Ask HN: Is there a search engine that performs “Exact Search”?
[a crude speculative outline]<p>No. Because to a first approximation, it is not possible to make it work <i>all the time</i> in practice.<p>Results returned are best effort. Best effort is largely limited by latency.<p>At the scale of the entire web, parts of the index will be absolutely inaccessible due to partitioning and practically inaccessible because they are sitting on disk (or simply don’t exist because they wouldn’t fit into memory) or are so far away that they can’t reliably be returned within the limits of acceptable latency — e.g. on a server in Japan for a London query (and anyway how likely is relevance of Japanese results?).<p>I mean maybe there are results for the “site” qualifier in memory on the server your query hits and maybe their aren’t. Either way, Google’s going to return results in 250ms if that’s the performance target. Either way Google’s not going to spin for twenty minutes or seconds it would take to crawl the site, process the results, and build the inverted index.<p>Everything is engineered. The engineering is guided by statistics. But so is performance. Sometimes better information is close by in hot memory. Sometimes it isn’t. Sometimes bandwidth is saturated. Sometimes your cell service is slow.<p>That’s probably why HN uses Algolia even though it costs money.