Re: [HACKERS] Orphaned files in base/[oid]

Hi,

On 2017-08-14 14:12:22 +0200, Chris Travers wrote:
> 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.
>
> So my question is if there is a way we can safely clean these up on server
> restart?  If not does it make sense to try to create a utility that can
> connect to PostgreSQL, seek out valid files, and delete the rest?

I think the fix here is to call RemovePgTempFiles() during
crash-restarts, instead of just full starts. The previously stated need
to be able to inspect temp files after a crash can be less impactfully
fulfilled with restart_after_crash = false.

Greetings,

Andres Freund