Re: How about just open one node of RAC in read-write mode, others in read-only mode?

On Tue, 06 Dec 2005 04:26:28 -0800, AnySQL (d.c.b.a) wrote:

> RAC is still not good at multi-node write model, how about just open
> one node in read-write mode, keeping other nodes in read-only mode, is
> it possible? I just want to force a one-write-multi-read model.
> thanks.

When you open the database, you will write that fact into the control file, even if you open the database in read-only mode. Control file is a global resource, used by all instances. Most likely, you cannot have that. You can, however, have an instance and a logical standby which would be open for reading.

Second, RAC is good in the multi-node write model, as long as you abide by locking rules and committing rules. Application which does "select for update" and then allows the operator to decide whether to commit or take a lunch break, with rows firmly locked, is likely to cause slight discomfort to its users. Also, you shouldn't be saving money on hardware. Hardware cost of real multiuser RAC is at least $500,000. If you save money on the machines, then you have to buy fast disks with lots of non-volatile RAM and smart software (EMC, for short). For RAC system, you need throughput: you need to guarantee that the configuration is able to perform certain number of I/O requests per second. Typical numbers are around 3000-5000. Without that, you are saving money on the wrong side. Either, RAC isn't for you or you bought a non-functional toy. You should have called GEICO and saved some money on car insurance if you are into saving money. RAC is expensive. Always has been and it will remain so in the near future. The key to RAC purchase are references. You should always ask for another customer, in the same or similar industry as you are, who purchased RAC. Then call them and ask them how are they satisfied, what are they doing, what is average response time for the interactive applications, the size of database and the number of concurrent transactions. If the vendor is unwilling to provide such references, run like hell. Last thing about RAC is its purpose: RAC is not a performance option in an OLTP world. RAC is a survivability option. Two SUN E450 boxes clustered over A1000 disk array will not give you any performance benefit over a single one. As a matter of fact, decently configured Dell box with RH EL 4.0 will beat the crap out of the much more expensive dual SUN configuration above. If you want OLTP speed and RAC, then we are talking real money and real machines.

-- 
http://www.mgogala.com