PostgreSQL 18 Upgrade Guide: Async I/O, Skip Scan, UUIDv7, and the Checks That Matter
A practical PostgreSQL 18 upgrade guide covering async I/O, skip scan indexes, uuidv7, pg_upgrade statistics, checksums, MD5 password deprecation, and rollout testing.
In This Article
Why PostgreSQL 18 Is Worth a Careful Look
PostgreSQL 18 is a high-interest database release because it touches performance, indexing, UUID generation, authentication, migration behavior, and operational defaults. The practical search terms are PostgreSQL 18 upgrade guide, PostgreSQL 18 async I/O, Postgres skip scan, uuidv7 PostgreSQL, pg_upgrade statistics, and MD5 password deprecation.
The headline features are useful, but the upgrade should still start with boring checks: extensions, backups, restore tests, query plans, application drivers, connection pools, authentication, and rollback.
Treat PostgreSQL 18 as an infrastructure change, not a package bump. A database upgrade can succeed technically and still surprise you through changed plans, changed defaults, or old scripts.
Async I/O Helps Some Workloads More Than Others
PostgreSQL 18 adds an asynchronous I/O subsystem that can queue multiple read requests. The official release notes call out sequential scans, bitmap heap scans, vacuum, and related operations as places that may benefit.
That does not mean every query gets faster. Index-heavy OLTP queries, network-limited apps, slow application code, and lock contention may see little change. Benchmark the real workload: reporting queries, batch jobs, vacuum behavior, read-heavy endpoints, and any table scans that currently dominate latency.
Record plans and timings before the upgrade. Then compare the same queries on PostgreSQL 18 with realistic data, cold-cache and warm-cache runs, and production-like storage.
Skip Scan Can Make Existing Indexes More Useful
Skip scan support lets PostgreSQL use some multicolumn B-tree indexes in more cases, including when the first indexed column is not restricted but later columns are useful for the query.
This is not a reason to stop designing indexes carefully. It is a reason to re-check slow queries after the upgrade before adding duplicate indexes. Some queries that previously needed a new single-column index may become acceptable with an existing multicolumn index.
Use EXPLAIN before and after. If the plan changes, verify latency, rows read, buffer usage, and whether the new plan stays stable across realistic parameter values.
UUIDv7 Is Practical for New Tables
PostgreSQL 18 includes uuidv7(), which generates timestamp-ordered UUIDs. That matters because random UUIDs can scatter inserts across an index, while time-ordered identifiers can be friendlier for write patterns and sorting by creation time.
Do not rewrite every existing primary key just because UUIDv7 exists. Use it for new tables, event records, public identifiers, and systems that already prefer UUIDs but want better index locality.
If you migrate an existing ID strategy, test application assumptions, replication, API contracts, analytics exports, and any code that sorts by ID as a proxy for time.
Upgrade Checks That Matter in Production
PostgreSQL 18 changes several operational details worth checking. pg_upgrade can retain optimizer statistics, new clusters enable data checksums by default through initdb, MD5 password authentication is deprecated, and some full-text search or pg_trgm cases may need reindexing depending on collation behavior.
Make a short upgrade runbook: take a backup, restore it in staging, list extensions, run application tests, compare critical query plans, test connection pools, verify authentication, run migrations, check jobs, and rehearse rollback.
After production cutover, watch error logs, query latency, autovacuum, replication lag, locks, disk growth, and the slowest user-facing endpoints. The best PostgreSQL 18 upgrade is the one that users barely notice.