If query uses a range-restricted predicate, the query processor can use the min and max values to rapidly skip over large numbers of blocks during table scans The min and max values for each block are stored as part of the metadata. Redshift stores columnar data in 1 MB disk blocks.Only one sort key per table can be defined, but it can be composed with one or more columns.Sorting enables efficient handling of range-restricted predicates.Sort keys define the order in which the data will be stored.Amazon Redshift applies AUTO distribution, be default.apply ALL distribution for a small table and as it grows changes it to Even distribution Redshift assigns an optimal distribution style based on the size of the table data for e.g.Small dimension tables DO NOT benefit significantly from ALL distribution, because the cost of redistribution is low.
ideal for for relatively slow moving tables, tables that are not updated frequently or extensively.
ensures that every row is collocated for every join that the table participates in. whole table is replicated in every compute node. when there is not a clear choice between KEY and ALL distribution. when the table does not participate in joins. distributes the rows across the slices in a round-robin fashion, regardless of the values in any particular column. acts as a JOIN column – for tables related with dimensions tables (star-schema), it is better to choose as DISTKEY the field that acts as the JOIN field with the larger dimension table, so that matching values from the common columns are physically stored together, reducing the amount of data that needs to be broadcasted through the network. Is uniformly distributed – Otherwise skew data will cause unbalances in the volume of data that will be stored in each compute node leading to undesired situations where some slices will process bigger amounts of data than others and causing bottlenecks. As a rule of thumb, choose a column that:. A single column acts as distribution key (DISTKEY) and helps place matching values on the same node slice. Redshift supports four distribution styles AUTO, EVEN, KEY, or ALL. Table distribution style determines how data is distributed across compute nodes and helps minimize the impact of the redistribution step by locating the data where it needs to be before the query is executed. AWS Redshift Advanced topics cover Distribution Styles for table, Workload Management etc.
0 kommentar(er)
