Qgrep Internals

In theory, the filesystem in-memory cache is supposed to make subsequent searches fast; on FIFA codebase, however, both file hierarchy and file contents was never fully in the filesystem cache, especially as you worked on the code (for example, switching to the browser to google something would likely evict large portions of the search data set). In later releases a few changes were made to address the slow compression performance:

As a result, it takes 6.5 seconds with hot file cache to rebuild UE4 search data from scratch and 1.2 seconds to update a single file in it; in the latter case most of the time is spent traversing file directory structure. To solve this problem, qgrep uses a special purpose ordered queue – the way it works is that the producers (search threads) submit items to that queue with an index indicating the original chunk index, and the single consumer that prints the output processes items in the order indicated by this index.

Source: zeux.io