An Overview of Index Prefetching
October 20–23
Level: Intermediate
PostgreSQL 18 brought asynchronous I/O to most scan types, letting Postgres read ahead and hide storage latency instead of stalling on every page read. But support for "plain" index scans was deferred. Such support requires a fundamental rethink of how the scan orders work internally, making it a large and complicated project in its own right.
Work now targeting PostgreSQL 20 will add support for prefetching during index scans. This talk (giving by one of the authors of the index prefetching patch set) looks at what that means for users: which kinds of queries are faster, and by how much.
