Re: 9.2 V$ views

From: Tanel Põder <tanel.poder.003_at_mail.ee>
Date: Tue, 27 Jul 2004 02:12:31 +0300
Message-ID: <399d01c47366$070a9910$0a879fd9@porgand>

> (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.

Statistics

---

      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.

Tanel.

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Received on Mon Jul 26 2004 - 18:09:56 CDT