IO function metric.

From: Mladen Gogala <gogala.mladen_at_gmail.com>
Date: Tue, 23 Dec 2008 13:22:01 +0000 (UTC)
Message-ID: <giqolp$fn6$2@solani.org>

Oracle 11g has a table called V$IOFUNCMETRIC which is a typical metric table, like the set that was introduced in 10g. What confuses me are 2 things:
1) SQL> select function_name from V$IOFUNCMETRIC;

FUNCTION_NAME

---

Recovery
Direct Writes
Smart Scan
Others
ARCH
DBWR
XDB
Streams AQ
Buffer Cache Reads
Direct Reads
Data Pump
LGWR
RMAN 13 rows selected.

What the heck is "smart scan"? It's neither a buffer cache read nor a direct read since both functions are defined separately.

2) 1 select SMALL_READ_MBPS,SMALL_READ_IOPS   2 from V$IOFUNCMETRIC
  3* where FUNCTION_NAME='LGWR'
SQL> / SMALL_READ_MBPS SMALL_READ_IOPS
--------------- ---------------

     .016650017 1.83150183

Elapsed: 00:00:00.05

LGWR is READING? What is log writer reading? Log writer is not supposed to be reading anything. Why is LGWR doing reads? I consider it to be cheating. Does anybody have any information as to what is LGWR reading? Kevin Closson's explanation from this article http://tinyurl.com/yr37pw obviously does not cover this case.

-- 
Mladen Gogala
http://mgogala.freehostia.com

Received on Tue Dec 23 2008 - 07:22:01 CST