Group items tagged

The slowms and sampleRate profiling settings are global. When set, these settings affect all databases in your process.

db.setProfilingLevel(1, { slowms: 20 })

db.setProfilingLevel(0, { slowms: 20 })

show profile

The system.profile collection is a capped collection with a default size of 1 megabyte.

By default, sampleRate is set to 1.0, meaning all slow operations are profiled.

When logLevel is set to 0, MongoDB records slow operations to the diagnostic log at a rate determined by slowOpSampleRate.

The slowms field indicates operation time threshold, in milliseconds, beyond which operations are considered slow.

You cannot enable profiling on a mongos instance.

profiler logs information about database operations in the system.profile collection.

each action also maps to particular CRUD operations in a database

One way to avoid deep nesting (as recommended above) is to generate the collection actions scoped under the parent, so as to get a sense of the hierarchy, but to not nest the member actions.

to only build routes with the minimal amount of information to uniquely identify the resource

The shallow method of the DSL creates a scope inside of which every nesting is shallow

These concerns can be used in resources to avoid code duplication and share behavior across routes

add a member route, just add a member block into the resource block

You can leave out the :on option, this will create the same member route except that the resource id value will be available in params[:photo_id] instead of params[:id].

Singular Resources

use a singular resource to map /profile (rather than /profile/:id) to the show action

Passing a String to get will expect a controller#action format

workaround

organize groups of controllers under a namespace

route /articles (without the prefix /admin) to Admin::ArticlesController

route /admin/articles to ArticlesController (without the Admin:: module prefix)

Nested routes allow you to capture this relationship in your routing.

Resources should never be nested more than 1 level deep.

via the :shallow option

a balance between descriptive routes and deep nesting

:shallow_path prefixes member paths with the specified parameter

Routing Concerns allows you to declare common routes that can be reused inside other resources and routes

Rails can also create paths and URLs from an array of parameters.

use url_for with a set of objects

In helpers like link_to, you can specify just the object in place of the full url_for call

insert the action name as the first element of the array

pass :on to a route, eliminating the block:

Collection Routes

simple routing makes it very easy to map legacy URLs to new Rails actions

add an alternate new action using the :on shortcut

When you set up a regular route, you supply a series of symbols that Rails maps to parts of an incoming HTTP request.

:controller maps to the name of a controller in your application

:action maps to the name of an action within that controller

This route will also route the incoming request of /photos to PhotosController#index, since :action and :id are

use a constraint on :controller that matches the namespace you require

dynamic segments don't accept dots

The params will also include any parameters from the query string

:defaults option.

set params[:format] to "jpg"

specify a name for any route using the :as option

create logout_path and logout_url as named helpers in your application.

Inside the show action of UsersController, params[:username] will contain the username for the user.

should use the get, post, put, patch and delete methods to constrain a route to a particular verb.

use the match method with the :via option to match multiple verbs at once

use the :constraints option to enforce a format for a dynamic segment

constraints

don't need to use anchors

the same name as the hash key and then compare the return value with the hash value.

constraint values should match the corresponding Request object method return type

blacklist

redirect helper

reuse dynamic segments from the match in the path to redirect

this redirection is a 301 "Moved Permanently" redirect.

root method

put the root route at the top of the file

root inside namespaces and scopes

For namespaced controllers you can use the directory notation

use the :constraints option to specify a required format on the implicit id

specify a single constraint to apply to a number of routes by using the block

non-resourceful routes

:id parameter doesn't accept dots

:as option lets you override the normal naming for the named route helpers

use the :as option to prefix the named route helpers that Rails generates for a rout

prevent name collisions

prefix routes with a named parameter

:only option

:except option

alter path names

http://localhost:3000/rails/info/routes

rake routes

setting the CONTROLLER environment variable

Routes should be included in your testing strategy

assert_generates assert_recognizes assert_routing

存取資料庫是一種相對很慢的I/O的操作：每一條SQL query都得耗上時間、執行回傳的結果也會被轉成ActiveRecord物件全部放進記憶體

如果需要撈出全部的資料做處理，強烈建議最好不要用all方法，因為這樣會把全部的資料一次放進記憶體中，如果資料有成千上萬筆的話，效能就墜毀了。

.find_each( :batch_size => 100 )

.find_in_batches( :batch_size => 100 )

在Transaction交易範圍內的SQL效能會加快，因為最後只需要COMMIT一次即可

Elasticsearch全文搜尋引擎和elasticsearch-rails gem

QueryReviewer這個套件透過SQL EXPLAIN分析SQL query的效率

必要時可以採用逆正規化的設計。犧牲空間，增加修改的麻煩，但是讓讀取這事件變得更快更簡單。

將成本轉嫁到寫入，而最佳化了讀取時間

在效能還沒有造成問題前，就為了優化效能而修改程式和架構，只會讓程式更混亂不好維護

當效能還不會造成問題時，程式的維護性比考慮效能重要

會拖慢整體效能的程式，只佔全部程式的一小部分而已，所以我們只最佳化會造成問題的程式。

善用分析工具找效能瓶頸，最佳化前需要測量，最佳化後也要測量比較。

rack-mini-profiler在頁面的左上角顯示花了多少時間，並且提供報表，推薦安裝

如果是不需要權限控管的靜態檔案，可以直接放在public目錄下讓使用者下載。

Web伺服器得先安裝好x_sendfile功能

如果要讓你的Assets例如CSS, JavaScript, Images也讓使用者透過CDN下載，只要修改config/environments/production.rb的config.action_controller.asset_host為CDN網址即可。

有時候「執行速度較快」的程式碼不代表好維護、好除錯的程式碼

Ruby不是萬能，有時候直接呼叫外部程式是最快的作法

globalLock.totalTime: If this is higher than the total database uptime, the database has been in a lock state for too long.

Unlike relational databases such as MySQL or PostgreSQL, MongoDB uses JSON-like documents for storing data.

Databases operate in an environment that consists of numerous reads, writes, and updates.

When a lock occurs, no other operation can read or modify the data until the operation that initiated the lock is finished.

locks.deadlockCount: Number of times the lock acquisitions have encountered deadlocks

Is the database frequently locking from queries? This might indicate issues with the schema design, query structure, or system architecture.

For version 3.2 on, WiredTiger is the default.

MMAPv1 locks whole collections, not individual documents.

When the MMAPv1 storage engine is in use, MongoDB will use memory-mapped files to store data.

db.serverStatus().mem

mem.resident: Roughly equivalent to the amount of RAM in megabytes that the database process uses

If mem.resident exceeds the value of system memory and there’s a large amount of unmapped data on disk, we’ve most likely exceeded system capacity.

If the value of mem.mapped is greater than the amount of system memory, some operations will experience page faults.

The WiredTiger storage engine is a significant improvement over MMAPv1 in performance and concurrency.

By default, MongoDB will reserve 50 percent of the available memory for the WiredTiger data cache.

wiredTiger.cache.bytes currently in the cache – This is the size of the data currently in the cache.

wiredTiger.cache.tracked dirty bytes in the cache – This is the size of the dirty data in the cache.

we can look at the wiredTiger.cache.bytes read into cache value for read-heavy applications. If this value is consistently high, increasing the cache size may improve overall read performance.

check whether the application is read-heavy. If it is, increase the size of the replica set and distribute the read operations to secondary members of the set.

Replication is the propagation of data from one node to another

Replication sets handle this replication.

Sometimes, data isn’t replicated as quickly as we’d like.

use the db.printSlaveReplicationInfo() or the rs.printSlaveReplicationInfo() command to see the status of a replica set from the perspective of the secondary member of the set.

shows how far behind the secondary members are from the primary. This number should be as low as possible.

monitor this metric closely.

watch for any spikes in replication delay.

One replica set is primary. All others are secondary.

use the profiler to gain a deeper understanding of the database’s behavior.

Enabling the profiler can affect system performance, due to the additional activity.

Microservices also bring a set of additional benefits, such as easier scaling, the possibility to use multiple programming languages and technologies, and others.

Java is a frequent choice for building a microservices architecture as it is a mature language tested over decades and has a multitude of microservices-favorable frameworks, such as legendary Spring, Jersey, Play, and others.

A monolithic architecture keeps it all simple. An app has just one server and one database.

All the connections between units are inside-code calls.

split our application into microservices and got a set of units completely independent for deployment and maintenance.

Each of microservices responsible for a certain business function communicates either via sync HTTP/REST or async AMQP protocols.

ensure seamless communication between newly created distributed components.

The gateway became an entry point for all clients’ requests.

We also set the Zuul 2 framework for our gateway service so that the application could leverage the benefits of non-blocking HTTP calls.

we've implemented the Eureka server as our server discovery that keeps a list of utilized user profile and order servers to help them discover each other.

We also have a message broker (RabbitMQ) as an intermediary between the notification server and the rest of the servers to allow async messaging in-between.

microservices can definitely help when it comes to creating complex applications that deal with huge loads and need continuous improvement and scaling.