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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:
return yield unless logger
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
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