PostgreSQL: Disk space not released after TRUNCATE

Question

I haveTRUNCATEd a huge (~120Gb) table called files:

TRUNCATE files;
VACUUM FULL files;

The table size is 0, but no disk space was released. Any ideas how to reclaim my lost disk space?

UPDATE: The disk space was released after ~12 hours, without any action on my side. I use Ubuntu 8.04 server.

Answer 1

According to comments in the source, truncate creates a new, empty storage file, and deletes the old storage file at commit time. (Docs suggest "storage file" is just a file as far as the OS is concerned, but I might be misunderstanding the terminology.)

Create a new empty storage file for the relation, and assign it as the relfilenode value. The old storage file is scheduled for deletion at commit.

Since it seems to be deleting a file, I can imagine some cases in which the underlying operating system might not immediately free that space. I imagine that in some cases the storage file might end up in the Recycling Bin under Windows, for example. But in my case, truncating a table under PostgreSQL 9.something immediately increased the freespace under Windows.

Truncation is also recorded in the WAL log. I don't know how much effect that might have.