Re: Migration from MSSQL to POSTGRESQL

Hi Ron, it's On premises. Not cloud.

On Mon, 1 Dec 2025, 20:15 Ron Johnson, <ronljohnsonjr(at)gmail(dot)com> wrote:

>
> 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
>>>>
>>>>
>>>>
>
> --
> Death to <Redacted>, and butter sauce.
> Don't boil me, I'm still alive.
> <Redacted> lobster!
>