Re: Question on Parallel ORACLE on NCR 3600
Date: 26 Jul 94 11:50:10 GMT
Message-ID: <262_at_ncrsecp.Copenhagen.NCR.COM>
>In article <311dre$t65_at_crl.crl.com> Carolyn Binder writes:
>Parallel Oracle Scenario (loosely coupled):
>Assume there are two processors on an SMP, sharing an Oracle database.
^^^
I take it that you mean that we assume to have two SMP's (with any number of
CPU's) loosely coupled in what genericly is known as an ORACLE cluster.
>If one requests a block of information that the other one has in memory,
>how will the data be obtained? I figured that the requesting process
>would end up getting the info from the memory of the other, rather than
>doing disk i/o, which'd be slower.
As the ORACLE Parallel Server is designed, there is no other option than to write the block to disk and read it into memory of the requesting node. This is slower than just shuffling data across a network to the requesting instance. However, this will only occur if the data has been modified by the first instance to read the block into memory. If the block has not been modified, the requesting instane will read the block from disk without requiring the first instance to write the block. This is a function of the ORACLE Parallel Server and is true for all hardware platforms that it runs on.
A large part of the design of an ORACLE Parallel Database concentrates on minimizing the possibility that two instances modifies the same datablocks at the same time.
>
>The real reason I'm asking this is because I'm trying to understand how
>parallel Oracle works on an NCR 3600 box we're looking at. We want to
>reduce intraprocessor communication between APs because the Ynet is slower
>than an AP's internal bus. The reps are telling me that very little
>communication goes across the Ynet, and *no* database data travels on the
>Ynet. So in the case above, how do the processors exchange data? Far as
>I know, the YNET is what connects the two Aps; I think I'm missing something.
>
Well, the sales rep's are telling you the truth !
The 3600 is made up of a number SMP's connected both by the YNET and ethernet. The database is stored on disks, accessible from all the instances via a shared SCSI. Since the ORACLE Parallel server restricts data exhange between instances to writing and reading from disks the only information that travels across the YNET is information about which blocks have been read into memory and whether the block is going to be modified or not. Since the 3600 is "born" with the YNET connection and the YNET is a lot faster than e.g. ethernet this is the preferred connection. Other hardware platforms use other network connections for the same functions.
Hope this helps a little.
Jorgen Quaade
AT&T Global Information Solutions
Systems Engineering Copenhagen
Svanevej 14
DK-2400 Copenhagen NV
Denmark
Phone, Switchboard: +45 38 15 75 00 Phone, Direct: +45 38 15 75 85 FAX: +45 31 10 23 62 Email: Jorgen.Quaade_at_Copenhagen.ncr.comReceived on Tue Jul 26 1994 - 13:50:10 CEST