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Message-ID: <0f515c6d-6032-4c5f-80ac-5c78faae9522@gmail.com>
Date: Sat, 8 Aug 2026 21:59:57 -0500
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To: pgsql-hackers@lists.postgresql.org
From: Bryan Green <dbryan.green@gmail.com>
Subject: [PATCH] Avoid uninitialized-value error in poll_query_until timeout
 diagnostic
Archived-At: 
 <https://www.postgresql.org/message-id/0f515c6d-6032-4c5f-80ac-5c78faae9522%40gmail.com>
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Greetings,

PostgreSQL::Test::Cluster::poll_query_until() accepts an undefined query 
for connection-only checks -- several recovery TAP tests call it that way:

     $node->poll_query_until('postgres', undef, '');


On timeout it builds a diag message that interpolates $query:

     diag qq(poll_query_until timed out executing this query:
     $query
     ...);

Cluster.pm runs under "use warnings FATAL => 'all'", so when $query is
undefined this does not warn, it dies with "Use of uninitialized value
$query in concatenation".  The result is that a timeout in a connection 
only poll fails with an uninitialized-value error instead of printing 
the timeout diagnostic the code is trying to produce, hiding the actual 
failure.

     $ perl -e 'use warnings FATAL => "all"; my $q; my $s = qq(q: $q);'
     Use of uninitialized value $q in concatenation (.) or string at -e 
line 1.

The fix uses a fallback string when the query is undefined:

     my $msg_query = $query // '(undef - connection attempt only)';

and interpolates $msg_query instead.  Test-only, one line.

--
Bryan Green
EDB: https://www.enterprisedb.com

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