>The almost session memory is used for catalog caches. So you should to have big catalog and long living sessions.
>What do you do exactly?
I've generate test code that emulates instruction tree size for our production code. This test shows: -What is the size of instruction tree for our typical BP it's greater than 300M for each session -How often do PostgreSql parse the text When postgres clean cache, so much often
PostgreSQL parses the source code of functions once per session
So Oracle is much better in this case. It's very difficult really estimate in such case, to buy Oracle or to by hardware.
Should be - The implementation of PLpgSQL and PL/SQL is strongly different. When your case is not usual, then the migration to Postgres needs redesign sometimes.