I’be been a search engineer for >10 years and this is always the first book I recommend.
After I read it...
"...I knew NOTHING about search."
No book has ever knocked me off my pedestal so brutally and so thoroughly.
* Introduction to Information Retrieval, http://informationretrieval.org/
* Information Retrieval in Practice, http://www.search-engines-book.com/
* Entity-Oriented Search, https://eos-book.org/
Modern Information Retrieval is also a classic reference. Not openly available but some contents are (were?) available online. Their site seems to be down but the Internet Archive has a copy.
Additional resources here:
"Introduction to Information Retrieval" is a textbook which is available online https://nlp.stanford.edu/IR-book/ Here's a review: http://glinden.blogspot.com/2009/02/book-review-introduction...
Another textbook which IMHO is a bit lower level is "Information Retrieval: Implementing and Evaluating Search Engines". The book website is down for me right now, but you can find it on Amazon here: https://www.amazon.com/Information-Retrieval-Implementing-Ev...
Another commenter linked to "Relevant Search", which is great if you want to learn how to effectively use a search engine to improve relevance (as opposed to how to implement a search engine). It's old, but another book in that vein that was really helpful for me earlier in my career is Lucene in Action: https://www.amazon.com/Lucene-Action-Second-Covers-Apache/dp...
Old but good!
The book mentioned there is Lucene in Action.
And then this YouTube presentation by a Lucene/Elasticsearch committer will give you a nice overview of some related algorithms—
Also from that lecture series, the low level is always IO. One disk read tends to dwarf n^2 in-memory algorithms.
And IO is all about tuning caches and hardware for the specific structural relationships in the data, the way in which it is accessed, and the hardware everything runs on.
Also "taming text"