罠 2-c: Sch-M ロックは ONLINE でも瞬間発生する

-- 現在のロック保持状況 (Sch-M / Sch-S を含む)
SELECT
    request_session_id      AS session_id,
    resource_type,
    resource_associated_entity_id,
    resource_lock_partition,
    request_mode,           -- Sch-M / Sch-S / S / X / IX 等
    request_type,
    request_status          -- GRANT / WAIT / CONVERT
FROM sys.dm_tran_locks
WHERE resource_type IN ('OBJECT', 'KEY', 'PAGE')
  AND request_mode IN ('Sch-M', 'Sch-S', 'X', 'IX')
ORDER BY request_session_id;