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: Performance of ActiveRecord-Setters ยท GitHub
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
