Re: Memory sizing - DBA question

Sameer, sorry it took so long to get back to you.

utrankar_at_nyc.pipeline.com (Sameer Utrankar) wrote:

>1. All oracle background processes share the same memory ?
Yes they do, since they are processes thata ctually support the server procesees which are shared by the users accessing the database.

>2. Shadow processes also share the same memory as background proceses
>? Is that why shared memory of shadow process is assumed to be 0 ?
The shadow processes hook into the shared memory taken up by the background processes.

>3. When you run a tool - say sqlplus - shared and private memory of
>it is considered only once - regardless of how many users are running
>the same tool - why ?

In Table 2-2, the figures for sqlplus shared memory (1,781,760) is instance wide and only allocate donce. The private portion (393,216) is per user. Perhaps the way I presented it is confusing!

>4. I always thought in any computer system, memory is always used by
>one or more programs. SGA does not figure anywhere in this calculation
>(and is added later separately) - what does that mean ?
We added the SGA after the fact cause memory requirements are SO EASY to collect for the SGA by the SHOW SGA command in Server Manager.

> Which >process(es) owns SGA ? All background processes ? None ? Why doesn't
>it figure into memory requirement of background processes ?
Good question! We do not really care who "owns" the SGA, but let's say it belongs to the "oracle" UNIX user.

>On HP machine, using Glance Plus, when I look at memory usage of a
>process, it shows RSS and VSS parts (Resident and Virtual) and VSS is
>always more than RSS. Does VSS part include RSS ? Which one do I look
>at for doing the caculations, similar to tuning book ? VSS or RSS ?
>VSS figures seem to be more close to the book for sqlplus.
Sorry, I am unfamailiar with the GlancePlus output. The chapter's exercises and sample calculations are designed to illustrate how one asseses the amount of memory required for Oracle - not the only way to go about doing it. This section was written using HP-UX 9 and HP UX Monitor - a rudimentary character -mode predecessor of Glance.

Michael Abbey

co-author Tuning Oracle Received on Mon Apr 08 1996 - 00:00:00 CEST