SQList uses SharePoint web services to continuously poll the lists for changes to be replicated to the SQL database. This constant polling generates continuous requests to the SharePoint site, especially if you run SQList as a service rather than as a scheduled job.
Despite these requests are very quick and take very little resources, you must be aware of them when replicating sites from SharePoint Online.
SharePoint Online uses throttling to maintain optimal performance and reliability of the SharePoint Online service. Throttling limits the number of user actions or concurrent calls (by script or code) to prevent overuse of resources.
For more information about throttling, please refer to this article:
If you notice any of these errors in the SQList event log, your site is probably being throttled:
- "503 Server unavailable message"
- "429 Too many requests"
From SQList 5.4 onward, the default delay is 200 milliseconds for all sites, which should prevent any sites from being throttled.
If your site does get throttled, we recommend increasing the delay duration to 500 milliseconds initially, then to 1,000 if you still have the issue (although that is very unlikely to happen).
To minimise throttling in SharePoint Online, we introduced an additional site definition configuration setting in SQList 5.4. In the site definition details, there is a new setting named "Throttling control delays"; you can use this setting to define the duration (in milliseconds) of the delay SQList will add between requests to that particular site.
Note that while this setting is particularly aimed to SharePoint Online sites, it can be useful for on-prem sites to reduce the amount of pressure put on the SharePoint WFEs.