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From: Tayyab Fayyaz <tayyab.humayl@gmail.com>
Date: Mon, 1 Dec 2025 00:27:59 -0800
Message-ID: 
 <CAFVRaQ2zxmVY+zqADEv2hqo9uR6Q-iYn0v2MQ2EKUtv+yRZKsA@mail.gmail.com>
Subject: Re: Migration from MSSQL to POSTGRESQL
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Raj <rajeshkumar.dba09@gmail.com>,
	Pgsql-admin <pgsql-admin@lists.postgresql.org>
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Hello Raj,

It really depends on how much of those 64 vCPUs and 250GB RAM your SQL
Server actually uses today, and whether you=E2=80=99re running on a physica=
l box or
a virtual machine.

PostgreSQL doesn=E2=80=99t have a 1:1 sizing formula against SQL Server. I=
=E2=80=99d first
look at real CPU/memory usage, workload pattern (OLTP vs reporting), and
how connections/queries behave. I=E2=80=99d also factor in how well we can =
migrate
and map the data types and queries, because good type choices and query
rewrites can significantly reduce resource usage.

   -

   *If it=E2=80=99s a physical server*, I=E2=80=99d start with similar hard=
ware for
   PostgreSQL and then tune Postgres parameters (shared_buffers, work_mem,
   etc.) based on monitoring.
   -

   *If it=E2=80=99s a VM*, I=E2=80=99d provision a bit more capacity than t=
he current SQL
   Server allocation to give some headroom for tuning and unexpected overhe=
ad,
   and then right-size after observing the real load in PostgreSQL.

Once the migration is done and in steady use, we can monitor CPU, memory,
and I/O in PostgreSQL and then optimise or scale down/up based on real
metrics instead of guessing up front.


Tayyab

On Sun, Nov 30, 2025 at 11:14=E2=80=AFPM Laurenz Albe <laurenz.albe@cyberte=
c.at>
wrote:

> On Mon, 2025-12-01 at 08:46 +0530, Raj wrote:
> > I am migrating from MSSQL to POSTGRESQL. In MSSQL, I am using 64 vCPU
> and 250GB RAM.
> > Now how much we can give in postgres?
>
> If these specifications worked for you with Microsoft SQL Server, use the
> same
> with PostgreSQL.  If you can, don't use Windows.
>
> Yours,
> Laurenz Albe
>
>
>

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<div dir=3D"ltr"><div dir=3D"ltr">Hello Raj,<div><br></div><div><p>It reall=
y depends on how much of those 64 vCPUs and 250GB RAM your SQL Server actua=
lly uses today, and whether you=E2=80=99re running on a physical box or a v=
irtual machine.</p>
<p>PostgreSQL doesn=E2=80=99t have a 1:1 sizing formula against SQL Server.=
 I=E2=80=99d first look at real CPU/memory usage, workload pattern (OLTP vs=
 reporting), and how connections/queries behave. I=E2=80=99d also factor in=
 how well we can migrate and map the data types and queries, because good t=
ype choices and query rewrites can significantly reduce resource usage.</p>
<ul>
<li>
<p><strong>If it=E2=80=99s a physical server</strong>, I=E2=80=99d start wi=
th similar hardware for PostgreSQL and then tune Postgres parameters (share=
d_buffers, work_mem, etc.) based on monitoring.</p>
</li>
<li>
<p><strong>If it=E2=80=99s a VM</strong>, I=E2=80=99d provision a bit more =
capacity than the current SQL Server allocation to give some headroom for t=
uning and unexpected overhead, and then right-size after observing the real=
 load in PostgreSQL.</p>
</li>
</ul>
<p>Once the migration is done and in steady use, we can monitor CPU, memory=
, and I/O in PostgreSQL and then optimise or scale down/up based on real me=
trics instead of guessing up front.</p></div><div><span style=3D"color:rgb(=
0,0,0)"><br></span></div><div><span style=3D"color:rgb(0,0,0)"><br></span><=
/div><div><span style=3D"color:rgb(0,0,0)">Tayyab</span></div></div><br><di=
v class=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr" class=3D"gma=
il_attr">On Sun, Nov 30, 2025 at 11:14=E2=80=AFPM Laurenz Albe &lt;<a href=
=3D"mailto:laurenz.albe@cybertec.at">laurenz.albe@cybertec.at</a>&gt; wrote=
:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.=
8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On Mon, 2025-1=
2-01 at 08:46 +0530, Raj wrote:<br>
&gt; I am migrating from MSSQL to POSTGRESQL. In MSSQL, I am using 64 vCPU =
and 250GB RAM.<br>
&gt; Now how much we can give in postgres?<br>
<br>
If these specifications worked for you with Microsoft SQL Server, use the s=
ame<br>
with PostgreSQL.=C2=A0 If you can, don&#39;t use Windows.<br>
<br>
Yours,<br>
Laurenz Albe<br>
<br>
<br>
</blockquote></div></div>

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