LWLock:SInvalWrite

Waiting to add a message to the shared catalog invalidation queue.

What is the Shared Invalidation Queue?

Every PostgreSQL session (backend) keeps its own local cache of the system catalogs (metadata about tables, indexes, and columns) to avoid querying the disk for every SQL statement. However, when one session changes a table's structure (e.g., ALTER TABLE), the other sessions need to know that their local caches are now "stale."