Re: I/O issues on DB 11g
- From: David Fitzjarrell <oratune@xxxxxxxxx>
- To: "dramirezr@xxxxxxxxx" <dramirezr@xxxxxxxxx>, "'oracle-l@xxxxxxxxxxxxx' \(oracle-l@xxxxxxxxxxxxx\)" <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 23 Apr 2014 13:54:12 -0700 (PDT)
Since you have both the controlfiles and the redo logs on the same disk as the
database that is likely impacting the I/O operations for the database; db
files are random-access, scattered read and write files and the
controlfiles/redo logs are sequential read/write files. Think about this for a
moment; you're mixing write patterns and that can slow down the datafile
reads/writes as you wait for the disk heads to finish a redo or controlfile
entry; the opposite is also true as controlfile/redo writes wait on datafifle
processing. It's not an ideal situation.
You might consider having a disk solely for controlfiles and redo logs.
David Fitzjarrell
Primary author, "Oracle Exadata Survival Guide"
On Wednesday, April 23, 2014 2:40 PM, David Ramírez Reyes <dramirezr@xxxxxxxxx>
wrote:
Hi All,
This is the environment.
Windows 2008 R1 Standard, Oracle DB 11g Standard R2, 8 cpu's, 16 GB of physical
memory, 3 disk drives (1 for the OS, 1 for db files, 1 for backups).
Now the problem:
Since we went live with the 11g system about 1 year ago (we used to be on a
very old and horrible 8i -don't ask why-), we have been receiving Email alerts
about Disk Utilization; at the beginning I thought it should be a bug of the R2
version as I wrongly understood it was referring about filesystem space, which
is not a problem.
After several months of 5 or 8 daily mails, I decided to look at it on detail
and check what was necessary to drop off that "false alarm".
After Goggling, I realized that the alarm is not related to disk space, but I/O
reads, as we have 3 db's on the same disk drive, each of them with 20 db files
(the biggest DB has datafiles of about 6 GB, the smallest about 2 GB).
The problem is not really "critical" now because general performance is "good"
(we have more than a year with it!), but that of course does not mean it has to
keep on with those problems (and that alarm is starting causing me headaches
also!).
The first two things I though were increasing the PGA size in order to reduce
Virtual Memory usage (and, I/O as consequence) and add 2 more disk drives to
split the db files of each db into a single and dedicated filesystem; I was
also thinking about tuning some high I/O queries, but don't think the
difference could be huge...
Any ideas or suggestions?
Thanks
David Ramírez
Other related posts:
