On 5 August 2016 at 21:48, Tom Lane <t...@sss.pgh.pa.us> wrote: > OK, thanks. What shall we do about Andreas' request to back-patch this? > I'm personally willing to do it, but there is the old bugaboo of "maybe > it will destabilize a plan that someone is happy with". >
My inclination would be to back-patch it because arguably it's a bug-fix -- at the very least the old behaviour didn't match the docs for stadistinct: The number of distinct nonnull data values in the column. A value greater than zero is the actual number of distinct values. A value less than zero is the negative of a multiplier for the number of rows in the table; for example, a column in which values appear about twice on the average could be represented by <structfield>stadistinct</> = -0.5. Additionally, I think that example is misleading because it's only really true if there are no null values in the column. Perhaps it would help to have a more explicit example to illustrate how nulls affect stadistinct, for example: ... for example, a column in which about 80% of the values are nonnull and each nonnull value appears about twice on average could be represented by <structfield>stadistinct</> = -0.4. Regards, Dean -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers