Oracle Cache Fusion Internal
Oracle Cache fusion, private inter connects and
practical performance management considerations in
Oracle RAC
In the article you will have a look at the cache fusion from the perspective
of the Practical Performance Management for Oracle RAC. Cache fusion is based
and heavily depends on Private Interconnect. The article will emphasize on
the Interconnects impact, often overlooked and underestimated, on the RAC
performance. Tuning RAC is similar to tuning of a regular single instance
database and in addition takes into account the overhead of the interconnects
existing in Oracle RAC (10gR1/10gR2/11gR1/11gR2). Some well known cases will
be addressed in RAC to improve performance.
In this article you will review the Oracle fundamentals and infrastructure
architecture and you will look at the Cache Fusion impact on the RAC
performance. The outlined in the article guidelines has two objectives:
Maximize the utilization of the software and hardware for Private
Interconnect. Make sure that you fully utilize the maximum of your
capacity. Increase the bandwidth, throughput and decrease latency. You
will look at considerations for the Private Interconnect.
o network Architecture
o network configuration
o network settings
o TCP/UDP configuration and settings
o OS settings
Minimizing Cache fusion traffic across the private interconnects. Look
at how to diagnose, determine and resolve problems related to Cache
fusion addressing some common problems, derived from the cache fusion
wait event and statistics, known to exist in Oracle RAC.
RAC Fundamentals and architecture
Oracle RAC is a parallel database architecture aiming at high availability
and parallelism in a grid deployment. Concept of a grid is based on providing
and distributing computing resources on demand. Oracle RAC is shared disk
architecture. Oracle RDB database is another example of shared disk
architecture. An alternative to Shared Disk Architecture is Shared nothing
architecture. Shared nothing architecture is parallel database architecture
(Teradata, IBM DB2, and Informix) based on MPP (Massive Parallel processing.
The table below represents RAC architecture and all layered components
(RDBMS, clusterware resources, Oracle clusterware etc...)depends on the
private interconnect.
Note 1
Node N
Oracle RDBMS
Oracle RDBMS
Oracle Clusterware resources (VIP,
Oracle Clusterware resources (VIP,
SCAN, Listeners, ASM etc…)
SCAN, Listeners, ASM etc…)
Oracle clusterware/GI
Oracle clusterware/GI
Private network (same subnet, same
interface names across all nodes)
Private network (same subnet, same
interface names across all nodes)
Public network (same subnet, same
interfaces across all nodes)
Public network (same subnet, same
interfaces across all nodes)
Same OS (Oracle Supported)
Same OS (Oracle Supported)
Shared or Cluster file system for the shared storage (Oracle supported)
GPFS, Veritas, ASM, etc...
Shared disk hardware storage (Oracle supported)
Function and processes for CGS, GES and GRD
SGA for a RAC database includes some new structures as show below in
the image.
RAC Database System has two important services. They are Global Cache Service
(GCS) and Global Enqueue Service (GES). These are basically collections of
background processes and memory structures. These two services GCS and GES
together manage the total Cache Fusion process, resource transfers, and
resource acquisition among the instances. Major processes are:
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