Improve background workers

doc/cli.markdown

@@ -31,6 +31,7 @@ Available commands:
   cronjob                            Execute daily cronjob
   help                               Displays help for a command
   list                               Lists commands
+  worker                             Execute queue worker
  export
   export:daily-project-column-stats  Daily project column stats CSV export (number of tasks per column and per day)
   export:subtasks                    Subtasks CSV export
@@ -196,3 +197,9 @@ Note: Installed files will have the same permissions as the current user
 * Updating plugin: Budget Planning
 * Plugin up to date: Github Authentication
 ```
+
+### Run Background worker
+
+```bash
+./kanboard worker
+```

doc/index.markdown

@@ -105,7 +105,9 @@ Technical details
 
 ### Configuration
 
+- [Performances](performances.markdown)
 - [Daily background job](cronjob.markdown)
+- [Background Worker](worker.markdown)
 - [Config file](config.markdown)
 - [Environment variables](env.markdown)
 - [Email configuration](email-configuration.markdown)

doc/installation.markdown

@@ -53,13 +53,14 @@ The `.htaccess` is optional because its content can be included directly in the
 
 You can also define a custom location for the plugins and files folders by changing the [config file](config.markdown).
 
+Optional installation
+---------------------
+
+- Some features of Kanboard require that you run [a daily background job](cronjob.markdown) (Reports and analytics)
+- [Install the background worker](worker.markdown) to improve the performances
+
 Security
 --------
 
 - Don't forget to change the default user/password
-- Don't allow everybody to access to the directory `data` from the URL. There is already a `.htaccess` for Apache but nothing for Nginx.
-
-Notes
------
-
-- Some features of Kanboard require that you run [a daily background job](cronjob.markdown)
+- Don't allow everybody to access to the directory `data` from the URL. There is already a `.htaccess` for Apache but nothing for other web servers.

doc/performances.markdown

@@ -0,0 +1,39 @@
+Kanboard Performances
+=====================
+
+According to your configuration, some features can slow down the usage of Kanboard.
+By default, all operations are synchronous and performed in the same thread as the HTTP request.
+This is a PHP limitation.
+However, it's possible to improve that.
+
+Depending on the plugins you install, communicating to external services can take hundred of milliseconds or even seconds.
+To avoid blocking the main thread, it's possible to delegate these operations to a pool of [background workers](worker.markdown).
+This setup require that you install additional software in your infrastructure.
+
+How to detect the bottleneck?
+-----------------------------
+
+- Enable the debug mode
+- Monitor the log file
+- Do something in Kanboard (drag and drop a task for example)
+- All operations are logged with the execution time (HTTP requests, Email notifications, SQL requests)
+
+Improve Email notifications speed
+---------------------------------
+
+Using the SMTP method with an external server can be very slow.
+
+Possible solutions:
+
+- Use the background workers if you still want to use SMTP
+- Use a local email relay with Postfix and use the "mail" transport
+- Use an email provider that use an HTTP API to send emails (Sendgrid, Mailgun or Postmark)
+
+Improve Sqlite performances
+---------------------------
+
+Possible solutions:
+
+- Do not use Sqlite when you have a lot of concurrency (several users), choose Postgres or Mysql instead
+- Do not use Sqlite on a shared NFS mount
+- Do not use Sqlite on a disk with poor IOPS, it's always preferable to use local SSD drives

doc/worker.markdown

@@ -0,0 +1,35 @@
+Background Workers
+==================
+
+**This feature is experimental**.
+
+Depending on your configuration, some features can slow down the application if they are executed in the same process as the HTTP request.
+Kanboard can delegate these tasks to a background worker that listen for incoming events.
+
+Example of feature that may slow down Kanboard:
+
+- Sending emails via an external SMTP server can take several seconds
+- Sending notifications to external services
+
+This feature is optional and require the installation of a queue daemon on your server.
+
+### Beanstalk
+
+[Beanstalk](http://kr.github.io/beanstalkd/) is a simple, fast work queue.
+
+- To install Beanstalk, you can simply use the package manager of your Linux distribution
+- Install the [Kanboard plugin for Beanstalk](https://kanboard.net/plugin/beanstalk)
+- Start the worker with the Kanboard command line tool: `./kanboard worker`
+
+### RabbitMQ
+
+[RabbitMQ](https://www.rabbitmq.com/) is a robust messaging system that is more suitable for high-availability infrastructure.
+
+- Follow the official documentation of RabbitMQ for the installation and the configuration
+- Install the [Kanboard plugin for RabbitMQ](https://kanboard.net/plugin/rabbitmq)
+- Start the worker with the Kanboard command line tool: `./kanboard worker`
+
+### Notes
+
+- You should start the Kanboard worker with a process supervisor (systemd, upstart or supervisord)
+- The process must be have access to the data folder if you store files on the local filesystem and have Sqlite