On-line transaction systems with high performance demands need a variety of concurrency control methods used for synchronizing data access of even a single transaction. Simple protocols based on strict two-phase locking would not meet their performance goals. This is particularly true for usage patterns of special data elements known as "hot spots". In this paper, we review various solutions for concurrency control on aggregate data, where the operations to be synchronized commute-at least for certain value ranges. In particular, the escrow mechanism introduced for centralized DBMS is discussed and extended. Our investigations focus on the escrow mechanism for a data sharing environment where transactions running on multiple, independent processors must be efficiently synchronized without sacrificing their serializability. First of all, we propose the use of global escrow services, which may be called asynchronously. Such an optimistic attitude seems to be appropriate, since rejections of escrow operations typically are rare events. The performance of the proposed scheme may be further improved be refining it to a hierarchical escrow scheme with a global escrow and distributed local escrows. Both approaches may be favorably integrated either in a centralized locking scheme or in a primary copy authority scheme for DB-sharing. © 1988.