Re: Migration from MSSQL to POSTGRESQL

In the one Oracle -> Postgresql migration I did (where I came in after the
AWS RDS Postgresql VMs were already sped'ed and were 1:1 the same as the
Oracle servers:
- disk usage was 1/3 lower
- both CPU and RAM were 75% over-specified. (They could be chopped in half
and performance would still be good.)

But, of course, your mileage not only might vary, but *it will vary*.

On Mon, Dec 1, 2025 at 3:38 AM Raj <rajeshkumar(dot)dba09(at)gmail(dot)com> wrote:

> Sorry, it's Oracle to POSTGRESQL migration.
>
> I apologize for the confusion.
>
> Please suggest based on Oracle.
>
> On Mon, 1 Dec 2025, 14:00 Tayyab Fayyaz, <tayyab(dot)humayl(at)gmail(dot)com> wrote:
>
>> Hello Raj,
>>
>> It really depends on how much of those 64 vCPUs and 250GB RAM your SQL
>> Server actually uses today, and whether you’re running on a physical box or
>> a virtual machine.
>>
>> PostgreSQL doesn’t have a 1:1 sizing formula against SQL Server. I’d
>> first look at real CPU/memory usage, workload pattern (OLTP vs reporting),
>> and how connections/queries behave. I’d 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’s a physical server*, I’d start with similar hardware for
>> PostgreSQL and then tune Postgres parameters (shared_buffers, work_mem,
>> etc.) based on monitoring.
>> -
>>
>> *If it’s a VM*, I’d provision a bit more capacity than the current
>> SQL Server allocation to give some headroom for tuning and unexpected
>> overhead, 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 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)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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