phacility/phabricator · critical · Exception

Multiple configured databases have the same internal key, "%

Error message

Multiple configured databases have the same internal key, "%s". You may have listed a database multiple times.

What it means

Every configured database ref gets an internal key (derived from host:port). While building the ref map, the parser throws if two refs produce the same key, which almost always means the same server is listed more than once in cluster.databases.

Source

Thrown at src/infrastructure/cluster/PhabricatorDatabaseRefParser.php:150

        }

        $ref->setApplicationMap($application_map);
      }
    } else {
      // If we only have one master, make it the default.
      foreach ($refs as $ref) {
        if ($ref->getIsMaster()) {
          $ref->setIsDefaultPartition(true);
        }
      }
    }

    $ref_map = array();
    $master_keys = array();
    foreach ($refs as $ref) {
      $ref_key = $ref->getRefKey();
      if (isset($ref_map[$ref_key])) {
        throw new Exception(
          pht(
            'Multiple configured databases have the same internal '.
            'key, "%s". You may have listed a database multiple times.',
            $ref_key));
      } else {
        $ref_map[$ref_key] = $ref;
        if ($ref->getIsMaster()) {
          $master_keys[] = $ref_key;
        }
      }
    }

    foreach ($refs as $key => $ref) {
      if ($ref->getIsMaster()) {
        continue;
      }

      $server = $config[$key];

View on GitHub (pinned to 5720a38cfe)

Solutions

Give every entry a unique host:port combination; for the intended replica, point it at the replica's real host.
Remove accidentally duplicated blocks from cluster.databases.
Run 'bin/config get cluster.databases' and eyeball for repeated addresses before reloading.

Example fix

// before
[
  ["master" => true, "host" => "db1.internal", "port" => 3306],
  ["master" => false, "host" => "db1.internal", "port" => 3306] // duplicate key
]

// after
[
  ["master" => true, "host" => "db1.internal", "port" => 3306],
  ["master" => false, "host" => "db1-replica.internal", "port" => 3306]
]

Defensive patterns

Strategy: validation

Validate before calling

// Detect duplicate host:port refs before deploy
$keys = array();
foreach ($cluster_database_config as $server) {
  $key = idx($server, 'host').':'.idx($server, 'port', 3306);
  if (isset($keys[$key])) {
    // reject: same internal key listed twice
  }
  $keys[$key] = true;
}

Prevention

When adding a replica, change the 'host' (not just 'master' => false) so the ref key stays unique.
Search cluster.databases for repeated addresses after any copy-paste edit.
Prefer generating database cluster config from a template with per-node variables.

When it happens

Trigger: Two entries in cluster.databases with the same host and port (e.g. a master block and a copied block meant to be a replica where the host was never changed); the same server listed under different roles.

Common situations: Setting up a replica by duplicating the master config and forgetting to change 'host'; adding a second application database on the same MySQL instance with an identical address; config merges producing a duplicated block.

Related errors

AI-assisted analysis of phacility/phabricator@5720a38cfe (2026-08-21). Data as JSON: /api/errors/f6d1ffe313403a77. Report an issue: GitHub.