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Guard Against Slow Queries with statement_timeout

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                  module StatementTimeout
  module_function

  def with_timeout(ms)
    ApplicationRecord.connection.execute("SET LOCAL statement_timeout = #{Integer(ms)}")
    yield
  ensure
    # SET LOCAL resets automatically at transaction end
  end
end

                  class SearchController < ApplicationController
  def index
    @results = ApplicationRecord.transaction do
      StatementTimeout.with_timeout(800) do
        Snip.search(params[:q]).limit(50)
      end
    end
  rescue ActiveRecord::QueryCanceled
    @results = []
    flash.now[:alert] = 'Search timed out. Please refine your query.'
  end
end

A per-request statement_timeout is a great “seatbelt” for endpoints that can run bad queries when parameters are unexpected. You can set it for a block; Postgres enforces the wall clock limit.

Sarah Chen

More from Sarah Chen

Guard Against Slow Queries with statement_timeout

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More from Sarah Chen