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From: Ajin Cherian <itsajin@gmail.com>
Date: Wed, 21 Feb 2024 16:28:36 +1100
Message-ID: <CAFPTHDbSwRNc=37_JpeJGq36_m-5ebEGTd9hXiutof+tnqt4vg@mail.gmail.com>
Subject: Re: Have pg_basebackup write "dbname" in "primary_conninfo"?
To: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, "barwick@gmail.com" <barwick@gmail.com>, 
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, 
	"robertmhaas@gmail.com" <robertmhaas@gmail.com>
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On Wed, Feb 21, 2024 at 4:09=E2=80=AFPM Hayato Kuroda (Fujitsu) <
kuroda.hayato@fujitsu.com> wrote:

> Dear Horiguchi-san,
>
> > GetConnection()@streamutil.c wants to ensure conninfo has a fallback
> > database name ("replication"). However, the function seems to be
> > ignoring the case where neither dbname nor connection string is given,
> > which is the first case Kuroda-san raised. The second case is the
> > intended behavior of the function.
> >
> > >     /* pg_recvlogical uses dbname only; others use connection_string
> only.
> > */
> > >     Assert(dbname =3D=3D NULL || connection_string =3D=3D NULL);
> >
> > And the function incorrectly assumes that the connection string
> > requires "dbname=3Dreplication".
> >
> > >      * Merge the connection info inputs given in form of connection
> string,
> > >      * options and default values (dbname=3Dreplication,
> replication=3Dtrue,
> > etc.)
> >
> > But the name is a pseudo database name only used by pg_hba.conf
> > (maybe) , which cannot be used as an actual database name (without
> > quotation marks, or unless it is actually created). The function
> > should not add the fallback database name because the connection
> > string for physical replication connection doesn't require the dbname
> > parameter. (attached patch)
>
> I was also missing, but the requirement was that the dbname should be
> included
> only when the dbname option was explicitly specified [1]. Even mine and
> yours
> cannot handle like that. Libpq function
> PQconnectdbParams()->pqConnectOptions2()
> fills all the parameter to PGconn, at that time the information whether i=
t
> is
> intentionally specified or not is discarded. Then,
> GenerateRecoveryConfig() would
> just write down all the connection parameters from PGconn, they cannot
> recognize.
>
> Well, one option is that if a default dbname should be written to the
configuration file, then "postgres' is a better option than "replication"
or "username" as the default option, at least a db of that name exists.

regards,
Ajin Cherian
Fujitsu Australia

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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote">=
<div dir=3D"ltr" class=3D"gmail_attr">On Wed, Feb 21, 2024 at 4:09=E2=80=AF=
PM Hayato Kuroda (Fujitsu) &lt;<a href=3D"mailto:kuroda.hayato@fujitsu.com"=
>kuroda.hayato@fujitsu.com</a>&gt; wrote:<br></div><blockquote class=3D"gma=
il_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,2=
04,204);padding-left:1ex">Dear Horiguchi-san,<br>
<br>
&gt; GetConnection()@streamutil.c wants to ensure conninfo has a fallback<b=
r>
&gt; database name (&quot;replication&quot;). However, the function seems t=
o be<br>
&gt; ignoring the case where neither dbname nor connection string is given,=
<br>
&gt; which is the first case Kuroda-san raised. The second case is the<br>
&gt; intended behavior of the function.<br>
&gt; <br>
&gt; &gt;=C2=A0 =C2=A0 =C2=A0/* pg_recvlogical uses dbname only; others use=
 connection_string only.<br>
&gt; */<br>
&gt; &gt;=C2=A0 =C2=A0 =C2=A0Assert(dbname =3D=3D NULL || connection_string=
 =3D=3D NULL);<br>
&gt; <br>
&gt; And the function incorrectly assumes that the connection string<br>
&gt; requires &quot;dbname=3Dreplication&quot;.<br>
&gt; <br>
&gt; &gt;=C2=A0 =C2=A0 =C2=A0 * Merge the connection info inputs given in f=
orm of connection string,<br>
&gt; &gt;=C2=A0 =C2=A0 =C2=A0 * options and default values (dbname=3Dreplic=
ation, replication=3Dtrue,<br>
&gt; etc.)<br>
&gt; <br>
&gt; But the name is a pseudo database name only used by pg_hba.conf<br>
&gt; (maybe) , which cannot be used as an actual database name (without<br>
&gt; quotation marks, or unless it is actually created). The function<br>
&gt; should not add the fallback database name because the connection<br>
&gt; string for physical replication connection doesn&#39;t require the dbn=
ame<br>
&gt; parameter. (attached patch)<br>
<br>
I was also missing, but the requirement was that the dbname should be inclu=
ded<br>
only when the dbname option was explicitly specified [1]. Even mine and you=
rs<br>
cannot handle like that. Libpq function PQconnectdbParams()-&gt;pqConnectOp=
tions2()<br>
fills all the parameter to PGconn, at that time the information whether it =
is<br>
intentionally specified or not is discarded. Then, GenerateRecoveryConfig()=
 would<br>
just write down all the connection parameters from PGconn, they cannot reco=
gnize.<br>
<br></blockquote></div><div class=3D"gmail_quote">Well, one option is that =
if a default dbname should be written to the configuration file, then &quot=
;postgres&#39; is a better option than &quot;replication&quot; or &quot;use=
rname&quot; as the default option, at least a db of that name exists.</div>=
<div class=3D"gmail_quote"><br></div><div class=3D"gmail_quote">regards,</d=
iv><div class=3D"gmail_quote">Ajin Cherian</div><div class=3D"gmail_quote">=
Fujitsu Australia<br></div></div>

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