Aleksey Tsalolikhin <atsaloli.tech at gmail.com> writes:
> Hi.  I dropped my large table from the replication set and then ran TRUNCATE
> against that table on the replica.  Disk usage according to "df" dropped from
> 98% to 96%.  I ran VACUUM FULL on that table but that did not help.
> I then shut down PostgreSQL and then started it again, and usage dropped
> to 6%.

Hah.  Almost certainly some file got unlinked, but some backend process
remained holding onto the file descriptor, so the space did not get
returned to the filesystem until that backend process terminated.

It's pretty likely that you could have done something less dramatic than
restarting PostgreSQL, but the restart was certainly an easy way to
flush out any such hanging FDs.

I'd anticipate that you'll find things work fine, now.

There's a mystery there, still, in terms of "what was that lingering
file descriptor???", but it's entirely possible that nothing similar
will ever recur.
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