As your database grows in size, you'll need to paginate results returned. Pagination improves performance by returning a subset of results that match a query at a time, called a page.
By default, list operations return 25 items per page, which can be changed using the Query.limit(25) operator. There is no hard limit on the number of items you can request. However, beware that large pages can degrade performance.
Offset pagination
Offset pagination works by dividing documents into M pages containing N documents. Every page is retrieved by skipping offset = M * (N - 1) items and reading the following M pages.
Using Query.limit() and Query.offset() you can achieve offset pagination. With Query.limit() you can define how many documents can be returned from one request. The Query.offset() is number of records you wish to skip before selecting records.
Drawbacks
While traditional offset pagination is familiar, it comes with some drawbacks. The request gets slower as the number of records increases because the database has to read up to the offset number M * (N - 1) of rows to know where it should start selecting data. If the data changes frequently, offset pagination will also produce missing and duplicate results.
Cursor pagination
The cursor is a unique identifier for a document that points to where the next page should start. After reading a page of documents, pass the last document's ID into the Query.cursorAfter(lastId) query method to get the next page of documents. Pass the first document's ID into the Query.cursorBefore(firstId) query method to retrieve the previous page.
When to use what?
Offset pagination should be used for collections that rarely change. Offset paginations allow you to create indicator of the current page number and total page number. For example, a list with up to 20 pages or static data like a list of countries or currencies. Using offset pagination on large collections and frequently updated collections may result in slow performance and missing and duplicate results.
Cursor pagination should be used for frequently updated collections. It is best suited for lazy-loaded pages with infinite scrolling. For example, a feed, comment section, chat history, or high volume datasets.