You'd generally add an index to your logs in Clickhouse to do searching (via ngram or token bloom filters typically: https://clickhouse.com/docs/en/optimize/skipping-indexes#blo...). There's other ways of indexing as well but that's generally the best for full text search. We use token bloom filter indexes today and find them quite effective (it can skip whole chunks of logs due to the bloom filter being able to say that a word did not appear in the chunk of logs).

Indeed Loki is incredibly slow - Clickhouse is deployed for logging at scale (ex. trip.com is running a 50pb logging solution that allowed them to 4x their old ES cluster volume while also running queries 4-30x faster)