Re: +(pg_lsn, int8) and -(pg_lsn, int8) operators

On Tue, Apr 28, 2020 at 12:56:19PM +0900, Fujii Masao wrote:
> Yes. Attached is the updated version of the patch, which introduces
> +(pg_lsn, numeric) and -(pg_lsn, numeric) operators.
> To implement them, I added also numeric_pg_lsn() function that converts
> numeric to pg_lsn.

-    those write-ahead log locations.
+    those write-ahead log locations. Also the number of bytes can be added
+    into and substracted from LSN using the + and
+    - operators, respectively.
That's short.  Should this mention the restriction with numeric (or
just recommend its use) because we don't have a 64b unsigned type
internally, basically Robert's point? 

+   /* XXX would it be better to return NULL? */
+   if (NUMERIC_IS_NAN(num))
+       ereport(ERROR,
+               (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                errmsg("cannot convert NaN to pg_lsn")));
That would be good to test, and an error sounds fine to me.
--
Michael