backport: Improve handling of empty query results in BackgroundPsql
This is a backport of 70291a3c66e. Originally it was only applied to master,
but I (Andres) am planning to fix a few bugs in BackgroundPsql that are harder
to fix in the backbranches with the old behavior. It's also generally good for
test infrastructure to behave similarly across branches, to avoid pain during
backpatching. 70291a3c66e changes the behavior in some cases, but after
discussing it, we are ok with that, it seems unlikely that there are
out-of-core tests relying on the prior behavior.
Discussion: https://postgr.es/m/ilcctzb5ju2gulvnadjmhgatnkxsdpac652byb2u3d3wqziyvx@fbuqcglker46
Michael's original commit message:
A newline is not added at the end of an empty query result, causing the
banner of the hardcoded \echo to not be discarded. This would reflect
on scripts that expect an empty result by showing the "QUERY_SEPARATOR"
in the output returned back to the caller, which was confusing.
This commit changes BackgroundPsql::query() so as empty results are able
to work correctly, making the first newline before the banner optional,
bringing more flexibility.
Note that this change affects 037_invalid_database.pl, where three
queries generated an empty result, with the script relying on the data
from the hardcoded banner to exist in the expected output. These
queries are changed to use query_safe(), leading to a simpler script.
The author has also proposed a test in a different patch where empty
results would exist when using BackgroundPsql.
Author: Jacob Champion
Reviewed-by: Andrew Dunstan, Michael Paquier
Discussion: https://postgr.es/m/CAOYmi+=60deN20WDyCoHCiecgivJxr=98s7s7-C8SkXwrCfHXg@mail.gmail.com
Branch
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REL_17_STABLE
Details
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https://git.postgresql.org/pg/commitdiff/31a242e90c8857c0e79e76e324a84f935d3cfedf
Modified Files
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src/test/perl/PostgreSQL/Test/BackgroundPsql.pm | 6 ++++--
src/test/recovery/t/037_invalid_database.pl | 14 +++++---------
2 files changed, 9 insertions(+), 11 deletions(-)
