backport: Improve handling of empty query results in BackgroundPsql

anarazel · anarazel · commit 3c562b58c20e · 2025-02-19T09:52:32.000-05:00
This is a backport of 70291a3. 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. 70291a3 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
diff --git a/src/test/perl/PostgreSQL/Test/BackgroundPsql.pm b/src/test/perl/PostgreSQL/Test/BackgroundPsql.pm
@@ -222,8 +222,10 @@ sub query
 	die "psql query timed out" if $self->{timeout}->is_expired;
 	$output = $self->{stdout};
 
-	# remove banner again, our caller doesn't care
-	$output =~ s/\n$banner\n$//s;
+	# Remove banner again, our caller doesn't care.  The first newline is
+	# optional, as there would not be one if consuming an empty query
+	# result.
+	$output =~ s/\n?$banner\n$//s;
 
 	# clear out output for the next query
 	$self->{stdout} = '';
diff --git a/src/test/recovery/t/037_invalid_database.pl b/src/test/recovery/t/037_invalid_database.pl
@@ -92,13 +92,12 @@
 my $pid = $bgpsql->query('SELECT pg_backend_pid()');
 
 # create the database, prevent drop database via lock held by a 2PC transaction
-ok( $bgpsql->query_safe(
-		qq(
+$bgpsql->query_safe(
+	qq(
   CREATE DATABASE regression_invalid_interrupt;
   BEGIN;
   LOCK pg_tablespace;
-  PREPARE TRANSACTION 'lock_tblspc';)),
-	"blocked DROP DATABASE completion");
+  PREPARE TRANSACTION 'lock_tblspc';));
 
 # Try to drop. This will wait due to the still held lock.
 $bgpsql->query_until(qr//, "DROP DATABASE regression_invalid_interrupt;\n");
@@ -131,11 +130,8 @@
 
 # To properly drop the database, we need to release the lock previously preventing
 # doing so.
-ok($bgpsql->query_safe(qq(ROLLBACK PREPARED 'lock_tblspc')),
-	"unblock DROP DATABASE");
-
-ok($bgpsql->query(qq(DROP DATABASE regression_invalid_interrupt)),
-	"DROP DATABASE invalid_interrupt");
+$bgpsql->query_safe(qq(ROLLBACK PREPARED 'lock_tblspc'));
+$bgpsql->query_safe(qq(DROP DATABASE regression_invalid_interrupt));
 
 $bgpsql->quit();
 
