PostgreSQL stores the data in a different way (each object gets a different file, or several files), so extending the size of tablespace files is not a big issu

PostgreSQL stores the data in a different way (each object gets a different file, or several files), so extending the size of tablespace files is not a big issue and dropping objects is as simple as deleting the file. The LRU is basically the shared_buffers, and that's where most of the 9.2 improvements were (more or less).