In order to execute the DDL statement for an online index rebuild, all active blocking transactions running on a particular table must be completed. When the online index rebuild executes, it blocks all new transactions that are ready to start execution on this table. Although the duration of the lock for online index rebuild is very short, waiting for all open transactions on a given table to complete and blocking the new transactions to start, might significantly affect the throughput, causing a workload slow down or timeout, and significantly limit access to the underlying table. The WAIT_AT_LOW_PRIORITY option allows DBA's to manage the S-lock and Sch-M locks required for online index rebuilds and allows them to select one of 3 options. In all 3 cases, if during the wait time ( (MAX_DURATION = n [minutes]) ), there are no blocking activities, the online index rebuild is executed immediately without waiting and the DDL statement is completed.