require 'active_support/core_ext/class/attribute' module ActiveRecord module Explain def self.extended(base) base.class_eval do # If a query takes longer than these many seconds we log its query plan # automatically. nil disables this feature. class_attribute :auto_explain_threshold_in_seconds, :instance_writer => false self.auto_explain_threshold_in_seconds = nil end end # If auto explain is enabled, this method triggers EXPLAIN logging for the # queries triggered by the block if it takes more than the threshold as a # whole. That is, the threshold is not checked against each individual # query, but against the duration of the entire block. This approach is # convenient for relations. # # The available_queries_for_explain thread variable collects the queries # to be explained. If the value is nil, it means queries are not being # currently collected. A false value indicates collecting is turned # off. Otherwise it is an array of queries. def logging_query_plan # :nodoc: threshold = auto_explain_threshold_in_seconds current = Thread.current if threshold && current[:available_queries_for_explain].nil? begin queries = current[:available_queries_for_explain] = [] start = Time.now result = yield logger.warn(exec_explain(queries)) if Time.now - start > threshold result ensure current[:available_queries_for_explain] = nil end else yield end end # Relation#explain needs to be able to collect the queries regardless of # whether auto explain is enabled. This method serves that purpose. def collecting_queries_for_explain # :nodoc: current = Thread.current original, current[:available_queries_for_explain] = current[:available_queries_for_explain], [] return yield, current[:available_queries_for_explain] ensure # Note that the return value above does not depend on this assigment. current[:available_queries_for_explain] = original end # Makes the adapter execute EXPLAIN for the tuples of queries and bindings. # Returns a formatted string ready to be logged. def exec_explain(queries) # :nodoc: queries && queries.map do |sql, bind| [].tap do |msg| msg << "EXPLAIN for: #{sql}" unless bind.empty? bind_msg = bind.map {|col, val| [col.name, val]}.inspect msg.last << " #{bind_msg}" end msg << connection.explain(sql, bind) end.join("\n") end.join("\n") end # Silences automatic EXPLAIN logging for the duration of the block. # # This has high priority, no EXPLAINs will be run even if downwards # the threshold is set to 0. # # As the name of the method suggests this only applies to automatic # EXPLAINs, manual calls to +ActiveRecord::Relation#explain+ run. def silence_auto_explain current = Thread.current original, current[:available_queries_for_explain] = current[:available_queries_for_explain], false yield ensure current[:available_queries_for_explain] = original end end end