20170918.ref.01.position.php

<?php

$table = new PhabricatorRepositoryRefPosition();
$conn = $table->establishConnection('w');
$key_name = 'key_position';

try {
  queryfx(
    $conn,
    'ALTER TABLE %T DROP KEY %T',
    $table->getTableName(),
    $key_name);
} catch (AphrontQueryException $ex) {
  // This key may or may not exist, depending on exactly when the install
  // ran previous migrations and adjustments. We're just dropping it if it
  // does exist.

  // We're doing this first (outside of the lock) because the MySQL
  // documentation says "if you ALTER TABLE a locked table, it may become
  // unlocked".
}

queryfx(
  $conn,
  'LOCK TABLES %T WRITE',
  $table->getTableName());

$seen = array();
foreach (new LiskMigrationIterator($table) as $position) {
  $cursor_id = $position->getCursorID();
  $hash = $position->getCommitIdentifier();

  // If this is the first copy of this row we've seen, mark it as seen and
  // move on.
  if (empty($seen[$cursor_id][$hash])) {
    $seen[$cursor_id][$hash] = true;
    continue;
  }

  // Otherwise, get rid of this row as it duplicates a row we saw previously.
  $position->delete();
}

queryfx(
  $conn,
  'ALTER TABLE %T ADD UNIQUE KEY %T (cursorID, commitIdentifier)',
  $table->getTableName(),
  $key_name);

queryfx(
  $conn,
  'UNLOCK TABLES');