Salesforce says

Maximum simultaneous requests to URLs with the same host for a callout request is 20

Statement is very simple to read but it is not very clear as to what it means. Can anyone explain what this statement means and how can i reproduce this exception in my Sandbox?

Once more thing what is the difference between simultaneous and concurrent? Are both same or different?


I looked at the salesforce documentation.

Maximum simultaneous requests to URLs with the same host for a callout request is 20

Simultaneous means starting at the same time while concurrent means running parallel (may not be started at same time.). Example your Sales-force org will have many concurrent sessions as most of users are using salesforce but it is highly unlikely that all of the have logged in at same instant/simultaneously.

Since the lifetime of a request is very short(Public sites) hence you can consider both concurrent and simultaneous as same.

From Sales-force Documentation:

The host is defined by the unique subdomain for the URL—for example, www.mysite.com and extra.mysite.com are two different hosts. This limit is calculated across all organizations that access the same host. If this limit is exceeded, a CalloutException is thrown.

So If 20 other users across all salesforce organizations will access the same host at same point in time (Probably calculated in milliseconds), you will hit this salesforce limit.


This limit is there in API 39 but has vanished from the API 40 docs. (and the crowd rejoiced)

  • is this documented somewhere?
    – glls
    Aug 14 '17 at 15:06
  • Is it documented as going away? I did look thru the summery 17 release notes and didn't see any mention of it. Could be somewhere else, though. I just noticed that it wasn't in the limits page any more unless you set the API version back to 39. Aug 14 '17 at 19:05

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