Re: Linux VM Sizing
| От | Rui DeSousa |
|---|---|
| Тема | Re: Linux VM Sizing |
| Дата | |
| Msg-id | CC1E9024-425D-43EE-AB91-A8B323104E87@icloud.com обсуждение исходный текст |
| Ответ на | Linux VM Sizing (Sam Stearns <sam.stearns@dat.com>) |
| Список | pgsql-admin |
On Jul 28, 2025, at 7:41 PM, Sam Stearns <sam.stearns@dat.com> wrote:Howdy,We are sizing a Linux VM to migrate our Oracle production database to. We are currently running on an Oracle Database Appliance. Oracle CPU / memory usage stats are:CPU % usage - 25% of 20 cores / 40 threads (Intel® Xeon® S4314 processor)Memory % usage - 100% usage of 600G SGABased on the above can anyone give advice as to how to size the CPU / memory of the Linux VM, please?
It really depends on your application. For an Oracle to Postgres migration we estimated Postgres at 80% of Oracle and purchased larger system based on that metric.
We still had some initial performance issues. Oracle is very forgiving of bad code.
Here’s is some of the issues that I ran into that had to be address. The project was circa was with Postgres 9.6.
1. Rewriting of poorly written views; i.e. view nested on top of other views all access the same table underlying tables, etc
2. Hints —Rewriting some queries to influence the planner to choose better execution plan (i.e. leading table, etc). Postgres does not have hints.
4. Some queries needed to be rewritten to make use of fencing; i.e. using materialized CTE to improve performance.
5. Exception handling - exception handling makes use of xid’s; thus our transaction ids wrap arounds where occurring every other month.
We slowly replaced the exception handling code as a lot of was not needed with Postgres; reducing our transaction wrap around to just over a year.
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