Tim can always be counted on as the voice of rationality. Here is the link
I was referencing by the way. There are several discussions on the subject
on asktom, and as I recall Steve Karam ran into an Oracle bug with i/o on
some block sizes a few years ago. I think it has since been fixed:
https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:5942798800346009065
On Thu, Oct 1, 2015 at 11:20 AM, Tim Gorman <tim@xxxxxxxxx> wrote:
Franck's post is great, but doesn't cover some other factors that impact
the decision.
Consider a RAC database with a lot of cross-instance communication.
Cross-instance communication is clearly dependent on how the application
was designed, configured, and deployed. TCP jumbo frames are recommended
for the private interconnect in RAC because it raises the maximum TCP
packet size from the default of 1500 to 9000 (or a little less considering
packet headers). When DB_BLOCK_SIZE is 8192, then clearly MTU=9000 is
optimal.
Now just because the DB_BLOCK_SIZE changed to 16384 or 32768 doesn't mean
that MTU=9000 is not a good thing, just not as good as before.
Is MTU <= 9000 a problem? Increasing MTU size doesn't increase native
network throughput, but it does cut down on the processing by the server to
packet-ize and un-packet-ize, thus it does decrease CPU utilization.
Having DB_BLOCK_SIZE=8192 makes Oracle block slide nicely into TCP packets
with a minimum of effort. Having to packet-ize and un-packet-ize is only a
matter of expending more CPU.
Is CPU utilization a problem? Only if your servers are maxed out for
CPU. If they aren't, then no problem. If they are, then you have a
serious problem.
The upshot is: are you prepared to test all these factors (and others not
mentioned)?
If the answer is yes, then have at it, and good luck.
If you're just looking for easy optimizations, then this isn't it. There
are far more effective optimizations to consider.
My US$0.02...
On 10/1/15 10:02, Stefan Koehler wrote:
Hi Orlando,--
it depends (as always).
Franck Pachot has written a great blog post with several demos about this
topic: http://blog.dbi-services.com/do-the-block-size-matter/
Best Regards
Stefan Koehler
Freelance Oracle performance consultant and researcher
Homepage: http://www.soocs.de
Twitter: @OracleSK
Orlando L <oralrnr@xxxxxxxxx> hat am 30. September 2015 um 23:29--
geschrieben:
List,
Does anyone in the list use non default blocksize of greater than
8K for your oracle DBs; if so, is it for warehousing/OLAP type applications?
What advantages do you get with them; any disadvantage.
Orlando.
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