1. A machine-implemented method, comprising: in response to a search query for metadata stored in one or more of a plurality of metadata stores, partitioning the search query into a plurality of search query segments; for each search query, allocating a system thread having a time slice with a predetermined time period; and performing searches corresponding to the plurality of search query segments, each search being performed independently within the one or more metadata stores within a corresponding time slice of a corresponding system thread in a round-robin manner, including storing a search state and a partial search result in a queue at the end of the time slice if the respective search has not been finished, such that the respective search can be carried on in a subsequent time slice.