Oracle RAC. Introduction to Oracle RAC.

Oracle RAC. Introduction to Oracle RAC.
Nov 29, 2019.

Overview of Oracle RAC
A cluster comprises multiple interconnected computers or servers that appear as if they are one server to end users and applications.
Oracle RAC enables you to cluster an Oracle database. Oracle RAC uses Oracle Clusterware for the infrastructure to bind multiple
servers so they operate as a single system.

Oracle Clusterware is a portable cluster management solution that is integrated with Oracle Database. Oracle Clusterware is also a required
component for using Oracle RAC. In addition, Oracle Clusterware enables both noncluster Oracle databases and Oracle RAC databases
to use the Oracle high-availability infrastructure. Oracle Clusterware enables you to create a clustered pool of storage to be used
by any combination of noncluster and Oracle RAC databases.

Oracle Clusterware is the only clusterware that you need for most platforms on which Oracle RAC operates.
You can also use clusterware from other vendors if the clusterware is certified for Oracle RAC.

A cluster consists of multiple interconnected servers that appear to end users and applications as if they are one single server.

Typical Oracle RAC Architecture.

Oracle RAC databases differ architecturally from noncluster Oracle databases in that each Oracle RAC database instance also has:
At least one additional thread of redo for each instance.
An instance-specific undo tablespace.
The combined processing power of the multiple servers can provide greater throughput and Oracle RAC scalability than is available from a single server.

Simply put Real Application Cluser (RAC) is,
Multiple instances accessing the same database

One instance per node
Physical or logical access to each database file
Software-controlled data access.

Clusteware is software which will bind all the Nodes in a single system.

How the RAC software changed from version to version.
Oracle RAC Software.

9i                       Cluster manager
10gR1                  CRS S/W
10gR2                 Clusterware
11gR1                   Clusterware
11gR2                  Grid Infrastructure Services
12cR1                  Grid Infrastructure Services
12cR2                 Grid Infrastructure Services

Criteria for RAC deployment..

* Oracle defines the database as being the structures that reside in files permanently on disk,including the datafiles,the controlfiles  and online redologs.
* In the case of RAC  cluster ,the database must be located on shared physical disk storage that all servers in the cluster must be able to access equally.
* The servers communicate with the shared storage via a storage network.
* The servers in the cluster are bound together using cluster management software called Oracle Clusterware/Grid Infrastructure Services.
* This enables the servers to appear as though they are single server. Servers in the cluster communicate
   with each other using a dedicated private network known as the Cluster Interconnect.
* Each server is also connected to a public network that allows the cluster to communicate with the  outside world,including clients and application servers.
* In RAC cluster ,each instance can execute transactions concurrently because access is coordinated to ensure data consistency and integrity.
* Instances exchange messages  with each other across the interconnect to manage the state of individual Oracle data blocks and locks.

RAC Installation Notes.
* At the time installation , we need to select on which nodes we have to install Grid setup . Only one note needs the Grid Setup. Node 1.
* , will be executes manually on all the nodes.
* we have to set oratab and initab in all the nodes
* All the nodes have to access the shared storage to get the data from physical datafiles.
* ./runInstaller need to be run on only one node.

Benefits of Real Application Cluster.
* Lower Overall Cost of Ownership
* Expanded Scalability
* High Availability
* Buffer Cache Management
* Row Locking
* Recovery Manager, Online Backups, and Archiving.

Archivelog Notes.
* In Real Application Clusters, each instance automatically archives its own redo log files, or one or more instances can archive
   the redo log files for some or all of the instances in the cluster database.
* If you operate your database in NOARCHIVELOG mode, then you can only make offline backups. If you cannot afford data loss,
   then Oracle strongly recommends that you use ARCHIVELOG mode.


Oracle Exadata. Current Exadata Machine 19.1.0. Features and capabilities.

Oracle Exadata. Current Exadata Machine 19.1.0. Features and capabilities.
Nov 25, 2019.

1. OS. Oracle Linux 7.5
The Oracle Linux kernel UEK4 that has been used in previous releases continues to stay the same.

2. Oracle Database Software Minimum Required Version.
The following Oracle Database and Oracle Grid Infrastructure software releases are supported with Oracle
Exadata System Software release 19.1.0 and Oracle Linux 7.5.

* Oracle Database and Oracle Grid Infrastructure 19c
* Oracle Database and Oracle Grid Infrastructure 18c
   Minimum version
* Oracle Database and Oracle Grid Infrastructure 12c Release 2 (
   Minimum version
* Oracle Database and Oracle Grid Infrastructure 12c Release 1 (
   Minimum version
* Oracle Database 11g Release 2 (
   Minimum version
   Requires Oracle Grid Infrastructure release or higher
* Oracle Database 11g Release 2 (
   Minimum version
   Requires Oracle Grid Infrastructure release or higher
   Installation of the Oracle Database software is a manual task for this release and is not covered by OEDA.

3. Automated Performance Monitoring.
Oracle Exadata System Software can automatically detect performance issues and figure out the root cause without
human intervention. Examples of how this feature operates include:

* If a spinning process is taking up all the resources on the system and impacting database performance, Oracle Exadata
   System Software automatically detects the CPU spin, pinpoints the exact process that is causing the spin, and generates an alert.

* If the Oracle database is not properly configured with huge pages according to the best practice recommendation, Oracle Exadata
   System Software automatically detects the misconfiguration and generates an alert for the affected database instances.
   There is no configuration required for this feature. To receive alerts, you must configure the notification mechanism. See Monitoring
   Requests and Alerts for Oracle Exadata Storage Server and ALTER DBSERVER.

As a part of this feature, Management Server (MS) is enabled on user domains (domU) in addition to storage servers,
database servers (bare metal configuration), and management domains (dom0).

Minimum requirements:
Oracle Exadata System Software 19.1.0 

4. Faster Smart Scans Using Column-Level Checksum.
Checksum computation and validation helps to detect errors that may happen during storage or retrieval of data.
A checksum is computed when a piece of data is written to Exadata Flash Cache and the checksum is verified on a subsequent read.

The key benefits of the column level checksum approach are:
* Selective checksum computation: When smart scan reads a flash block containing the columns of interest, checksum verification is performed
   only for those specific column   CUs even though there are many other columns present in the cache line. This reduces the amount of data on
   which the checksum is performed resulting in lower CPU usage. For example, consider the predicate A < 5 and Z < 10. The flash block where
   column A resides could contain columns B, C, and D. However, because B, C, and D are not referenced in the query, checksums are not performed for B, C, and D.

* Just in time checksum computation: Checksums are performed only when a column is processed. For example, consider the predicate A < 5 and Z < 10.
   Checksum is computed on the column CU for column A and the predicates are evaluated. If there are no rows satisfying the predicate A < 5, then there is
   no reason to evaluate Z < 10. Checksum computation is not performed on the column CU for column Z. This can greatly reduce the amount of data on which
   the checksum is performed resulting in lower CPU usage.

This feature is automatically enabled when you configure the INMEMORY_SIZE database initialization parameter and upgrade to Oracle Exadata System
Software release 19.1.0; no further configuration is required to use this new feature.

Minimum requirements:

* Oracle Exadata System Software release 19.1.0
* Exadata Smart Flash Cache
* INMEMORY_SIZE database initialization parameter

5. Enhanced OLTP High Availability During Cell Outages and Flash Failures.
If a cell goes offline or a flash device fails, then the databases redirect IOs to use secondary mirrors for data read operations because
the primary mirrors are unavailable due to the outage. However, the secondary mirrors might not be in the flash cache of the respective cell,
so the databases must read the data from hard disks. This can negatively impact application performance due to flash cache misses.

With this new feature, Oracle Exadata System Software prefetches the secondary mirrors of the OLTP data that is most frequently accessed into
the flash cache. This prefetching is done as a background task. Oracle Exadata System Software automatically manages the secondary mirrors in the flash
cache in an optimal way so that newer or more active secondary mirrors replace the cold data in the cache. In addition, when a flash device is replaced, this
feature also ensures that the newly replaced flash device is made more current (warmed up) before redirecting database read operations to the new flash device.
Thus, this feature provides better high availability for application performance by greatly reducing the secondary mirror flash cache misses during cell or flash
device failures and flash device replacements.

This feature is useful for OLTP workloads only. Oracle Exadata System Software does not cache the secondary mirrors for scan data.
Also, this feature is only enabled for write-back Flash Cache. No secondary mirror caching is done for write-through Flash Cache.

Minimum requirements:

* Oracle Exadata System Software release 19.1.0
* Oracle Database 19c
* Exadata Write Back Flash Cache on High Capacity storage servers
* Exadata Database Machine X6 or later (due to flash cache size requirements)

6. Support for Host and Integrated Lights Out Manager (ILOM) on Seperate Network.
This feature helps improve security by enabling you to configure a separate network for ILOM so that the Exadata servers and ILOM are
completely separate from each other.

Minimum requirements.
* Oracle Exadata System Software release 19.1.0

7. DB_UNIQUE_NAME support for Multiple Clusters Sharing Exadata Storage.
You can now use the same DB_UNIQUE_NAME value for databases that share the same storage. This feature enables Oracle Multitenant
clustered databases sharing the same storage cells to have the same DB_UNIQUE_NAME.

This feature eliminates the need for different clusters that share Exadata storage to coordinate the DB_UNIQUE_NAME assignments to avoid a name conflict.
Each cluster is free to choose any DB_UNIQUE_NAME value, without having to coordinate with other clusters, as long as ASM-scoped security is configured
for each cluster.

When ASM-scoped security is configured, the ASM cluster name is used to qualify the DB_UNIQUE_NAME for access to the storage servers.
The metrics and stats collected for each database also use the asmcluster.database name qualification in various areas including I/O Resource
Management (IORM), Flash Cache, and cell offloading.

** Note. There are limitations for Oracle Zero Data Loss Recovery Appliance.

Minimum requirements.
* Oracle Exadata System Software release 19.1.0
* Each database with the same DB_UNIQUE_NAME must be in a different Oracle ASM cluster
* ASM-scoped security configured for each Oracle ASM cluster

8. Secure Eraser Updates.
With Oracle Exadata System Software release 19.1.0, various improvements were made to Secure Eraser.
* Automatic Upgrading of Multi-pass Disk Erasure to Secure Eraser
* Automatic Secure Eraser as Part of Imaging
* Secure Eraser Improvements and New Features

Minimum requirements.
* Oracle Exadata System Software 19.1.0
* Oracle Exadata Database Machine X5-2 or later

9. Server Time Synchronization Uses Chrony.
Minimum requirements:
* Oracle Exadata System Software release 19.1.0

10. Security Improvements.
With Oracle Exadata System Software release 19.1.0, various security improvements were introduced.
* Access Control for RESTful Service
* Advanced Intrusion Detection Environment (AIDE)
* Password Expiration for Remote Users
* Implementing the Principle of Least Privilege to Improve Security
* Increased Security for Storage Server Processes
* SSHD ClientAliveInterval Changed to 600 Seconds
* Stronger Password Requirements
* Upload DIAGPACK to Oracle ASR Manager using HTTPs