What does the times mean in Google Chrome's timeline in the network panel?

Question

Often when troubleshooting performance using the Google Chrome's network panel I see different times and often wonder what they mean.

Can someone validate that I understand these properly:

1. Blocking: Time blocked by browser's multiple request for the same domain limit(???)
2. Waiting: Waiting for a connection from the server (???)
3. Sending: Time spent to transfer the file from the server to the browser (???)
4. Receiving: Time spent by the browser analyzing and decoding the file (???)
5. DNS Lookup: Time spent resolving the hostname.
6. Connecting: Time spent establishing a socket connection.

Now how would someone fix long blocking times?

Now how would someone fix long waiting times?

Answer 1

Sending is time spent uploading the data/request to the server. It occurs between blocking and waiting. For example, if I post back an ASPX page this would indicate the amount of time it took to upload the request (including the values of the forms and the session state) back to the ASP server.

Waiting is the time after the request has been sent, but before a response from the server has been received. Basically this is the time spent waiting for a response from the server.

Receiving is the time spent downloading the response from the server.

Blocking is the amount of time between the UI thread starting the request and the HTTP GET request getting onto the wire.

The order these occur in is:

1. Blocking*
2. DNS Lookup
3. Connecting
4. Sending
5. Waiting
6. Receiving

*Blocking and DNS Lookup might be swapped.

The network tab does not indicate time spent processing.

If you have long blocking times then the machine running the browser is running slowly. You can fix this by upgrading the machine (more RAM, faster processor, etc.) or by reducing its workload (turn off services you do not need, closing programs, etc.).

Long wait times indicate that your server is taking a long time to respond to requests. This either means:

• The request takes a long time to process (like if you are pulling a large amount of data from the database, large amounts of data need to be sorted, or a file has to be found on an HDD which needs to spin up).
• Your server is receiving too many requests to handle all requests in a reasonable amount of time (it might take .02 seconds to process a request, but when you have 1000 requests there will be a noticeable delay).

The two issues (long waiting + long blocking) are related. If you can reduce the workload on the server by caching, adding new server, and reducing the work required for active pages then you should see improvements in both areas.

Answer 2

You can read a detailed official explanation from google team here. It is a really helpful resource and your info goes under Timeline view section.

Resource network timing shows the same information as in resource bar in timeline view. Answering your quesiton:

• DNS lookup: Time spent performing the DNS lookup. (you need to find out IP address of site.com and this takes time)
• Blocking: Time the request spent waiting for an already established connection to become available for re-use. As was said in another answer it does not depend on your server - this is client's problem.
• Connecting: Time it took to establish a connection, including TCP handshakes/retries, DNS lookup, and time connecting to a proxy or negotiating a secure-socket layer (SSL). Depends on network congestion.
• Sending - Time spent sending the request. Depends on the size of sent data (which is mostly small because your request is almost always a few bytes except if you submit a big image or huge amount of text), network congestion, proximity of client to server
• Waiting - Time spent waiting for the initial response. This is mostly the time of your server to process and respond to your response. This is how fast if your server calculating things, fetching records from database and so on.
• Receiving - Time spent receiving the response data. Something similar to the sending, but now you are getting your data from the server (response size is mostly bigger than request). So it also depends on the size, connection quality and so on.