Re: Extended Statistics set/restore/clear functions. - Mailing list pgsql-hackers

On Tue, Nov 11, 2025 at 11:14 PM jian he <jian.universality@gmail.com> wrote:
>
> On Tue, Nov 11, 2025 at 4:07 PM Michael Paquier <michael@paquier.xyz> wrote:
> > I've rebased the full set using the new structure.  0001~0004 are
> > clean.  0005~ need more work and analysis, but that's a start.

hi.

+Datum
+pg_ndistinct_out(PG_FUNCTION_ARGS)
+
+
+ appendStringInfo(&str, "], \"" PG_NDISTINCT_KEY_NDISTINCT "\": %d}",
+ (int) item.ndistinct);

I’m a bit confused about the part above,
item.ndistinct is double type, we just cast it to int type?


after apply 0004, the below in doc/src/sgml/perform.sgml also need to change?

<programlisting>
CREATE STATISTICS stts (dependencies) ON city, zip FROM zipcodes;

ANALYZE zipcodes;

SELECT stxname, stxkeys, stxddependencies
  FROM pg_statistic_ext join pg_statistic_ext_data on (oid = stxoid)
  WHERE stxname = 'stts';
 stxname | stxkeys |             stxddependencies
---------+---------+------------------------------------------
 stts    | 1 5     | {"1 => 5": 1.000000, "5 => 1": 0.423130}
(1 row)
</programlisting>


Do you think it's worth the trouble to have two separate
appendStringInfoChar for ``{}``?

for example in loop ``for (i = 0; i < ndist->nitems; i++)``. we can change to:
        appendStringInfoChar(&str, '{');
        appendStringInfo(&str, "\"" PG_NDISTINCT_KEY_ATTRIBUTES "\": [%d",
                         item.attributes[0]);

        for (int j = 1; j < item.nattributes; j++)
            appendStringInfo(&str, ", %d", item.attributes[j]);

        appendStringInfo(&str, "], \"" PG_NDISTINCT_KEY_NDISTINCT "\": %d",
                         (int) item.ndistinct);
        appendStringInfoChar(&str, '}');


--
jian
https://www.enterprisedb.com/