EWS: Throttling

[benbucksch]

Reproduction

• Set up ben@beonex.onm account
• Click on a few emails in Inbox

Actual result

• Error console shows:

  Account.ts:32 Error: The server cannot service this request right now. Try again later., This operation exceeds the throttling budget for policy part 'ConcurrentSyncCalls', policy value '5',  Budget type: 'Ews'.  Suggested backoff time 5000 ms.
  at EWSAccount.checkResponse (EWSAccount.ts:176:13)
  at EWSAccount.callEWS (EWSAccount.ts:206:19)
  at async EWSFolder.updateChangedMessages (EWSFolder.ts:86:18)
  at async EWSAccount.processNotification (EWSAccount.ts:361:11)
  at async EWSAccount.ts:293:9

Expected result

• We honor policies that the server pro-actively tells us
• When we receive an error message like this, we parse it, and honor the values given in the error message

Cause

We did too many things in parallel:

• Download Sent folder after setup
• Downloading Inbox
• Marking messages as read
• Folder notifications cause a sync

Solution

Throttle:

• Number of concurrent calls
• Number of calls per second

Parse errors:

• Error types
• Numeric values in the error data structure
• Numeric values in the error message

[benbucksch]

Throttle:

• Number of concurrent calls
• Number of calls per second

Parse errors:

• Error types
• Numeric values in the error data structure
• Numeric values in the error message

[NeilRashbrook]

How many calls per second do you want? (Exchange doesn't have a specific limit or policy for this.)

[benbucksch]

Let's start with 5 per second and dial down as needed?

[NeilRashbrook]

Five per second? We're defaulting to 20 at once...

[benbucksch]

Then let's make a limit of 50 calls per second by default.