The graph tooltip shows the data for a single timestamp. There can be hundreds of data points for the timestamp, but the tooltip is limited to showing the top 20. In this case, the code is quite inefficient because it both sorts and then processes all data points before throwing away all but the top 20.
checked with 4.9.0-0.nightly-2021-08-29-010334, the tooltip shows the top 20 results, and the it takes less time to get the result
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (Moderate: OpenShift Container Platform 4.9.0 bug fix and security update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2021:3759