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@palkan palkan/tracer.rb
Created Feb 13, 2020

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[GraphQL] verify batch load
# frozen_string_literal: true
module Graphql
# This module implements the functionality to track whether the batch loading is
# required for a field to solve N+1 problem.
#
# If you want to check whether a particular field doesn't use batch loading in vain,
# mark it with `verify_batch_load: true` option.
#
# By default, it logs the following information when detects a possible N+1 (thus, confirms that batch loading is required).
#
# To enable this tracer do the following:
# - extend the base field class, e.g. in BaseObject: `field_class.prepend(Graphql::BatchLoaderVerify::FieldExt)`
# - enabled tracer globally, i.e. in your schema: `tracer(Graphql::BatchLoaderVerify)`
# - OR per-query (e.g., if you want to add sampling): `execute(query, tracers: [Graphql::BatchLoaderVerify])`
module BatchLoaderVerify
module FieldExt
def initialize(*args, verify_batch_load: false, **kwargs, &block)
super(*args, **kwargs, &block)
@verify_batch_load = verify_batch_load
end
def to_graphql
super.tap do |new_field|
new_field.instance_variable_set(:@verify_batch_load, true) if @verify_batch_load
end
end
end
class << self
attr_accessor :reporter
STORE_KEY = :__blv_store__
def trace(event, metadata)
if event == "execute_query"
reset_store
store[:query] = metadata[:query].operation_name
yield.tap { report }
elsif event == "execute_field"
track(metadata[:path]) if metadata[:field].instance_variable_get(:@verify_batch_load)
yield
else
yield
end
end
def store
Thread.current[STORE_KEY] ||= {
paths: Hash.new { |h, k| h[k] = 0 },
}
end
def reset_store
Thread.current[STORE_KEY] = nil
end
def track(path)
store[:paths][normalize_path(path)] += 1
end
def normalize_path(path)
path.map { |segment| segment.is_a?(Numeric) ? "[]" : segment }.join(".").tap do |p|
p.gsub!(/\.\[\]/, "[]")
end
end
def report
batch_loadable_paths = store[:paths].select { |_, v| v > 1 }
return if batch_loadable_paths.empty?
batch_loadable_paths.each do |path, _|
reporter.call(store[:query], path)
end
end
end
self.reporter = lambda { |query, path|
Rails.logger.info "[query: #{query}] batch loading is required for #{path}"
}
end
end
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