A special UNDO log algorithm combining the advantages of update in place strategies with the shadow page concept is introduced. It is to support applications demanding high rates of possibly long update transactions as well as fast UNDO recovery. By doubling the disk space for the database, UNDO loggng can be performed with a minimum of additional I/O operations. Thus, we gain a performance comparable to systems without any UNDO loggg. Since in this algorithm one logical slot consists of two physical blocks, the name TWIST (twin slot) algorithm is proposed.