I'm extracting some loading time data from a site into a HTTP ARchive format (HAR) file, but I just can't find what "_blocked_queueing" means.

_blocked_queueing in a har file

1 Answer 1


This may be of help to you:


A request being queued indicates that:

The request was postponed by the rendering engine because it's considered lower priority than critical resources (such as scripts/styles). This often happens with images.

The request was put on hold to wait for an unavailable TCP socket that's about to free up.

The request was put on hold because the browser only allows six TCP connections per origin on HTTP 1.

Time spent making disk cache entries (typically very quick.) Stalled/Blocking

Time the request spent waiting before it could be sent. It can be waiting for any of the reasons described for Queueing. Additionally, this time is inclusive of any time spent in proxy negotiation.

Queued or Stalled series The most common issue seen is a series of items that are queued or stalled. This indicates that too many resources are being retrieved from a single domain. On HTTP 1.0/1.1 connections, Chrome enforces a maximum of six TCP connections per host. If you are requesting twelve items at once, the first six will begin and the last half will be queued. Once one of the original half is finished, the first item in the queue will begin its request process.

Stalled series of requests

To fix this problem for traditional HTTP 1 traffic, you would need to implement domain sharding. That is making multiple subdomains on your application to serve resources from. Then split the resources being served evenly among the subdomains.

The fix for HTTP 1 connections does not apply to HTTP 2 connections. In fact, it hurts them. If you have HTTP 2 deployed, don’t domain-shard your resources as it works against how HTTP 2 is engineered to operate. In HTTP 2, there is a single TCP connection to the server that acts as a multiplexed connection. This gets rid of the six connection limit of HTTP 1 and multiple resources can be transferred over the single connection simultaneously.

source: https://developers.google.com/web/tools/chrome-devtools/network-performance/understanding-resource-timing#queued_or_stalled_series

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