Monday, June 15, 2009

Resuming and the search for the 4Mb lost

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It's been a while this place has been quiet, not anymore. I changed jobs on February and was on a stabilization process, a very long one if you like, or at least for me.

I missed very much the moment to face the keyboard and share something to you, however since today I'm committing to thoroughly give an update every 2 weeks, at least.

Have you been through the Oracle Server startup process, step by step? Here is an excercise for you:

As you may know, we already have an instance, background processes and memory, after having the database started up in NOMOUNT state. If you don't believe me do the test, best if you try this on a Unix/Linux environment.

1) startup nomount at SQL*Plus prompt.
2) on another OS shell, issue a ps -ef | grep ora_ you'll see all background processes started.
3) now issue an ipcs -m and you'll see all shared memory segments allocated to Oracle server.

Take note the amount of memory allocated for oracle, write down this figure, we'll need it.

Now go all the way and manually go thru all steps of database startup, issue following commands on SQL*Plus.
1) alter database mount
2) alter database open

Now you have all memory allocated to Oracle server, this internally reported set of information provides a grand total labeled "Total System Global Area". If you convert the memory reported by ipcs and this one to bytes, you'll see we have missing 4Mb.

It happens the same on your databases? Somebody has the answer for this result?
I did this test under and on Linux, this behavior may not be present on another releases and/or platforms; please, share with us your results on a comment.

I want to thank you for giving me your attention, hope to see you real soon.

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