The headline in 19 is REPACK, a single command that folds in what VACUUM FULL and CLUSTER used to do separately — and unlike either of them it has a CONCURRENTLY mode that doesn't take an exclusive lock. Parallel autovacuum finally lands, and a new WAIT command gives you read-your-writes consistency against a standby. One feature didn't survive the beta: SQL/PGQ, the property-graph query support, was pulled. A few defaults change under you. standard_conforming_strings is now always on and escape_string_warning is gone, so backslash-escaped string literals behave differently than on an old server. max_locks_per_transaction doubles from 64 to 128. RC1 landed October 15; a second candidate is due November 12 alongside the quarterly minor, and GA should follow on November 19 if nothing slips. Test your upgrade now — the whole point of an RC is that it's close to what you'll run.