RE: Redo I/O size seems much bigger the data write I/O
Date: Thu, 7 Aug 2014 11:16:17 +0800
Message-ID: <0BDF2A25A09ADD40908745EEFC0A0FB6022006B6_at_HKJUMXMB103B.zone1.scb.net>
I would look at the (data) “Block Changes” statistics. You may be repeatedly updating the same data block (each update generating redo) but DBWR only writing the data block to disk after a large number of updates.
Hemant K Chitale
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of amihay gonen
Sent: Wednesday, August 06, 2014 8:29 PM
To: ORACLE-L
Subject: Redo I/O size seems much bigger the data write I/O
Hi all,
in our test machine I see that the ratio between Redo size 1M per second is much lower then the Physical write 78.1 * 8K = 624K
I wonder if it is because our load test program , or also in a typical oracle production , we'll see more redo the Physical writes .
Assuming the following :
- no direct insert (bypassing oracle)
- DB is in archive log (production ...)
Load Profile
Per Second
Per Transaction
Per Exec
Per Call
DB Time(s):
0.8
0.0
0.00
10.03
DB CPU(s):
0.7
0.0
0.00
7.97
Redo size:
1,685,501.9
2,699.9
Logical reads:
8,403.5
13.5
Block changes:
13,908.4
22.3
Physical reads:
0.1
0.0
Physical writes:
78.1
0.1
User calls:
0.1
0.0
Parses:
0.6
0.0
Hard parses:
0.1
0.0
W/A MB processed:
0.0
0.0
Logons:
0.0
0.0
Executes:
12,495.3
20.0
Rollbacks:
0.0
0.0
Transactions:
624.3
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