||Oracle Tips by Burleson
Oracle10g Grid Computing
Chapter 12 - RAC Design Considerations
Proper Sequence Usage
not used properly, sequences can be a major headache in RAC. Generally
speaking, sequences should be either CACHED or ORDERED, but not both.
The preferred sequence is a CACHED, non-ordered sequence. If the
ordering of sequences is forced, performance in a RAC environment will
suffer unless ordering the sequence to a single node in the RAC
cluster isolates insert activity.
Another method to optimize the use of sequences is to use a staggered
sequence insert trigger. A staggered sequence insert trigger is a
specific constant added to the sequence value based on the instance
number. This isolates each set of inserts and prevents inadvertent
attempts to use the same sequence number. An example of a staggered
sequence insert trigger is shown in Figure 13.5. A staggered sequence
trigger will insert the values into indexes such that each instance’s
values are staggered to prevent index node intra-node transfers. The
formula to allow this is:
index key = (instance_number -1)* 100000+ Sequence number
CREATE TRIGGER insert_EMP_PK
BEFORE insert ON EMP
FOR EACH ROW
For more information,
see the book
Grid and Real Application Clusters 30% off if you
buy it directly from Rampant TechPress .
Written by top Oracle
experts, this RAC book has a complete online code depot with
ready to use RAC scripts.
can offer world-class remote Oracle database support at super-affordable prices.
Oracle DBA service provides 100% of the remote Oracle database administration
needs for your company, and includes 24x7 access to our staff of 100% OCP
Certified Oracle DBAs.
We require a 12 month service commitment and include the following services:
- Initial configuration review and problem identification
- Installation of Oracle statistics collection mechanisms and quarterly
database growth summaries
- Hourly monitoring of your Oracle database for pending problems
- Periodic performance analysis & identification of tuning activities
- Twenty Four hour Oracle emergency support
- Reporting and resolving all serious Oracle alert log messages
- Free use of the BC
- Quick response emergency support for production database outages
- Four hours of free remote DBA support every month. You can use these free
hours for any DBA activity, including database analysis, system design,
production migrations or personal mentoring.
information, please visit www.oracle-training.cc.