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From: me nefcanto <sn.1361@gmail.com>
Date: Wed, 5 Mar 2025 14:18:20 +0330
Message-ID: <CAEHBEOBNoG8RkKuCcQQWkbYppMLMzA0MXq+s0kZ6wKWgD7+45Q@mail.gmail.com>
Subject: Re: Quesion about querying distributed databases
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Adrian Klaver <adrian.klaver@aklaver.com>, pgsql-general@lists.postgresql.org
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Dear Laurenz,

That means a solid monolith database. We lose many goodies with that. As a
real-world example, right now we can import a single database from the
production to the development to test and troubleshoot data.

What if we host all databases on the same server and use FDW. What happens
in that case? Does it return 100 thousand records and join in the memory?

Because in SQL Server, when you perform a cross-database query (not
cross-server) the performance is extremely good, proving that it does not
return 100 thousand ItemId from Taxonomy.ItemCategories to join with
ProductId.

Is that the same case with Postgres too, If databases are located on one
server?

Regards
Saeed

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<div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:tahoma,s=
ans-serif">Dear Laurenz,=C2=A0</div><div class=3D"gmail_default" style=3D"f=
ont-family:tahoma,sans-serif"><br></div><div class=3D"gmail_default" style=
=3D"font-family:tahoma,sans-serif">That means a solid monolith database. We=
 lose many goodies with that. As a real-world example, right now we can imp=
ort a single database from the production to the development to test and tr=
oubleshoot data.</div><div class=3D"gmail_default" style=3D"font-family:tah=
oma,sans-serif"><br></div><div class=3D"gmail_default" style=3D"font-family=
:tahoma,sans-serif">What if we host all databases on the same server and us=
e FDW. What happens in that case? Does it return 100 thousand records and j=
oin in the memory?</div><div class=3D"gmail_default" style=3D"font-family:t=
ahoma,sans-serif"><br></div><div class=3D"gmail_default" style=3D"font-fami=
ly:tahoma,sans-serif">Because in SQL Server, when you perform a cross-datab=
ase query (not cross-server) the performance is extremely good, proving tha=
t it does not return 100 thousand ItemId from Taxonomy.ItemCategories to jo=
in with ProductId.</div><div class=3D"gmail_default" style=3D"font-family:t=
ahoma,sans-serif"><br></div><div class=3D"gmail_default" style=3D"font-fami=
ly:tahoma,sans-serif">Is that the same case with Postgres too, If databases=
 are located on one server?</div><div class=3D"gmail_default" style=3D"font=
-family:tahoma,sans-serif"><br></div><div class=3D"gmail_default" style=3D"=
font-family:tahoma,sans-serif">Regards</div><div class=3D"gmail_default" st=
yle=3D"font-family:tahoma,sans-serif">Saeed</div></div>

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