arangodb/Documentation/DocuBlocks/indexThreads.md

@brief number of background threads for parallel index creation --database.index-threads

Specifies the number of background threads for index creation. When a collection contains extra indexes other than the primary index, these other indexes can be built by multiple threads in parallel. The index threads are shared among multiple collections and databases. Specifying a value of 0 will turn off parallel building, meaning that indexes for each collection are built sequentially by the thread that opened the collection. If the number of index threads is greater than 1, it will also be used to built the edge index of a collection in parallel (this also requires the edge index in the collection to be split into multiple buckets).