Rails core - Oct 2012 - ActiveRecord setter performance

I recently did a batch-processing operation, which simulated a calculation 
with roughly 80''000 ActiveRecord objects. Since it was just a
simulation
none of the records were actually persisted to the database. The 
performance of the operation was pretty bad and I investigated a bit. I 
could resolve most of the performance issues by replacing the use of 
ActiveRecord setters with instance variables. I was a bit confused though 
that AR-setters have such a huge impact on performance. I created a gist 
with a test-case that replicated my 
findings: https://gist.github.com/3965012

I don''t know the ActiveRecord source that well and wanted to ask what
the
primary reason for the bad performance is. Is there a way to optimize it?

Cheers,
-- Yves

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On Sat, Oct 27, 2012 at 9:53 PM, Yves Senn <yves.senn@gmail.com>
wrote:
> I recently did a batch-processing operation, which simulated a calculation
> with roughly 80''000 ActiveRecord objects. Since it was just a
simulation
> none of the records were actually persisted to the database. The
performance
> of the operation was pretty bad and I investigated a bit. I could resolve
> most of the performance issues by replacing the use of ActiveRecord setters
> with instance variables. I was a bit confused though that AR-setters have
> such a huge impact on performance. I created a gist with a test-case that
> replicated my findings: https://gist.github.com/3965012
>
The continuing update of an attribute seems to slow down the actions performed.
A single "data.big_bank_balance += i" leads to calls to
read_attribute[1], write_attribute[2],
column casting{both for read and write}, amongst other things, even if
the value wasn''t being persisted.
Since the attribute was being rewritten again and again, it was also
being deleted from the attributes cache.
> I don''t know the ActiveRecord source that well and wanted to ask
what the
> primary reason for the bad performance is. Is there a way to optimize it?
>
Just a thought, but shouldn''t ideally batch actions/ or similar ones
be isolated from "ActiveRecord" , and performed
outside instead of polluting this pattern?
> Cheers,
> -- Yves
>
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[1]
https://github.com/rails/rails/blob/master/activerecord/lib/active_record/attribute_methods/read.rb#L82
[2]
https://github.com/rails/rails/blob/master/activerecord/lib/active_record/attribute_methods/write.rb#L30

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