While having more docs around extra_float_digits is a great idea, I don't think the patch really clarifies much.
(Disclaimer: I honestly have only a vague idea of the reasoning behind extra_float_digits existing in the first place, but perhaps that means I'm a good target audience for the doc patch. Also, I apologize if anything below sounds abrasive--having worked on both my own driver and a few things here and there on the JDBC one, plus running into this in assorted places in the wild, I still find extra_float_digits baffling at best. I immensely appreciate the effort to make improvements here.) That is, the patch explains some of the reasoning behind the setting, but it doesn't really help the reader identify where setting this is useful and/or necessary. E.g., the JDBC driver just indiscriminately sets extra_float_digits to 3 if the server supports it (the max allowable). Is this a bogus approach? + The (inherently inaccurate) textual representation of a <type>real</type> + or <type>double precision</type> value... Isn't full fidelity possible assuming sensible rounding semantics and enough characters of precision? Isn't that the point of extra_float_digits? + will by default contain only as many + significant digits as can be represented without losing precision + on any platform supported by PostgreSQL. How would providing more digits lose precision? Platform as in a non-IEEE 754 server restoring a dump? A non-IEEE 754 client running queries? Something more subtle? And how does having more precision in the serialized cause these to lose precision when decoding the value? I think extra_float_digits is an awkward, surprising implementation detail--at first glance it seems like a "flip this switch for correct behavior" knob. I'd love to have a clear explanation in the docs of why it's needed, and when you should and should not set it (e.g., is the JDBC driver wrong to set it all the time? should every driver set it all the time?). Thanks, Maciek -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
