[HACKERS] Orphaned files in base/[oid]

I am trying to track down a problem we are seeing that looks very similar to bug #12050, and would certainly consider trying to contribute a fix if we agree on one.  (I am not sure we can, so absent that, the next question is whether it makes sense to create a utility to fix the problem when it comes up so that a dump/restore is not needed).

The system:

PostgreSQL 9.6.3

Gentoo Linux.

Problem:

The system this came up on is PostgreSQL 9.6.3 and has had repeated trouble with disk space.  Querying pg_database_size, as well as du on the subdirectory of base/ show total usage to be around 3.8TB.  Summing up the size of the relations in pg_class though shows around 2.1TB. 

Initial troubleshooting found around 150 GB of space in pg_temp which had never been cleared and was at least several days old.  Restarting the server cleared these up.

Poking around the base/[oid] directory, I found a large number of files which did not correspond with a pg_class entry.  One of the apparent relations was nearly 1TB in size.

What I think happened:

I think various pg_temp/* and orphaned relation files (In base/[oid]) were created when PostgreSQL crashed due to running out of space in various operations including creating materialised views.
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