The MDEX Engine places a cap on the number of threads available for partial updates and admin operations (such as admin?op=update, admin?op=ping, and generation merging).

This cap is set by the formula (N+1)/2, where "N" is the number of threads made available for the MDEX Engine at startup time, using the --threads option of the dgraph command. When this cap is reached, admin operations can no longer execute.

A smaller number of threads, as specified by the -- threads option, makes it more likely that running partial updates will hinder or block other admin operations by using all the (N + 1) / 2 threads allowed for admin operations

Recommended practice is to have at least 8 cores available on a MDEX machine that will run partial updates. This will help prevent partial updates and other administrative operations from reaching their cap. It will also help ensure that enough threads are available for other operations run by the MDEX Engine.