Merge pull request #6815 from softark/docs-guide-tutorial-performance

docs/guide/tutorial-performance-tuning.md better wordings[ci skip]

docs/guide/tutorial-performance-tuning.md

@@ -14,7 +14,7 @@ Preparing environment
 
 A well configured environment to run PHP application really matters. In order to get maximum performance:
 
-- Always use latest stable PHP version. Each major release brings significant performance improvements and reduced
+- Always use the latest stable PHP version. Each major release brings significant performance improvements and reduced
   memory usage.
 - Use [APC](http://ru2.php.net/apc) for PHP 5.4 and less or [Opcache](http://php.net/opcache) for PHP 5.5 and more. It
   gives a very good performance boost.
@@ -26,8 +26,8 @@ Preparing framework for production
 
 First thing you should do before deploying your application to production environment
 is to disable debug mode. A Yii application runs in debug mode if the constant
-`YII_DEBUG` is defined as `true` in `index.php` so to disable debug the following
+`YII_DEBUG` is defined as `true` in `index.php`.
-should be in your `index.php`:
+So, in order to disable debug mode, the following should be in your `index.php`:
 
 ```php
 defined('YII_DEBUG') or define('YII_DEBUG', false);
@@ -43,7 +43,7 @@ Enabling the PHP opcode cache improves any PHP application performance and lower
 memory usage significantly. Yii is no exception. It was tested with both
 [PHP 5.5 OPcache](http://php.net/manual/en/book.opcache.php) and
 [APC PHP extension](http://php.net/manual/en/book.apc.php). Both cache
-and optimize PHP intermediate code and avoid the time spent in parsing PHP
+optimize PHP intermediate code and avoid the time spent in parsing PHP
 scripts for every incoming request.
 
 ### Turning on ActiveRecord database schema caching
@@ -90,7 +90,7 @@ In order to learn how it can be achieved, refer to [assets](structure-assets.md)
 ### Using better storage for sessions
 
 By default PHP uses files to handle sessions. It is OK for development and
-small projects but when it comes to handling concurrent requests it's better to
+small projects. But when it comes to handling concurrent requests, it's better to
 switch to another storage such as database. You can do so by configuring your
 application via `config/web.php`:
 
@@ -101,11 +101,11 @@ return [
         'session' => [
             'class' => 'yii\web\DbSession',
 
-            // Set the following if want to use DB component other than
+            // Set the following if you want to use DB component other than
             // default 'db'.
             // 'db' => 'mydb',
 
-            // To override default session table set the following
+            // To override default session table, set the following
             // 'sessionTable' => 'my_session',
         ],
     ],
@@ -114,7 +114,7 @@ return [
 
 You can use `CacheSession` to store sessions using cache. Note that some
 cache storage such as memcached has no guarantee that session data will not
-be lost leading to unexpected logouts.
+be lost, and it would lead to unexpected logouts.
 
 If you have [Redis](http://redis.io/) on your server, it's highly recommended as session storage.
 
@@ -132,7 +132,7 @@ If a whole page remains relative static, we can use the page caching approach to
 save the rendering cost for the whole page.
 
 
-### Leveraging HTTP to save processing time and bandwidth
+### Leveraging HTTP caching to save processing time and bandwidth
 
 Leveraging HTTP caching saves both processing time, bandwidth and resources significantly. It can be implemented by
 sending either `ETag` or `Last-Modified` header in your application response. If browser is implemented according to
@@ -211,7 +211,7 @@ In the view you should access fields of each individual record from `$posts` as
 
 ```php
 foreach ($posts as $post) {
-    echo $post['title']."<br>";
+    echo $post['title'] . "<br>";
 }
 ```
 
@@ -225,12 +225,12 @@ request later if there's no need for immediate response.
 
 There are two common ways to achieve it: cron job processing and specialized queues.
 
-In the first case we need to save data which processing we want to do later to persistent storage
+In the first case we need to save the data that we want to process later to a persistent storage
 such as database. A [console command](tutorial-console.md) that is run regularly via cron job queries
 database and processes data if there's any.
 
 The solution is OK for most cases but has one significant drawback. We aren't aware if there's data to
-process before we query database so we're either querying database quite often or have a slight delay
+process before we query database, so we're either querying database quite often or have a slight delay
 between each data processing.
 
 This issue could be solved by queue and job servers such RabbitMQ, ActiveMQ, Amazon SQS and more.