Expect to come across this popular DB2 tricky interview questions First, MDC enables a table to be physically clustered on more than one key, or dimension, simultaneously. As a result query performance is improved where there is a clustering of one or more specified dimensions of a table. Consequently not only will these queries access only those pages having records with the correct dimension values, but these qualifying pages will also be grouped into blocks, or extents. Second, although a table with a clustering index can become unclustered over time, in most cases an MDC table is able to maintain and guarantee its clustering overall dimensions automatically and continuously. Third, in MDC the clustering indexes are block-based. These indexes are much smaller than regular record-based indexes, hence they take up much less disk space and are faster to scan.