Written By: Guy Glantser 02/03/2018
This wait type indicates that parallel plans execute on the server. This wait type doesn’t necessarily means there is a problem. It only points to the existence of parallelism. In many systems, this wait type is very common, usually the top 1. The fact that it’s so common means there is a lot of parallelism. One of the reasons for having a lot of parallel plans is large scans. Scan operations are usually performed in parallel. By optimizing queries and/or adding the appropriate indexes, it is possible to reduce the number of scan operations and thus reduce parallelism in the system. In some cases a parallel plan does not execute efficiently, and reducing the max degree of parallelism might improve performance, but this is relatively rare. In most cases, if we reduce the max degree of parallelism, we will make things even worse, because now these large scans will have to be executed serially instead of in parallel. The right thing to do is to optimize the relevant queries in order to avoid the large scans in the first place.