Managing sort keys
Data sorting in Amazon Redshift is a concept regarding how data is physically sorted on the disk. Data sorting is determined by the sortkey property defined in the table. Amazon Redshift automatically creates in-memory metadata called zone maps. Zone maps contain the minimum and maximum values for each block. Zone maps automatically enable you to eliminate I/O from scanning blocks that do not contain data for queries. Sort keys make zone maps more efficient.
sortkey can be defined on one or more columns. The columns that are defined in the sort keys are based on your query pattern. Most frequently, filtered columns are good candidates for the sort key. The sort key column's order is defined from low to high cardinality. Sort keys enable range-restricted scans to prune blocks, eliminating I/O and hence optimizing query performance. Redshift Advisor provides recommendations on optimal sort keys, and automatic table optimization handles the sort key changes...
