Re: Parallel server and degree of parallelism ..

From: Rajesh Bhave >>
Can someone give small example as to when parallel server can be useful and what is degree of parallelism ? <<

Degree of parallelism refers to parallel query while parallel server refers to the Oracle Parallel Server, OPS, and this is a totally different topic.

The degree of parallelism is basically the number of concurrent processes that will be started to handle the data retrieval portion of the query. If you had a table that had extents in four separate data files on four disk then you could set the degree of parallelism to four so four full table scans would run at one time. It a sort was necessary you could also have four sort processes started at the same time. One process would manage the query so you could have nine processes running to support one SQL, with a defree of only four. There are numerous factors and parameters which control how many processes you actually get.

OPS is the sharing of one physical database amount multiple instances of Oracle, each of which is on a separate machine. If you have a machine that can not be expanded you can add a another node to handle a growing load or the second instance could be a hot spare should the first machine fail. Some Unix vendors support automatic failover from one box to another.

It is possible to parallelize a query across instances with OPS.

I hope this helps.

Mark Powell -- Oracle 7 Certified DBA
- The only advice that counts is the advice that you follow so follow your own advice - Received on Thu Nov 19 1998 - 18:10:50 CST