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# frozen_string_literal: true
module Gitlab
module BackgroundMigration
module BatchingStrategies
# This strategy provides an efficient way to iterate over columns with non-distinct values.
# A common use case would be iterating over a foreign key columns, for example issues.project_id
class LooseIndexScanBatchingStrategy < BaseStrategy
include Gitlab::Database::DynamicModelHelpers
# Finds and returns the next batch in the table.
#
# table_name - The table to batch over
# column_name - The column to batch over
# batch_min_value - The minimum value which the next batch will start at
# batch_size - The size of the next batch
# job_arguments - The migration job arguments
# job_class - The migration job class
def next_batch(table_name, column_name, batch_min_value:, batch_size:, job_arguments:, job_class: nil)
model_class = define_batchable_model(table_name, connection: connection)
quoted_column_name = model_class.connection.quote_column_name(column_name)
relation = model_class.where("#{quoted_column_name} >= ?", batch_min_value)
next_batch_bounds = nil
relation.distinct_each_batch(of: batch_size, column: column_name) do |batch| # rubocop:disable Lint/UnreachableLoop
next_batch_bounds = batch.pluck(Arel.sql("MIN(#{quoted_column_name}), MAX(#{quoted_column_name})")).first
break
end
next_batch_bounds
end
end
end
end
end
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