Just want to know what is the Limits and Boundaries of SharePoint Online for Bulk operations. Is there any authentic document I can refer? I am trying to insert 20,000 items with 5 text fields in a batch of 100. sometimes it throws Error "The Operation has timed out" I am using jquery + rest api to perform this bulk operation
This does not give you the limits but maybe a solution for your problem.
The bulk limits for SharePoint 2013 is 100 items per operation so i guess it is around that number in Online aswell. SharePoint 2013 Software boundaries
But to resolve your problem try extending the RequestTimeout for your context.
But as you are using jQuery and the rest api try setting the timeout property on the ajax call. jQuery ajax documentation
Are you doing real bulk requests, or do you make a request per item?
If it is the later, try to schedule your requests and give SP some time. I don't think there are official hard numbers, since there are a lot of relevant factors that are not limited to the service for a timeout to occur.
Had the same problem with general CRUD operations. I would suggest to leave some time between any two requests and don't bulk transfer anything.
(real bulk (batch) requests are possible and shouldn't have this problem. They are available in newer SP installations, but I don't know about their limits. Didn't find a lot of documentation, although that might have been improved.)