Re: pg_rewind with --write-recovery-conf option doesn't write dbname to primary_conninfo value.

On Mon, Feb 3, 2025 at 4:50 PM Hayato Kuroda (Fujitsu)
<kuroda(dot)hayato(at)fujitsu(dot)com> wrote:
>
> Dear Sawada-san,
>
> > I think it's a good idea to support it at least on HEAD. I've attached
> > a patch for that.
>
> +1. I've confirmed that pg_rewind and -R can't output dbname for now,
> and your patch allows to do it.
>
> Few comments for your patch.
>
> 1.
>
> pg_basebackup.sgml has below description. I feel this can be ported to
> pg_rewind.sgml as well.
>
> ```
> The dbname will be recorded only if the dbname was
> specified explicitly in the connection string or <link linkend="libpq-envars">
> environment variable</link>.
> ```
>
> 2.
> I'm not sure whether recovery_gen.h/c is a correct place for the exported function
> GetDbnameFromConnectionOptions(). The function itself does not handle
> postgresql.cuto.conf file.
> I seeked other header files and felt that connect_utils.h might be.
>
> ```
> /*-------------------------------------------------------------------------
> *
> * Facilities for frontend code to connect to and disconnect from databases.
> ```
>
> Another idea is to change the third API to accept the whole connection string, and
> it extracts dbname from it. In this approach we can make GetDbnameFromConnectionOptions()
> to static function - which does not feel strange for me.
>
> Best regards,
> Hayato Kuroda
> FUJITSU LIMITED
>

Hi Sawada-san, h

Here are a few more minor comments in addition to what Kuroda-San
already posted.

======
typo in patch name /primary_conninfo/primary_connifo/

======
Commit message

no details.
bad link.

======
src/fe_utils/recovery_gen.c

1.
static char *
FindDbnameInConnParams(PQconninfoOption *conn_opts)

There is a missing forward declaration of this function. Better to add
it for consistency because the other static function has one.

~~~

2.
+static char *
+FindDbnameInConnParams(PQconninfoOption *conn_opts)
+{
+ PQconninfoOption *conn_opt;
+
+ for (conn_opt = conn_opts; conn_opt->keyword != NULL; conn_opt++)
+ {
+ if (strcmp(conn_opt->keyword, "dbname") == 0 &&
+ conn_opt->val != NULL && conn_opt->val[0] != '\0')
+ return pg_strdup(conn_opt->val);
+ }
+ return NULL;
+}

2a.
I know you copied this, but it seems a bit strange that this function
is named "Params" when everything about it including its parameter and
comments and the caller talks about "_opts" or "Options"

~

2b.
I know you copied this, but normally 'conn_opt' might have been
written as a for-loop variable.

~~~

3.
+/*
+ * GetDbnameFromConnectionOptions
+ *
+ * This is a special purpose function to retrieve the dbname from either the
+ * 'connstr' specified by the caller or from the environment variables.
+ *
+ * Returns NULL, if dbname is not specified by the user in the above
+ * mentioned connection options.
+ */

What does "in the above mentioned connection options" mean? In the
original function comment where this was copied from there was an
extra sentence ("We follow ... from various connection options.") so
this had more context, but now that the other sentence is removed
maybe "above mentioned connection options" looks like it also needs
rewording.

======
Kind Regards,
Peter Smith.
Fujitsu Australia