Physical Database Design

152 CHAPTER 8 Multidimensional Clustering

– Using MDC data is never placed in the wrong cell.

• Scans on any dimension index provide clustered data access.

– Each block ID identifies a storage block guaranteed to contain data having

that dimension value.

• Dimensions/slices can be accessed independently using their block indexes.

– One block index does not impact the cluster factor of another block index.

• Block index scans can be combined (ANDed, ORed).

– The resulting list of blocks also provides clustered data access.

• Access to the clustered data is much faster.

– More efficient scan using a block ID to access blocks versus multiple RIDs

for each row.

• Enabled MDC-specific ‘block lookahead prefetching’.

– Read ahead in the index and prefetch the ...