The MDEX Engine always runs in multithreaded mode with the default number of threads set to 1. Multithreaded mode cannot be disabled.

The MDEX Engine always starts with a pool of threads that you can control with the --threads flag. These threads include query processing and partial update processing threads and additional threads that support query and update processing.

Each thread acts like an independent MDEX Engine, processing client requests one at a time and performing other tasks that support these requests, such as sorting and background index merging. It is important that the threads share data, memory, and the server network port.

Thus, a multithreaded MDEX Engine with n threads appears to be a single MDEX Engine process that can work on n queries at a time. Each of the independent threads can run on independent CPUs (or cores), enabling a single multithreaded MDEX Engine to make use of multi-processor hardware.

Multiple threads can also share a processor, especially a multi-core processor, allowing an MDEX Engine running on a single-processor host to remain responsive as long-running queries are handled.