Re: [PATCH] Add pg_get_database_ddl() function to reconstruct CREATE DATABASE statement

On Wed, Nov 19, 2025 at 3:48 PM Japin Li <japinli(at)hotmail(dot)com> wrote:

>
> Hi Akshay,
>
> Thanks for updating the patch.
>
> On Tue, 18 Nov 2025 at 13:33, Akshay Joshi <akshay(dot)joshi(at)enterprisedb(dot)com>
> wrote:
> > Hi Chao
> >
> > Thanks for reviewing my patch.
> >
> > On Tue, Nov 18, 2025 at 5:59 AM Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com> wrote:
> >
> > Hi Akshay,
> >
> > I just reviewed v3 and got some comments:
> >
> > > On Nov 17, 2025, at 22:34, Akshay Joshi <
> akshay(dot)joshi(at)enterprisedb(dot)com> wrote:
> > >
> > > All the review comments have been addressed in v3 patch.
> >
> > 1 - ruleutils.c
> > ```
> > + if (dbForm->datconnlimit != 0)
> > + get_formatted_string(&buf, prettyFlags, 1, "CONNECTION
> LIMIT = %d",
> > +
> dbForm->datconnlimit);
> > ```
> >
> > I think this is wrong. Default value of CONNECTION_LIMIT is -1 rather
> than 0. 0 means no connection is allowed, users
> > should intentionally set the value, thus 0 should be printed.
> >
> > 2 - ruleutils.c
> > ```
> > + if (!attrIsNull)
> > + get_formatted_string(&buf, prettyFlags, 1, "ICU_RULES =
> %s",
> > +
> quote_identifier(TextDatumGetCString(dbValue)));
> > ```
> >
> > ICU_RULES should be omitted if provider is not icu.
> >
> > 3 - ruleutils.c
> > ```
> > + if (!HeapTupleIsValid(tupleDatabase))
> > + ereport(ERROR,
> > + errcode(ERRCODE_UNDEFINED_OBJECT),
> > + errmsg("database with oid %d does not
> exist", dbOid));
> > ```
> >
> > I believe all existing code use %u to format oid. I ever raised the
> same comment to the other get_xxx_ddl patch.
> >
> > Fixed all above in the attached v4 patch.
>
> 1.
> Since the STRATEGY and OID parameters are not being reconstructed, should
> we
> document this behavior?
>
> postgres=# CREATE DATABASE mydb WITH STRATEGY file_copy OID 19876
> IS_TEMPLATE true;
> CREATE DATABASE
> postgres=# SELECT pg_get_database_ddl('mydb', true);
> pg_get_database_ddl
> --------------------------------------------
> CREATE DATABASE mydb +
> WITH OWNER = japin +
> ENCODING = "UTF8" +
> LC_COLLATE = "en_US.UTF-8"+
> LC_CTYPE = "en_US.UTF-8" +
> COLLATION_VERSION = "2.39"+
> LOCALE_PROVIDER = 'libc' +
> TABLESPACE = pg_default +
> ALLOW_CONNECTIONS = true +
> CONNECTION LIMIT = -1 +
> IS_TEMPLATE = true;
> (1 row)
>

The FormData_pg_database structure does not expose the database *STRATEGY*,
and reconstructing the *OID* serves no practical purpose. If the majority
agrees, I can extend the DDL to include OID.

>
> 2.
> We can restrict the scope of the dbTablespace variable as follows:
>
> + if (OidIsValid(dbForm->dattablespace))
> + {
> + char *dbTablespace =
> get_tablespace_name(dbForm->dattablespace);
> + if (dbTablespace)
> + get_formatted_string(&buf, prettyFlags, 2,
> "TABLESPACE = %s",
> +
> quote_identifier(dbTablespace));
> + }
>

Will fix this in the next patch.

>
> > >
> > > 7 - For those parameters that have default values should be omitted.
> For
> > > example:
> > > ```
> > > evantest=> select pg_get_database_ddl('evantest', true);
> > > pg_get_database_ddl
> > > ------------------------------------
> > > CREATE DATABASE evantest +
> > > WITH +
> > > OWNER = chaol +
> > > ENCODING = "UTF8" +
> > > LC_COLLATE = "en_US.UTF-8"+
> > > LC_CTYPE = "en_US.UTF-8" +
> > > LOCALE_PROVIDER = 'libc' +
> > > TABLESPACE = pg_default +
> > > ALLOW_CONNECTIONS = true +
> > > CONNECTION LIMIT = -1;
> > > (1 row)
> > > ```
> > >
> > > I created the database “evantest” without providing any parameter. I
> think
> > > at least OWNER, TABLESPACE and ALLOW_CNONNECTIONS should be omitted.
> For
> > > CONNECTION LIMIT, you already have a logic to omit it but the logic has
> > > some problem as comment 1.
> > >
> >
> >
> >
> > IMHO, parameters with default values *should not* be omitted from the
> > output of the pg_get_xxx_ddl functions. The primary purpose of these
> > functions is to accurately reconstruct the DDL. Including all parameters
> > ensures clarity, as not everyone is familiar with the default value of
> > every single parameter.
>
> +1
>
> --
> Regards,
> Japin Li
> ChengDu WenWu Information Technology Co., Ltd.
>