Can Performance be effect by setting db_file_simultaneous_writes to high

Today we set the parameter db_file_simultaneous_writes to high from default to 32.
db_writer_processes = 4
db_block_lru_latches = 8
disk_async_io=TRUE (we use rawdevices)
number cpu's = 8
The disc util is 100% on the index area. There are 14 process inserting into one table 7 milj records a day. We see that the database writers are the 4 top disk io users.
I was thinking to set the db_writer_processes to 8, so perhaps the contention on the database writers is not so heavy.
Please your thought and stuff i can use to analyze this further.
Thanks

On Page 5, second paragraph under "SEQUENTIAL IO IS
TREATED SPECIALLY BY ORACLE" section of
<a
href="http://www.oracle.com/technology/deploy/availabi
lity/pdf/oow2000_same.pdf"> OPTIMAL STORAGE
CONFIGURATION MADE EASY
</a> document says:
"To achieve this, parameters such as
db_file_multiblock_read_count
should be set to one megabyte, stripe widths should
be set to one megabyte,
and OS IO size limits should be set to at least one
megabyte."
You usually need to check the date and context of articles like this.
Unfortunately this article isn't dated, but you get some clues from the figures it gives for disk latency and transfer rates, and there is a reference to Oracle 8.1 - I think this article is around 10 years old.
As far as context - the point you quote comes from a section that suggests that it applies if you need to make your large reads efficient. In other words, you are expecting, or want, to see a lot of tablescan activity - which would be consistent with the type of system where you would want to set the db_file_mulitblock_read_count high.
You're point, though, is correct - if you set a large value for the db_file_multiblock_read_count then you encourage the (older) cost based optimizer towards tablescans and index fast full scans. In 8i you counterbalance this by carefully reducing the optimizer_index_cost_adj; from 9i onwards you address the side-effects by enabling system statistics (aka CPU costing), and in 10g you don't set the db_file_multiblock_read_count at all - but let Oracle decide on values for the "optimizer read count" and the "run time read count".
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk

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Late last friday (11/6) suddenly started getting the following error messages on a specific set of images imported into iPhoto from an external Hard Drive:
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• can be edited by iPhoto (see more info below)
But this obviously makes me nervous about the integrity of my photo library (i do have time machine and some disc media backups of many (not all, yet) albums, but still ...
CONFOUNDING FACTORS
1. Despite the error message:
• the image preview appears (not an "!" or "?") before and after dismissal of the message
• I can continue on to edit the image from the preview step.
• I can right click on the preview, select "Show Original File" and iPhoto locates the original image in the iPhoto Library Package file.
2. It does not appear if:
• I ignore the message and continue on to to edit the image
• I preview the image in the "Library > Events" index section.
• I preview the image in the "Recent > Last Import" index section.
3. Trashing, and emptying trash (from any index view) then re-importing them hasn't helped.
4. All offending photos can be opened, viewed and edited in various image viewers, editors (Preview.app, the Finder Quickview, Photoshop CS 3, Graphic Converter
5. Subsequent imports don't appear to have the problem.
SUGGESTS:
• A database problem?
RESOLUTION STEPS:
Attempted with no corrective results.
1. Trashed problem photos and emptied iPhoto Trash, reimported images from Ext. HD via drag-n-drop to library index
2. Above, re-imported via File > Import to Library ...
3. Above 1 and 2 import steps with files copied to Local HD
4. Step 3 above with duplicated files (via File > Duplicate)
5. Opened a photo file in Preview, did save as ..., imported into iPhoto
6. Step 5 above with Photoshop CS3, slightly cropped image, saved as, imported into iphoto.
7. Ran "Disk Utility > Verify and Repair Disk" from Snow Leopard Install Disc (there were file and folder count mismatch issues)
8. Re-ran Verify afterwards with clean bill of health.
RECREATION STEPS:
Unknown on how to initially trigger but the last and only iPhoto Console logs appear to be from around the time the issue began:
11/6/09 9:07:39 AM [0x0-0x1e51e5].com.apple.iPhoto[3976] Fri Nov 6 09:07:39 Trebor-4.local iPhoto[3976] <Error>: kCGErrorIllegalArgument: CGSShapeWindow
11/6/09 9:07:39 AM [0x0-0x1e51e5].com.apple.iPhoto[3976] Fri Nov 6 09:07:39 Trebor-4.local iPhoto[3976] <Error>: kCGErrorFailure: Set a breakpoint @ CGErrorBreakpoint() to catch errors as they are logged.
11/6/09 3:05:24 PM ScreenSaverEngine[6784] ILLogger ILMediaBrowserPathWatcher: ** Error in ILMediaBrowserPathWatcher startFSEventStream failed to start for paths: (
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11/6/09 10:18:36 PM [0x0-0x2d62d6].com.apple.iPhoto[6959] Fri Nov 6 22:18:36 Trebor-4.local iPhoto[6959] <Error>: CGImageDestinationAddImageFromSource image 0 of source is nil
11/6/09 10:18:36 PM [0x0-0x2d62d6].com.apple.iPhoto[6959] Fri Nov 6 22:18:36 Trebor-4.local iPhoto[6959] <Error>: CGImageDestinationFinalize image destination does not have enough images
11/6/09 10:25:50 PM iPhoto[345] ILLogger ILMediaBrowserPathWatcher: ** Error in ILMediaBrowserPathWatcher startFSEventStream failed to start for paths: (
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Any thoughts or insights would be appreciated.
Thx
Message edited for typos and format errors by Lyle Turner

RESOLVED (if not altogether answered)
Performed the iPhoto database rebuild cha-cha again - this time selecting ALL checkboxes (previously only selected "Rebuild from backup)
After rebuild, some photos appeared to be fixed, but photos that still showed the the error were all within specific Photo Rolls and DID NOT allow me to "show original file" on right click.
On inspection within the iPhoto Library package, the remaining problem photo files were all ALIASES, not actual image files.
Although the error dialog allowed me to to try and find the missing original, browsing for it didn't work. All image files listed in the browser were grayed out and not selectable.
SO, not sure if this was kosher, but the following seemed to clear things up:
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* copied the real files over the aliases of the same file name
* accepted finders warning that I was replacing files of the same name
* returned to the iPhoto rolls and previewed the previously error prone images
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iPhoto seemed none the wiser, and the error message was gone. (oddly, initially the first photo in each affected roll still threw up the error, but when I moved on the the next one and came back, all seemed well and the message was gone)
Did not appear to be a rhyme or reason to which rolls contained aliases and which didn't - photo/file date stamps weren't contiguous (so it wasn't a problem of a series of event imports from the camera/card.)
Best I can figure is somehow some sets were imported as referenced files although my iPhoto is set to use a managed library.
I'm in the process of consolidating some older manually managed image archives, so I don't know when this happened, or if it's the result of some accidental duplication, aborted import or what. I DO know that I had not encountered this error before, and I know I reviewed the affected rolls some time in the past, long after I had imported them.
Well, all seems to be on the mend. So life is good.
Except for those crufty leftovers. May still want to do something about that.
Thanks to Terence for leading me to look in the right places.
Message was edited by: Lyle Turner

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Can Performance be effect by setting db_file_simultaneous_writes to high

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