Re: [PERFORM] Why is n_distinct always -1 for range types?
On 09/19/2013 01:47 PM, Josh Berkus wrote: Test: 1. create a table with a range type column. 2. insert 1000 identical values into that column. 3. analyze 4. n-distinct will still be listed as -1 (unique) for the column. Why? Anyone? -- Josh Berkus PostgreSQL Experts Inc. http://pgexperts.com -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Why is n_distinct always -1 for range types?
On Thu, Sep 19, 2013 at 1:47 PM, Josh Berkus j...@agliodbs.com wrote: 4. n-distinct will still be listed as -1 (unique) for the column. Why? Because of this: https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/rangetypes_typanalyze.c#L205 We only collect and use histograms of lower and upper bounds for range types, and the fraction of empty ranges. -- Regards, Peter Geoghegan -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
