Re: support fast default for domain with constraints - Mailing list pgsql-hackers

On Thu, Mar 12, 2026 at 3:50 AM Andrew Dunstan <andrew@dunslane.net> wrote:

Also added some tests.

V11 looks good to me.


On Wed, Mar 11, 2026 at 6:34 PM Viktor Holmberg <v@viktorh.net> wrote:

I’ve been burned my this issue in the past so would be great if this could get in.

+ /*
+ * If the domain has volatile constraints, we must do a table rewrite
+ * since the constraint result could differ per row and cannot be
+ * evaluated once and cached as a missing value.
+ */
+ if (has_volatile)
+ {
+ Assert(has_domain_constraints);
+ tab->rewrite |= AT_REWRITE_DEFAULT_VAL;
+ }

I'm not sure. But seems to me this makes the pre-existing guard for virtual columns
redundant?
I mean this code on line 7633:
if (colDef->generated != ATTRIBUTE_GENERATED_VIRTUAL)
tab->rewrite |= AT_REWRITE_DEFAULT_VAL;

If the first `if (has_volatile)` is false, then

if (colDef->generated != ATTRIBUTE_GENERATED_VIRTUAL)
tab->rewrite |= AT_REWRITE_DEFAULT_VAL;

is still reachable.

Also, perhaps virtual generated columns could use a test?

Virtual generated columns based on domain are not currently supported.
I have a patch for it: https://commitfest.postgresql.org/patch/5725
but it's not doable now because of
https://git.postgresql.org/cgit/postgresql.git/commit/?id=0cd69b3d7ef357f2b43258de5831c4de0bd51dec
You may also be interested in https://commitfest.postgresql.org/patch/5907

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