Re: Extended Statistics set/restore/clear functions.

hi.

select '{"1, 0B100101":"NaN"}'::pg_ndistinct;
pg_ndistinct
------------------------
{"1, 37": -2147483648}
(1 row)

this is not what we expected?
For the VALUE part of pg_ndistinct, float8 has 3 special values: inf, -inf, NaN.

For the key part of pg_ndistinct, see example.
select '{"1, 16\t":"1"}'::pg_ndistinct;
here \t is not tab character, ascii 9. it's two characters: backslash
and character "t".
so here it should error out?
(apply this to \n, \r, \b)

pg_ndistinct_in(PG_FUNCTION_ARGS)
ending part should be:

freeJsonLexContext(lex);
if (result == JSON_SUCCESS)
{
......
}
else
{
ereturn(parse_state.escontext, (Datum) 0,
errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
errmsg("malformed pg_ndistinct: \"%s\"", str),
errdetail("Must be valid JSON."));
PG_RETURN_NULL();
}
result should be either JSON_SUCCESS or anything else.

all these functions:
ndistinct_object_start, ndistinct_array_start,
ndistinct_object_field_start, ndistinct_array_element_start
have
ndistinctParseState *parse = state;

do we need to change it to
ndistinctParseState *parse = (ndistinctParseState *)state;
?

ndistinctParseState need to add to src/tools/pgindent/typedefs.list
probably change it to "typedef struct ndistinctParseState".
also struct ndistinctParseState need placed in the top of
src/backend/statistics/mvdistinct.c
not in line 340?