RE: I/O and db_file_multiblock_read_count
- From: "Kevin Closson" <kevinc@xxxxxxxxxxxxx>
- To: "oracle-l" <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 11 Dec 2006 11:15:23 -0800
Your tests prove that the I/O subsystem drops from
115MB/s to 40MBs if doing a sequential scan of a really
small file. It generally is not the case that larger application
requests result in longer scan times, but it raises some questions:
1. Is users01.dbf the same file invovled in the test reported in the OP?
2. What kind of SAN is under users01.dbf?
3. What kind of LUN is under users01.dbf (e.g., 2 disks RAID 1+0 striped
with 32KB ?)
>>>-----Original Message-----
>>>From: oracle-l-bounce@xxxxxxxxxxxxx
>>>[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Kevin Lidh
>>>Sent: Monday, December 11, 2006 6:39 AM
>>>To: Kevin Closson
>>>Cc: oracle-l
>>>Subject: RE: I/O and db_file_multiblock_read_count
>>>
>>>I apologize for the tardiness of my response. This is the
>>>result of timing the dd. It seems to indicate the same
>>>thing as the scattered read test. Or am I reading that wrong?
>>>
>>>(8k * 16)
>>>Unix> time dd if=/ora/data/bordcdw/users/users01.dbf of=/dev/null
>>>bs=131072
>>>1290+1 records in
>>>1290+1 records out
>>>
>>>real 1.4
>>>user 0.0
>>>sys 0.5
>>>
>>>(8k * 128)
>>>Unix> time dd if=/ora/data/bordcdw/users/users01.dbf of=/dev/null
>>>bs=1048576
>>>161+1 records in
>>>161+1 records out
>>>
>>
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