Presto supports statistics based optimizations for queries. For a query to take advantage of these optimizations, Presto must have statistical information for the tables in that query.
Table statistics are provided to the query planner by connectors.
The following statistics are available in Presto:
For a table:
row count: the total number of rows in the table
For each column in a table:
data size: the size of the data that needs to be read
nulls fraction: the fraction of null values
distinct value count: the number of distinct values
low value: the smallest value in the column
high value: the largest value in the column
The set of statistics available for a particular query depends on the connector being used and can also vary by table. For example, the Hive connector does not currently provide statistics on data size.