Oracle Cache Fusion Internal

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2019-08-22

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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 Clusterware resources (VIP,

SCAN, Listeners, ASM etc…)

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)

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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