Re: i know cary millsap is super smart but...
- From: Dba DBA <oracledbaquestions@xxxxxxxxx>
- To: ORACLE-L <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 29 Aug 2013 11:33:18 -0400
This is probably not directly related to this question, but its close. On
my previous project we migrated from HP-UX where I believe we had 16 CPU
servers in development/test. We supported multiple DBs on these servers. We
went to IBM AIX, where we had 2, quad core CPUs (so 8 virtual CPUs),
however, each DB was on a separate server.
This worked without issue except when we had to do bulk changes that
involved 'parallel sql'. I had a bulk update that used parallel 4 for both
reads and the update. This seemed to cause a race condition on the CPU.
When we looked at the events, 99.9% of the events where parallel waits. I
take these to be messages piped to and from the query controller to tell
the slave sessions what to do. When I checked the number of sessions
created, it was a total of 8 plus 1 query controller. I know you can
sometimes get 2x the number of sessions for each parallel level (this was
debated on here back in 2007/2008).
Now I know that the other servers had a lot more CPUs, but they had many
DBs running on them that were very active. So it is not like we were using
alot of parallel and nothing else was running on these servers. Some of us
started looking into the AIX docs and it appeared that the architecture of
their CPUs/backend were considerably different than the HP-UX architecture.
This was never going to be an issue in production. I cannot remember how
many CPUs we had in production, but it was much larger and we did not have
issues with using parallel. This actually made doing builds/maintenance
more of a hassle because we had to lower down our parallel level. The
initial hope had been that if we put each DB on a different server, we
would be more efficient, because there are times when some dev/test
environments were hit harder than others and this was leading to
performance issues in other DBs on the same server.
I think there may be more to it than the number of CPUs/virtual CPUs. There
may be architecture differences between systems. That being said, I am NOT
a hardware expert. Is anyone on here familiar with IBM Server architecture?
I do not know the exact server we bought. I don't work there anymore so I
can't check.
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