AZ Asia-Pacific - Zscaler Help Centre
All Categories Zscaler Internet Access Analyzing Web Request

Analyzing Web Request

Analyzing Web Requests

The steps taken to analyze the Web Requests captured by HAR file varies depending on the troubleshooting Performance Issue or Page Rendering issue.

A common tool that is used to view the HAR files generated is HAR Viewer which is available as a Web Application.

Troubleshooting Performance Issues

The interested information for Performance issue is the load time and which request is causing the delay on the browser to serve the content to the user. So an understanding towards the definitions used for Web Request is required for effective troubleshooting, see below:

The below is extracted from HAR file loaded in HAR Viewer or Google's tool, HAR Analyzer.

Highlighting any web request after loading the HAR file will reveal the information below:

Request start time since the beginning

The highlighted request is called after how long from the initial request. Example: Like below +6.32s means the current request is being called after 6.32 seconds after the initial request (Most of the time HTML request as the initial one)

Waiting

Amount of time waiting for the Server to respond. If this value is high, it could mean:

  1. If the time waiting is low locally then the networks between your client and the server are the problem. The network traversal could be hindered by any number of things. There are a lot of points between clients and servers and each one has its own connection limitations and could cause a problem. The simplest method to test reducing this is to put your application on another host and see if the time waiting improves.

  2. That the server is busy or suffering a performance issue.Below we can see that there is around 2 seconds wait time from the server; this scenario was due to a complex jql query:

Typically when in this situation, cross check for any heavy running tasks (Example : Creating Backup, Reindex).

If this is always seen during a specific time of the day, record the time of occurrence and create support ticket at support.atlassian.com for assistance on identifying the root cause.

Receiving

This one is the amount of time used for the server to transfer the required information to the client. Typically this is the where we detect is a network issue. See below for an example:


This example above has a 1.6 seconds wait time, which took most of the delay for the request to complete.

DOM Loaded

DOM loaded means that all the HTML has been received and parsed by the browser into the DOM tree which can now be manipulated.

It occurs before the page has been fully rendered (as external resources may have not yet fully downloaded - including images, CSS, JavaScript and any other linked resources).

 Do not confuse with onload event:

The onload event occurs when an object has been loaded. onload is most often used within the <body> element to execute a script once a web page has completely loaded all content (including images, script files, CSS files, etc.).

The onload event can be used to check the visitor's browser type and browser version, and load the proper version of the web page based on the information.

Ref: http://www.w3schools.com/jsref/event_onload.asp

Page Loaded

Total time taken for the page to be fully loaded. (Inclusive of AJAX call or any REST call from javascript to populate data on external server: Example, google analytics)

It does not means that the page is white without any content until the page is fully loaded, the page normally will show after the onload event, after that it will populate the information from the external call. Such as Dashboard Gadget when loading:


Is you have external resources to populate the page (Gadgets, external links) It could take a longer time to completely load the page, however it is not depending on the performance of the server but rather the speed to handle the request from other site/server.

Size

The size of the request being served plays a role on performance issue as well, for better understanding on how it contributes to delay:

How long will it take to serve the 2.4MB data? A calculation is shown below:

3Mbps = Approximate 0.375MBps (note: B = byte, b = bit)

In order to get 2.4MB, you will need:

2.4MB/0.375MBps = 6.4 seconds

And this depends on the throughput available, generally can run a Speed Test and check the throughput to server nearest to the hosting datacenter.

A similar view is obtained by viewing the Network tab on respective browser types listed above. 

Steps to analyse is very straight forward if the above definition is clearly understood:

  1. Search for the delay responding request (typically the longest bar viewing the total web requests)

  2. Identify what is the longest waiting time, and how long it waited

  3. Check what is the main contributor towards the delay (Blocking, Waiting or Receiving)

  4. Run consistency checking by reloading the page multiple time

  5. Seek for assistance from the Support team with the information captured if identifying the Server is contributing the delay. For other issues, such as network, it is faster to reach out directly to the ISP or internal hosting team for assistance. The information gathered should be suffice to show the observation.

Troubleshooting Rendering Issue

In common cases, when a page fails to render correctly, the cause should be logged in the Console tab from the Developer Tools. If no reason is logged, try disabling the browser cache by checking the box next to Disable Cache. This will force the browser to render the page from scratch instead of using cached data. Similarly the status code from the HAR file can also help to identify which request could have caused the issue.

Example for some error message seen in Console tab accompany the code of 404 Bad Request:

{"errorMessages":["Error in JQL Query: Expecting either a value, list or function but got 'IN'. You must surround 'IN' in quotation marks to use it as a value. (line 1, character 11)"],"errors":{}}

This is found from the bug  JRACLOUD-65837 - Creating a project using Reserved Words of JQL as project key breaks the new project navigation issue view CLOSED  which is also a page rendering issue

It is important to be able to identify the status code from the HAR files generated as well. Below is few of the common example:

  • 200 - Success

  • 404 - Page not found / Bad Request

  • 401 - Unauthorized

  • 403 - Forbidden 

  • 304 - Not Modified (Content is cached)

  • 500 - Internal Server Error

For the definition of the error, you can refer to the HTTP/1.1 Status Code Definition page for detail.

After capturing the consistent behaviour, provide this information to the support team together with the steps taken for the Support team to work on potential cause behind the observation.