Cary, I tend to agree with you when analyzing a given problem, but a first
glance or the first indication is often an excessive amount of I/O (logical,
physical - or both). And when we hit the jackpot it's usually in the 2
points covering the 80% (shitty sequel and no-brain 3GL).
Mladen, you're also right. It really IS so much more fun to guess. And the
more experience we have in analyzing the better we are at guessing - and we
even have more fun as it goes (well... maybe not always..) .... ;)) -
unfortunately is doesn't solve all the problems.....
In my humble experience I've started to see problems more frequently on the
O/S side - in particular in the choice of filesystems and/or configurations.
One example being Veritas Cluster Filesystem used by RAC. RAC is not the
problem (ehh.... almost not), but VCFS is, despite their own description:
Near Rawdevice Speed! - not quite true in my humble experience.
The filesystems are owned by a single coordinating process on one of the
participating nodes, which makes the full I/O rate dependent of how freaking
fast this single process can handle UDP sync packages accross the
interconnect. So when the system tops the speed, the average node (having 6
cpu's) is utilized ~60%, when I/O requests are rather small on average (~64K
accross all nodes with the majority at 16K) - giving a total throughput of
~650MB/sec for all nodes (not each node - but ALL together).
During backup and batch where I/O request size tops at 512KB, the I/O rate
increases to ~800-900MB/sec.
Monitoring the system shows that I/O tops when the VCFS coordinator takes
+90% of one cpu.
The theoretical I/O limit for this RAC system is the capacity of 12 2Gbit
Fiber HBA's, ie. ~2GB/s.
In this case I totally agree with Cary that I/O is not the real issue and I
had a lot of analysis in finding out the true cause. Guessing gave a good
head start - but without the experience guessing is random instead of being
"qualified guessing".
Just my 2c...
/Stig
----Original Message Follows---- From: Steve Perry <sperry@xxxxxxxxxxx> Reply-To: sperry@xxxxxxxxxxx To: cary.millsap@xxxxxxxxxx CC: "Mladen Gogala" <gogala@xxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx> Subject: Re: full-scan vs index for "small" tables Date: Tue, 27 Jun 2006 21:46:52 -0500
On Jun 27, 2006, at 09:52 AM, Cary Millsap wrote:
What have been the majority of problems you've run into?
I'm curious what others have run into.
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