
and the numbers perhaps in the hundreds of thousands.

But still I do agree with you. I was just trying to see if one of the  
three choices was clearly brain dead or clearly the best one. Would  
using a hash repeat over and over the text of the keys (I assume ‘no’)  
or have far slower access? Would using a class that never would have a  
method incur a major performance overhead because accessing each value  
required a method call anyway?

- Pito

---

<div class="post-metadata">

**Author:** ![pitosalas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a4c791/32.png) [@pitosalas](https://www.ruby-forum.com/u/pitosalas)\
**Post date:** [July 14, 2009, 4:24am UTC](https://www.ruby-forum.com/t/performance-question/172045/5 "2009-07-14T04:24:46Z")

</div>

On Jul 13, 2009, at 21:23, Pito S. wrote:

> The example I gave was purposely oversimplified to make it easy to  
> explain and understand. In reality the records will be far more  
> complex  
> and the numbers perhaps in the hundreds of thousands.

Ok, well if you have an average number of bytes per record, you can  
probably guesstimate how much space each record will type.

> But still I do agree with you. I was just trying to see if one of the  
> three choices was clearly brain dead or clearly the best one. Would  
> using a hash repeat over and over the text of the keys (I assume ‘no’)

When you use a string (or anything else) as a hash key, Ruby  
uses .hash to figure out a hash key for it. The access time for  
people[“matz”].age should only be slightly slower than matz.age,  
because people[“matz”] has to find the hash value of “matz”, look up  
the value in the hash, then look up the data, whereas matz.age only  
has to look up the data.

I don’t know the internals of Ruby’s struct vs. class implementations,  
but they should be pretty similar.

> or have far slower access? Would using a class that never would have a  
> method incur a major performance overhead because accessing each value  
> required a method call anyway?

I’m not sure quite what you mean – a class that never would have a  
method? Do you mean a class that has no associated instance methods,  
other than the attribute accessors? If you mean the attribute  
accessor methods, it does add a tiny bit of overhead, but I’m pretty  
sure most of that is implemented in C. Whether the classes have  
additional methods associated (but never called) should not slow them  
down or add additional space per instance. If you never call the  
methods they’re just additional memory used once in the object  
definition. In memory, each unique instance of the class should just  
have the data associated with each instance of a class.

If you happen to tack an extra method onto one particular instance of  
a class, you’ll end up with unique method data for that one instance.

In other words, somewhere in memory you should have something like:

bob = Employee.new(“bob smith”, 42)  
ang = Employee.new(“angela carter”, 35)  
jj = Employee.new(“jason james”, 73)  
def jj.retired?  
true  
end

Employees:  
initialize: (name, age); @name = var, @age = age  
to\_s: “Name: #{name}, Age: #{age}”  
name: name  
name=: name = var  
age: age  
age=: age = var  
…

Data:  
{employee, bob smith, 42}  
{employee, angela carter, 35}  
{employee, jason james, 73, retired?: true}  
…

(I’m not completely sure how Ruby does the internals, esp instance  
methods on objects, but it should be something like that).

Overall, all three implementations you talked about should be  
relatively similar in speed and relatively similar in size. I think  
it’s easiest just to throw some sample data at them if you’re  
interested in how they perform. You can even use ObjectSpace to get  
an idea of the count of objects in memory at various points in your  
program.

Ben

---

<div class="post-metadata">

**Author:** ![pitosalas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a4c791/32.png) [@pitosalas](https://www.ruby-forum.com/u/pitosalas)\
**Post date:** [July 14, 2009, 6:09am UTC](https://www.ruby-forum.com/t/performance-question/172045/6 "2009-07-14T06:09:21Z")

</div>

On Monday 13 July 2009 08:23:26 pm Pito S. wrote:

> Would  
> using a hash repeat over and over the text of the keys (I assume ‘no’)

Definitely no, because it looks like you’re using symbols, not strings.  
In 1.8,  
at least, it should be roughly as efficient as using integers.

---

<div class="post-metadata">

**Author:** ![pitosalas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a4c791/32.png) [@pitosalas](https://www.ruby-forum.com/u/pitosalas)\
**Post date:** [July 14, 2009, 3:55am UTC](https://www.ruby-forum.com/t/performance-question/172045/7 "2009-07-14T03:55:15Z")

</div>

> Here are three representations. Which one will be faster? Which one will  
> be smaller?

My answer is try them each and find out 🙂  
I remember open structs using up a lot of memory, for some reason  
though.  
=r