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The Buckblog

assorted ramblings by Jamis Buck

Bulk Inserts in ActiveRecord

10 October 2015 — A new ActiveRecord extension is introduced, which enables efficient multi-row inserts — 2-minute read

This last week I finally sat down and scratched an itch that has been bothering me for some time. The result is called BulkInsert, and lets you insert multiple rows at a time using ActiveRecord.

Have you ever been in a situation where your app needs to insert dozens or hundreds (or thousands!) of rows at a time? Maybe it’s an importer, which needs to suck down a CSV or two, or a log processor, or a dictionary. Regardless, if you’ve ever found yourself doing this:

inputs.each do |input|
  Model.create(input)
end

you’ve probably noticed that it is not very fast. Wrapping it all in a transaction helps some:

Model.transaction do
  inputs.each do |input|
    Model.create(input)
  end
end

but it’s still not as fast as it might be. This is because it is creating one insert statement for each call to create:

INSERT INTO models (...) VALUES (...);
INSERT INTO models (...) VALUES (...);
INSERT INTO models (...) VALUES (...);
INSERT INTO models (...) VALUES (...);
...

But SQL lets you insert multiple rows in a single statement, using this syntax:

INSERT INTO models (...) VALUES
  (...),
  (...),
  (...),
  (...),
  ...

Sadly, no such feature exists for that in ActiveRecord natively. You have to drop down to SQL directly and build (and execute) the statement yourself…

But be of good cheer! Today, I introduce BulkInsert, a library for performing multi-row inserts! It works like this:

Model.bulk_insert do |worker|
  worker.add(...)
  worker.add(...)
  ...
end

Each item is added to the queue, and the whole is accumulated into a single insert at the end of the block. (For lots of rows, it might not actually be a single insert statement, though. Some backends, like SQLite, don’t like you to insert more than some number of rows at a time. For that reason, the worker will save up to 500 rows at a time by default, though you can change that set size if you need to.)

Give it a try and let me know what you think. It’s an itch that has bothered me for years, so hopefully others will find it useful, too.

Bulk Insert – Multi-Row Inserts for ActiveRecord