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Oracle advanced tuning course

From: Juan Carlos Reyes Pacheco <>
Date: Mon, 26 Jul 2004 19:43:03 -0400
Message-Id: <41059707.00001C.01364@CACHITOSS>

Hi list
as you know I'm not an expert, but I think after all this 7 years, and suffering I had in all hte database we installed, I can give a course to teach a new dba tecniques to get an advanced level. I think this is sometimes only to point to the fact some feature exists, I tried to test any thing before giving an opinion, and investigated about. For exapmle I couldn't get oracle use histograms I'll do further investigations.

I have to add several points, but I'll do when I get time, bucause it tookme a lot of time to write it.

I respect other words (something not common or I can't find in documentation using other words) , for examle from this lis I copy cary's comment about RAC, I could change cary's words and write it as if I would had said, but I think this is unethic and stupid, because the day someone askme about it will be obvious that weren't my words. The day I have enough rac expertience to give my opinion I'll replace it.
I don't know too much about copyright any correction will be welcome, I suppose to put the link is enough.

This paper will be free available on my site

This is almost the final draft,is far miles away from my previous paper, this is at least all in english.

Any specific critic is welcome.

sorry, my daily bandwidth is short.

Juan Carlos Reyes Pacheco
-------Original Message-------  

Date: 07/26/04 19:10:53
Subject: Re: 9.2 V$ views  

> (like even analyzing DD in 9.2, etc.)
> Can't that lead us to other problems?

Yep, it can ;)
But in 9.2 it's supported and in 10g it's default anyway...  

Btw, the dba_extents performance problem you mentioned earlier probably comes from the fact that in LMT configuration you can get detailed extent information only from the segment header itself, this means at least one consistent get per segment which you're querying. Given that lots of segment headers aren't in buffer cache, a count(*) on dba_extents may cause thousands of physical IO's, recursive calls and latching...  

SQL> set autot trace stat
SQL> select count(*) from dba_extents;  

1 row selected.    


41228 recursive calls
1 db block gets
20799 consistent gets
3389 physical reads
0 redo size
380 bytes sent via SQL*Net to client
511 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed  

So, dba_extents is a quite dangerous view to query in LMT environment.  


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Received on Mon Jul 26 2004 - 18:44:10 CDT

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