Arvados » Arvados Workbench 2

GET requests embed the filters in the "query" portion of the URL. However, when filters get very large (such as requesting a large number of specific uuids, such as when requesting details about child containers) the URL can exceed the server's limit on URL length, causing the request to fail.

To work around this, the API server support queries using POST. The query goes in the body of the request (application/x-www-form-urlencoded), with an added query parameter "_method=GET" so it will be processed as a GET request. This is documented here:

https://doc.arvados.org/api/requests.html

In addition, queries on large numbers of uuids can be broken up into batches (this may also provide a better user experience by showing loading progress sooner).