Occasional tablespace.sql failures in check-world -jnn

Hi,

For fairly obvious reasons I like to run check-world in parallel [1]. In
the last few months I've occasionally seen failures during that that I
cannot recall seeing before.

--- /home/andres/build/postgres/13-assert/vpath/src/test/regress/expected/tablespace.out 2020-12-07 18:41:23.079235588 -0800
+++ /home/andres/build/postgres/13-assert/vpath/src/test/regress/results/tablespace.out 2020-12-07 18:42:01.892632468 -0800
@@ -209,496 +209,344 @@
ERROR: cannot specify default tablespace for partitioned relations
CREATE TABLE testschema.dflt (a int PRIMARY KEY USING INDEX TABLESPACE regress_tblspace) PARTITION BY LIST (a);
ERROR: cannot specify default tablespace for partitioned relations
-- but these work:
CREATE TABLE testschema.dflt (a int PRIMARY KEY USING INDEX TABLESPACE regress_tblspace) PARTITION BY LIST (a) TABLESPACE regress_tblspace;
SET default_tablespace TO '';
CREATE TABLE testschema.dflt2 (a int PRIMARY KEY) PARTITION BY LIST (a);
DROP TABLE testschema.dflt, testschema.dflt2;
-- check that default_tablespace doesn't affect ALTER TABLE index rebuilds
CREATE TABLE testschema.test_default_tab(id bigint) TABLESPACE regress_tblspace;
+ERROR: could not create directory "pg_tblspc/16387/PG_13_202007201/16384": No such file or directory
INSERT INTO testschema.test_default_tab VALUES (1);

(many failures follow)

I suspect this is related to the pg_upgrade test and the main regression
test running at the same time. We have the following in src/test/regress/GNUMakefile

# Tablespace setup

.PHONY: tablespace-setup
tablespace-setup:
echo $(realpath ./testtablespace) >> /tmp/tablespace.log
rm -rf ./testtablespace
mkdir ./testtablespace
...

which pg_upgrade triggers. Even though it, as far as I can tell, never
actually ends up putting any data in it:

# Send installcheck outputs to a private directory. This avoids conflict when
# check-world runs pg_upgrade check concurrently with src/test/regress check.
# To retrieve interesting files after a run, use pattern tmp_check/*/*.diffs.
outputdir="$temp_root/regress"
EXTRA_REGRESS_OPTS="$EXTRA_REGRESS_OPTS --outputdir=$outputdir"
export EXTRA_REGRESS_OPTS
mkdir "$outputdir"
mkdir "$outputdir"/testtablespace

It's not clear to me why we have this logic in the makefile at all?
Somebody taught pg_regress to do so, but only on windows... See
convert_sourcefiles_in().

The other thing that confuses me is why I started getting that error in
*multiple* branches recently, even though I have used the parallel
check-world for ages.

Greetings,

Andres Freund

[1]: make -Otarget -j20 -s check-world && echo success || echo failed