Recoll is free/open source (GPL) that can index PDFs and search them very quickly. It uses Xapian under the hood. I have over 165,000 documents indexed on an old laptop running Linux and can query them all in a split second. Source: 8 months ago

+ xapian which has been around a while, and while gpl licensed, is quite capable https://xapian.org/. - Source: Hacker News / over 1 year ago

Tangentially related if you need search without the clustering and high availability story of elastic search and friends I highly recommend Xapian. Its like the SQLite of search. Single library that provides the basic set of features you would expect in a quality search experience: facets, ranked search, boolean operators, stemming etc etc. https://xapian.org/. - Source: Hacker News / over 1 year ago

For fast searching, it usually requires indexing the files in question. There are a number of text-file indexing solutions, many of which use xapian, sphinx, or lucene/solr under the hood. Based on conditions (watching files/directories, cron jobs, new-mail triggers, etc), they'll add/remove files to the index, and you can then use a corresponding command to compose queries across that data. If it's indexed, it... Source: over 2 years ago

There is also xapian/recoll https://xapian.org/ which works great for "desktop" search. - Source: Hacker News / over 2 years ago

If you are looking for something more lightweight to start out with, I'd suggest a look at logwatch. Source: over 2 years ago

Logwatch can be used, as well: https://sourceforge.net/projects/logwatch/ (default behavior is digest notifications, though). Source: almost 3 years ago