rails的query cache
跟踪一下两次查询所使用的query cache
class StudentsController < ApplicationController
def show
id = params[:id]
@student =binding.trace_tree(htmp: 'ar/query_cache') do
Student.find id
Student.find id
end
end
end然后执行
[2] pry(main)> app.get '/students/2'
Started GET "/students/2" for 127.0.0.1 at 2017-11-15 21:57:28 +0800
(0.1ms) SELECT "schema_migrations"."version" FROM "schema_migrations" ORDER BY "schema_migrations"."version" ASC
Processing by StudentsController#show as HTML
Parameters: {"id"=>"2"}
Student Load (75.4ms) SELECT "students".* FROM "students" WHERE "students"."id" = ? LIMIT ? [["id", 2], ["LIMIT", 1]]
CACHE Student Load (25.6ms) SELECT "students".* FROM "students" WHERE "students"."id" = ? LIMIT ? [["id", 2], ["LIMIT", 1]]
Rendering students/show.html.erb within layouts/application
Rendered students/show.html.erb within layouts/application (5.4ms)得调用栈如下
检查第二个find，可看到cached_find_by_statement、StatementCache、cache_sql、query_cache.rb这些字眼。这个过程经历的代码大概如下
activerecord-5.1.4/lib/active_record/core.rb
def cached_find_by_statement(key, &block)
cache = @find_by_statement_cache[connection.prepared_statements]
cache[key] || cache.synchronize {
cache[key] ||= StatementCache.create(connection, &block)
}
endactiverecord-5.1.4/lib/active_record/statement_cache.rb
def execute(params, klass, connection, &block)
bind_values = bind_map.bind params
sql = query_builder.sql_for bind_values, connection
klass.find_by_sql(sql, bind_values, preparable: true, &block)
endactiverecord-5.1.4/lib/active_record/connection_adapters/abstract/query_cache.rb
def select_all(arel, name = nil, binds = [], preparable: nil)
if @query_cache_enabled && !locked?(arel)
arel, binds = binds_from_relation arel, binds
sql = to_sql(arel, binds)
cache_sql(sql, name, binds) { super(sql, name, binds, preparable: preparable) }
else
super
end
end
private
def cache_sql(sql, name, binds)
@lock.synchronize do
result =
if @query_cache[sql].key?(binds)
ActiveSupport::Notifications.instrument(
"sql.active_record",
sql: sql,
binds: binds,
name: name,
connection_id: object_id,
cached: true,
)
@query_cache[sql][binds]
else
@query_cache[sql][binds] = yield
end
result.dup
end
end在query_cache.rb中，调用cache_sql的就只有select_all，莫非所有查询最终都会去到select_all？
于是尝试一个稍微复杂的sql
[4] pry(main)> binding.trace_tree(htmp: 'ar/joins'){ Human.joins(:cells, :spirit).where('cells.id >= 18').to_a }
Human Load (31.3ms) SELECT "humen".* FROM "humen" INNER JOIN "cells" ON "cells"."human_id" = "humen"."id" INNER JOIN "spirits" ON "spirits"."human_id" = "humen"."id" WHERE (cells.id >= 18)
=> [#<human:0x007f3f2bab5c18 id:="" 9,="" name:="" "ken",="" created_at:="" sun,="" 05="" nov="" 2017="" 13:07:10="" utc="" +00:00,="" updated_at:="" tue,="" 07="" nov="" 2017="" 14:06:53="" utc="" +00:00="">,
#<human:0x007f3f2f286638 id:="" 9,="" name:="" "ken",="" created_at:="" sun,="" 05="" nov="" 2017="" 13:07:10="" utc="" +00:00,="" updated_at:="" tue,="" 07="" nov="" 2017="" 14:06:53="" utc="" +00:00="">]</human:0x007f3f2f286638></human:0x007f3f2bab5c18>完整调用栈如下
确实是的
那么@query_cache_enabled是怎么设为true的呢？为了得知，加入puts caller
module ActiveRecord
module ConnectionAdapters
module QueryCache
def enable_query_cache!
puts caller
@query_cache_enabled = true
end再rails s访问，得
Started GET "/students/2" for 192.168.0.103 at 2017-11-15 23:42:01 +0800
Cannot render console from 192.168.0.103! Allowed networks: 127.0.0.1, ::1, 127.0.0.0/127.255.255.255
Processing by StudentsController#show as HTML
Parameters: {"id"=>"2"}
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/query_cache.rb:131:in `configure_query_cache!'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:413:in `block in make_lambda'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:270:in `block in simple'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:511:in `block in invoke_after'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:511:in `each'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:511:in `invoke_after'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:132:in `run_callbacks'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:827:in `_run_checkout_callbacks'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:807:in `checkout_and_verify'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:500:in `checkout'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:374:in `connection'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:931:in `retrieve_connection'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/connection_handling.rb:116:in `retrieve_connection'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/connection_handling.rb:88:in `connection'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/core.rb:301:in `cached_find_by_statement'
/home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/core.rb:183:in `find'
# ...这里获取数据库连接的checkout方法，已在query_cache.rb中定义了configure_query_cache!的callback
def connection
@thread_cached_conns[connection_cache_key(@lock_thread || Thread.current)] ||= checkout
end
def checkout(checkout_timeout = @checkout_timeout)
checkout_and_verify(acquire_connection(checkout_timeout))
end
def checkout_and_verify(c)
c._run_checkout_callbacks do
c.verify!
end
c
rescue
remove c
c.disconnect!
raise
end那么，为什么在console直接查询（非app.get ...）又没有query cache呢？
首先，回调configure_query_cache!是根据connection_pool是否query_cache_enabled来设置connection的enable_query_cache的
# activerecord-5.1.4/lib/active_record/connection_adapters/abstract/query_cache.rb
def configure_query_cache!
enable_query_cache! if pool.query_cache_enabled
end而connection_pool所include的ConnectionPoolConfiguration要靠有人调用enable_query_cache!来设置缓存开关
# activerecord-5.1.4/lib/active_record/connection_adapters/abstract/query_cache.rb
module ActiveRecord
module ConnectionAdapters
module QueryCache
module ConnectionPoolConfiguration
def enable_query_cache!
@query_cache_enabled[connection_cache_key(Thread.current)] = true
connection.enable_query_cache! if active_connection?
end
def query_cache_enabled
@query_cache_enabled[connection_cache_key(Thread.current)]
end
end搜索一下enable_query_cache!，会发现它是hook的
# activerecord-5.1.4/lib/active_record/query_cache.rb
module ActiveRecord
class QueryCache
def self.run
caching_pool = ActiveRecord::Base.connection_pool
caching_was_enabled = caching_pool.query_cache_enabled
caching_pool.enable_query_cache!
[caching_pool, caching_was_enabled]
end
def self.install_executor_hooks(executor = ActiveSupport::Executor)
executor.register_hook(self)
end
end
end于是，在run中加入puts caller，再次rails c并app.get
[1] pry(main)> app.get '/students/2' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/execution_wrapper.rb:25:in `before' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:413:in `block in make_lambda' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:197:in `block (2 levels) in halting' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:601:in `block (2 levels) in default_terminator' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:600:in `catch' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:600:in `block in default_terminator' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:198:in `block in halting' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:507:in `block in invoke_before' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:507:in `each' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:507:in `invoke_before' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/callbacks.rb:130:in `run_callbacks' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/execution_wrapper.rb:108:in `run!' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/execution_wrapper.rb:70:in `block in run!' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/execution_wrapper.rb:67:in `tap' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.4/lib/active_support/execution_wrapper.rb:67:in `run!' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/actionpack-5.1.4/lib/action_dispatch/middleware/executor.rb:10:in `call' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/actionpack-5.1.4/lib/action_dispatch/middleware/static.rb:125:in `call' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/rack-2.0.3/lib/rack/sendfile.rb:111:in `call' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/railties-5.1.4/lib/rails/engine.rb:522:in `call' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/rack-test-0.7.0/lib/rack/mock_session.rb:30:in `request' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/rack-test-0.7.0/lib/rack/test.rb:249:in `process_request' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/rack-test-0.7.0/lib/rack/test.rb:125:in `request' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/actionpack-5.1.4/lib/action_dispatch/testing/integration.rb:261:in `process' /home/z/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/actionpack-5.1.4/lib/action_dispatch/testing/integration.rb:16:in `get' (pry):1:in `'
可以看出这个回调在某层middleware被触发
# actionpack-5.1.4/lib/action_dispatch/middleware/executor.rb
module ActionDispatch
class Executor
def initialize(app, executor)
@app, @executor = app, executor
end
def call(env)
state = @executor.run!
begin
response = @app.call(env)
returned = response << ::Rack::BodyProxy.new(response.pop) { state.complete! }
ensure
state.complete! unless returned
end
end
end
end因此，只有经过rack才会设置query cache，单单在console中是没打开这一功能的（当然手动enable是可以）