Improve handling of empty query results in BackgroundPsql::query()

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
index c7a3d3e920d45c1a219f0cd22905c163e7bab5c7..2216918b253c68051190de699c222e1844c148c8 100644 (file)
--- a/src/test/perl/PostgreSQL/Test/BackgroundPsql.pm
+++ b/src/test/perl/PostgreSQL/Test/BackgroundPsql.pm
@@ -236,8 +236,10 @@ 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
index 6d1c71179642178b3550013b2920a15d75f16e53..3735086aee4c06b861fd71cd8404aa2be8048526 100644 (file)
--- a/src/test/recovery/t/037_invalid_database.pl
+++ b/src/test/recovery/t/037_invalid_database.pl
@@ -96,13 +96,12 @@ my $bgpsql = $node->background_psql('postgres', on_error_stop => 0);
 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.
 $bgpsql->query_until(qr//, "DROP DATABASE regression_invalid_interrupt;\n");
@@ -135,11 +134,8 @@ is($node->psql('regression_invalid_interrupt', ''),
 
 # 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();