Re: Synchronizing slots from primary to standby

On Fri, Feb 2, 2024 at 9:50 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>
> Here are some review comments for v750001.
>
> ~~~
>
> 2.
> This patch also implements a new API libpqrcv_get_dbname_from_conninfo()
> to extract database name from the given connection-info
>
> ~
>
> /extract database name/the extract database name/
>

I think it should be "..extract the database name.."

> ======
> .../libpqwalreceiver/libpqwalreceiver.c
>

>
> 4. libpqrcv_connect
>
> /*
> - * Establish the connection to the primary server for XLOG streaming
> + * Establish the connection to the primary server.
> + *
> + * The connection established could be either a replication one or
> + * a non-replication one based on input argument 'replication'. And further
> + * if it is a replication connection, it could be either logical or physical
> + * based on input argument 'logical'.
>
> That first comment ("could be either a replication one or...") seemed
> a bit meaningless (e.g. it like saying "this boolean argument can be
> true or false") because it doesn't describe what is the meaning of a
> "replication connection" versus what is a "non-replication
> connection".
>

The replication connection is a term already used in the code and
docs. For example, see the error message: "pg_hba.conf rejects
replication connection for host ..". It means that for communication
the connection would use replication protocol instead of the normal
(one used by queries) protocol. The other possibility could be to
individually explain each parameter but I think that is not what we
follow in this or related functions. I feel we can use a simple
comment like: "This API can be used for both replication and regular
connections."

> ~~~
>
> 5.
> /* We can not have logical without replication */
> Assert(replication || !logical);
>
> if (replication)
> {
> keys[++i] = "replication";
> vals[i] = logical ? "database" : "true";
>
> if (!logical)
> {
> /*
> * The database name is ignored by the server in replication mode,
> * but specify "replication" for .pgpass lookup.
> */
> keys[++i] = "dbname";
> vals[i] = "replication";
> }
> }
>
> keys[++i] = "fallback_application_name";
> vals[i] = appname;
> if (logical)
> {
> ...
> }
>
> ~
>
> The Assert already says we cannot be 'logical' if not 'replication',
> therefore IMO it seemed strange that the code was not refactored to
> bring that 2nd "if (logical)" code to within the scope of the "if
> (replication)".
>
> e.g. Can't you do something like this:
>
> Assert(replication || !logical);
>
> if (replication)
> {
> ...
> if (logical)
> {
> ...
> }
> else
> {
> ...
> }
> }
> keys[++i] = "fallback_application_name";
> vals[i] = appname;
>

+1.

> ~~~
>
> 6. libpqrcv_get_dbname_from_conninfo
>
> + for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
> + {
> + /*
> + * If multiple dbnames are specified, then the last one will be
> + * returned
> + */
> + if (strcmp(opt->keyword, "dbname") == 0 && opt->val &&
> + opt->val[0] != '\0')
> + dbname = pstrdup(opt->val);
> + }
>
> Should you also pfree the old dbname instead of gathering a bunch of
> strdups if there happened to be multiple dbnames specified ?
>
> SUGGESTION
> if (strcmp(opt->keyword, "dbname") == 0 && opt->val && *opt->val)
> {
> if (dbname)
> pfree(dbname);
> dbname = pstrdup(opt->val);
> }
>

makes sense and shouldn't we need to call PQconninfoFree(opts); at the
end of libpqrcv_get_dbname_from_conninfo() similar to
libpqrcv_check_conninfo()?

--
With Regards,
Amit Kapila.