Understanding Chrome network log “Stalled” state

Question

I've a following network log in chrome:

I don't understand one thing in it: what's the difference between filled gray bars and transparent gray bars.

Answer 1

DevTools: [network] explain empty bars preceeding request

Investigated further and have identified that there's no significant difference between our Stalled and Queueing ranges. Both are calculated from the delta's of other timestamps, rather than provided from netstack or renderer.

---

Currently, if we're waiting for a socket to become available:

• we'll call it stalled if some proxy negotiation happened
• we'll call it queuing if no proxy/ssl work was required.

Answer 2

My case is the page is sending multiple requests with different parameters when it was open. So most are being "stalled". Following requests immediately sent gets "stalled". Avoiding unnecessary requests would be better (to be lazy...).

Answer 3

Google gives a breakdown of these fields in the Evaluating network performance section of their DevTools documentation.

Excerpt from Resource network timing:

Stalled/Blocking

Time the request spent waiting before it could be sent. This time is inclusive of any time spent in proxy negotiation. Additionally, this time will include when the browser is waiting for an already established connection to become available for re-use, obeying Chrome's maximum six TCP connection per origin rule.

(If you forget, Chrome has an "Explanation" link in the hover tooltip and under the "Timing" panel.)

Basically, the primary reason you will see this is because Chrome will only download 6 files per-server at a time and other requests will be stalled until a connection slot becomes available.

This isn't necessarily something that needs fixing, but one way to avoid the stalled state would be to distribute the files across multiple domain names and/or servers, keeping CORS in mind if applicable to your needs, however HTTP2 is probably a better option going forward. Resource bundling (like JS and CSS concatenation) can also help to reduce amount of stalled connections.

Answer 4

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

This comes from the official site of Chome-devtools and it helps. Here i quote:

• Queuing If a request is queued it indicated 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.