How to efficiently process large Excel files using Ruby

Published in Ruby, Roo, Creek, ActiveRecord ImportComments

Last year, I worked on a project in which I needed to parse and handle large .xlsx files. Some of those files had more than 200K rows. I was looking for a gem that could efficiently do the job.

Process large excel files using Ruby

I wanted a simple solution that would just iterate over each row, parse the contents of the row and save data in database tables.

Popular gems in that time were Roo and Spreadsheet. I also found a simple gem called Simple xlsx reader that was easy to use and had everything I needed. Except one thing.

When I called SimpleXlsxReader.open(file_path), memory consumption would go to 2GB and it would stay that way until the garbage collector cleaned it.

What I needed was a library that would read Excel rows in streams. At that time, none of the mentioned gems had that ability. I found a gem called Creek that does only that - stream parsing large excel files. It is simple and works well. Memory consumption while parsing these files was now under 200 MB, which is acceptable. In the meantime, Roo was updated and now it has the same ability.

Also, to reduce the number of SQL queries, I implemented saving data in batches - 1000 rows in 1 query. So, my method reads a thousand rows, makes an array of ActiveRecord objects and then saves them at once. I used the gem called ActiveRecord Import for this purpose.

class ExcelDataParser
  def initialize(file_path)
    @file_path = file_path
    @records = []
    @counter = 1
  end

  BATCH_IMPORT_SIZE = 1000

  def call
    rows.each do |row|
      increment_counter
      records << build_new_record(row)
      import_records if reached_batch_import_size? || reached_end_of_file?
    end
  end

  private

  attr_reader :file_path, :records
  attr_accessor :counter

  def book
    @book ||= Creek::Book.new(file_path)
  end

  # in this example, we assume that the
  # content is in the first Excel sheet
  def rows
    @rows ||= book.sheets.first.rows
  end

  def increment_counter
    self.counter += 1
  end

  def row_count
    @row_count ||= rows.count
  end

  def build_new_record(row)
    # only build a new record without saving it
    RecordModel.new(...)
  end

  def import_records
    # save multiple records using activerecord-import gem
    RecordModel.import(records)

    # clear records array
    records.clear
  end

  def reached_batch_import_size?
    (counter % BATCH_IMPORT_SIZE).zero?
  end

  def reached_end_of_file?
    counter == row_count
  end
end

Finally, this task is being executed asynchronously in a background job since it's too heavy to handle in the web process.

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