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translating Asynchronism to Brazilian Portuguese #22

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@ -142,9 +142,9 @@ Interested in **translating**? Please see the following [ticket](https://github
* [Write-through](#write-through) * [Write-through](#write-through)
* [Write-behind (write-back)](#write-behind-write-back) * [Write-behind (write-back)](#write-behind-write-back)
* [Refresh-ahead](#refresh-ahead) * [Refresh-ahead](#refresh-ahead)
* [Asynchronism](#asynchronism) * [Assincronismo](#assincronismo)
* [Message queues](#message-queues) * [Filas de Mensagens](#fila-de-mensagens)
* [Task queues](#task-queues) * [Fila de Tarefas](#fila-de-tarefas)
* [Back pressure](#back-pressure) * [Back pressure](#back-pressure)
* [Communication](#communication) * [Communication](#communication)
* [Transmission control protocol (TCP)](#transmission-control-protocol-tcp) * [Transmission control protocol (TCP)](#transmission-control-protocol-tcp)
@ -379,7 +379,7 @@ First, you'll need a basic understanding of common principles, learning about wh
* [Clones](http://www.lecloud.net/post/7295452622/scalability-for-dummies-part-1-clones) * [Clones](http://www.lecloud.net/post/7295452622/scalability-for-dummies-part-1-clones)
* [Databases](http://www.lecloud.net/post/7994751381/scalability-for-dummies-part-2-database) * [Databases](http://www.lecloud.net/post/7994751381/scalability-for-dummies-part-2-database)
* [Caches](http://www.lecloud.net/post/9246290032/scalability-for-dummies-part-3-cache) * [Caches](http://www.lecloud.net/post/9246290032/scalability-for-dummies-part-3-cache)
* [Asynchronism](http://www.lecloud.net/post/9699762917/scalability-for-dummies-part-4-asynchronism) * [Assincronismo](http://www.lecloud.net/post/9699762917/scalability-for-dummies-part-4-asynchronism)
### Next steps ### Next steps
@ -1261,7 +1261,7 @@ Refresh-ahead can result in reduced latency vs read-through if the cache can acc
* [AWS ElastiCache strategies](http://docs.aws.amazon.com/AmazonElastiCache/latest/UserGuide/Strategies.html) * [AWS ElastiCache strategies](http://docs.aws.amazon.com/AmazonElastiCache/latest/UserGuide/Strategies.html)
* [Wikipedia](https://en.wikipedia.org/wiki/Cache_(computing)) * [Wikipedia](https://en.wikipedia.org/wiki/Cache_(computing))
## Asynchronism ## Assincronismo
<p align="center"> <p align="center">
<img src="http://i.imgur.com/54GYsSx.png"> <img src="http://i.imgur.com/54GYsSx.png">
@ -1269,43 +1269,42 @@ Refresh-ahead can result in reduced latency vs read-through if the cache can acc
<i><a href=http://lethain.com/introduction-to-architecting-systems-for-scale/#platform_layer>Source: Intro to architecting systems for scale</a></i> <i><a href=http://lethain.com/introduction-to-architecting-systems-for-scale/#platform_layer>Source: Intro to architecting systems for scale</a></i>
</p> </p>
Asynchronous workflows help reduce request times for expensive operations that would otherwise be performed in-line. They can also help by doing time-consuming work in advance, such as periodic aggregation of data. Tarefas assíncronas ajudam a reduzir o tempo de uma requisição em operações assíncronas que por outro lado seriam executadas sincronamente. Elas também podem te ajudar adiantando tarefas que são demoradas, como agregação periódica de dados.
### Message queues ### Fila de Mensagens
Message queues receive, hold, and deliver messages. If an operation is too slow to perform inline, you can use a message queue with the following workflow: Filas de mensagens recebem, mantém, e entregam mensagens. Se uma operação é muito lenta para ser executada sequencialmente, você pode usar uma fila de mensagens da seguinte forma:
* An application publishes a job to the queue, then notifies the user of job status * Uma aplicação adiciona uma tarefa na fila, e notifica o usuário do estado da tarefa.
* A worker picks up the job from the queue, processes it, then signals the job is complete * Um worker pega a tarefa da fila, processa e notifica que a tarefa foi concluída.
The user is not blocked and the job is processed in the background. During this time, the client might optionally do a small amount of processing to make it seem like the task has completed. For example, if posting a tweet, the tweet could be instantly posted to your timeline, but it could take some time before your tweet is actually delivered to all of your followers. O usuário não é interrompido e a tarefa é processada em background. Durante esse tempo, a aplicação cliente pode opcionalmente fazer algum processamento para parecer que a tarefa foi concluída. Por exemplo, se estiver postando um tweet, o tweet poderia ser instantaneamente postado na sua linha do tempo, mas poderia levar um tempo a mais para que o tweet seja realmente entrege para todos os seus seguidores.
**Redis** is useful as a simple message broker but messages can be lost. **Redis** é util como um simples **message broker** mas as mensagens podem se perder.
**RabbitMQ** is popular but requires you to adapt to the 'AMQP' protocol and manage your own nodes. **RabbitMQ** é popular mas requer que você use o protocolo AMQP e gerencie seus própios nós.
**Amazon SQS**, é servido pela Amazon mas pode ter uma latência grande e existe a possibilidade das mensagens serem entreges duas vezes.
**Amazon SQS**, is hosted but can have high latency and has the possibility of messages being delivered twice. ### Fila de tarefas
### Task queues Filas de tarefas recebem tarefas e dados relacionados a elas, executam e retornam os resultados. Filas de tarefas podem suportar agendamento de tarefas e podem ser usadas para executar tarefas que são computacionalmente intensivas em background.
Tasks queues receive tasks and their related data, runs them, then delivers their results. They can support scheduling and can be used to run computationally-intensive jobs in the background. **Celery** possui suporte para agendamento de tarefas e é usado para executar programas python.
**Celery** has support for scheduling and primarily has python support.
### Back pressure ### Back pressure
If queues start to grow significantly, the queue size can become larger than memory, resulting in cache misses, disk reads, and even slower performance. [Back pressure](http://mechanical-sympathy.blogspot.com/2012/05/apply-back-pressure-when-overloaded.html) can help by limiting the queue size, thereby maintaining a high throughput rate and good response times for jobs already in the queue. Once the queue fills up, clients get a server busy or HTTP 503 status code to try again later. Clients can retry the request at a later time, perhaps with [exponential backoff](https://en.wikipedia.org/wiki/Exponential_backoff). Se as filas começarem a crescer significantemente, o tamanho da fila pode se tornar maior que a quantidade de memória disponível, resultando em cache misses, acesso ao disco e até degradação da perfomance. [Back pressure](http://mechanical-sympathy.blogspot.com/2012/05/apply-back-pressure-when-overloaded.html) pode ajudar limitando o tamanho da fila, desse modo mantendo uma alta taxa de vazão e bom tempo de resposta para tarefas que já estão na fila. Uma vez que a fila enche, a aplicação cliente recebe um status HTTP 503 informando que o servidor está ocupado e que a aplicação cliente deveria tentar novamente mais tarde, talvez com [exponential backoff](https://en.wikipedia.org/wiki/Exponential_backoff).
### Disadvantage(s): asynchronism ### Desvantagen(s): Assincronismo
* Use cases such as inexpensive calculations and realtime workflows might be better suited for synchronous operations, as introducing queues can add delays and complexity. * Casos de uso como cálculos que não são custosos ou operações em tempo real podem ser melhor em operações síncronas, sendo que adicionar filas pode adcionar atrasos e complexidade.
### Source(s) and further reading ### Fonte(s) e leituras adicionais
* [It's all a numbers game](https://www.youtube.com/watch?v=1KRYH75wgy4) * [É tudo um jogo de números - Em inglês](https://www.youtube.com/watch?v=1KRYH75wgy4)
* [Applying back pressure when overloaded](http://mechanical-sympathy.blogspot.com/2012/05/apply-back-pressure-when-overloaded.html) * [Aplicando back pressure quando sobrecarregado - Em inglês](http://mechanical-sympathy.blogspot.com/2012/05/apply-back-pressure-when-overloaded.html)
* [Little's law](https://en.wikipedia.org/wiki/Little%27s_law) * [Lei de Little - Em Inglês](https://en.wikipedia.org/wiki/Little%27s_law)
* [What is the difference between a message queue and a task queue?](https://www.quora.com/What-is-the-difference-between-a-message-queue-and-a-task-queue-Why-would-a-task-queue-require-a-message-broker-like-RabbitMQ-Redis-Celery-or-IronMQ-to-function) * [Qual é a diferença entre uma fila de mensagens e uma fila de tarefas? - Em inglês](https://www.quora.com/What-is-the-difference-between-a-message-queue-and-a-task-queue-Why-would-a-task-queue-require-a-message-broker-like-RabbitMQ-Redis-Celery-or-IronMQ-to-function)
## Communication ## Communication