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Thread: Rac Architecture

  1. #1
    Oracle Administrator
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    Feb 2012
    New Delhi, India

    Rac Architecture

    A cluster is a set of 2 or more machines (nodes) that share or coordinate resources to perform
    the same task.
    A RAC database is 2 or more instances running on a set of clustered nodes, with all instances
    accessing a shared set of database files.
    Depending on the O/S platform, a RAC database may be deployed on a cluster that uses vendor clusterware plus Oracle's own clusterware (Cluster Ready Services), or on a cluster that solely uses Oracle's own clusterware.
    Thus, every RAC sits on a cluster that is running Cluster Ready Services. srvctl is the primary tool DBAs use to configure CRS for their RAC database and processes.

    Cluster Ready Services and the OCR

    Cluster Ready Services, or CRS, is a new feature for 10g RAC. Essentially, it is Oracle's own clusterware. On most platforms, Oracle supports vendor clusterware; in these cases, CRS interoperates with the vendor clusterware, providing high availability support and service and workload management. On Linux and Windows clusters, CRS serves as the sole clusterware. In all cases, CRS provides a standard cluster interface that is consistent across all platforms.

    CRS consists of four processes (crsd, occsd, evmd, and evmlogger) and two disks: the Oracle Cluster Registry (OCR), and the voting disk.

    CRS manages the following resources:

    The ASM instances on each node
    The instances on each node
    Oracle Services on each node
    The cluster nodes themselves, including the following processes, or "nodeapps":
    The listener
    The ONS daemon
    CRS stores information about these resources in the OCR. If the information in the OCR for one
    of these resources becomes damaged or inconsistent, then CRS is no longer able to manage that resource. Fortunately, the OCR automatically backs itself up regularly and frequently
    Interacting with CRS and the OCR: srvctl

    srvctl is the tool Oracle recommends that DBAs use to interact with CRS and the cluster registry.
    Oracle does provide several tools to interface with the cluster registry and CRS more directly,
    at a lower level, but these tools are deliberately undocumented and intended only for use by Oracle Support. srvctl, in contrast, is well documented and easy to use. Using other tools to modify
    the OCR or manage CRS without the assistance of Oracle Support runs the risk of damaging the OCR.

    Oracle10g RAC Service Architecture

    Overview of Real Application Cluster Ready Services, Nodeapps, and User Defined Services

    Service Architecture
    Cluster Ready Services (CRS)
    ASM Servodeapps
    User defined Services ices
    Internally Managed Services
    Monitoring Services

    RAC Service Architecture

    Oracle 10g RAC features a service based architecture
    This is an improvement over 9i RAC in several ways
    Increased flexibility
    Increased manageability
    Improvements in High Availability
    Enables 10g Grid Deployment

    RAC Services and High Availability

    Oracle Services facilitate high availability of databases and related applications
    If key database resources become unavailable (network, storage, etc.):
    Instances and Services will be relocated to another node
    The “failed” node will be rebooted
    By default, after any server boot-up, Oracle attempts to restart all services on the node

    Cluster Ready Services

    Manage the RAC Cluster
    Several Different Services
    Oracle CSService
    Required for RAC installation
    Installed in its own CRS_HOME

    CRS Basics

    Used to manage RAC
    Only one set of CRS Daemons per system
    Multiple instances share the same CRS
    CRS runs as both root and Oracle users
    CRS must be running before RAC can start

    CRS Management

    Started automatically
    Can stop and start manually
    Start the OracleCRSService
    Stop the OracleCRSService
    Uses the voting disk and OCR (Oracle Cluster Repository)
    Requires 3 network addresses
    Virtual Public

    CRS Services

    Cluster Ready Services Daemon
    Oracle Cluster Synchronization Service Daemon
    Event Manager Daemon
    Process Monitor
    Cluster Ready Services Daemon


    Runs as Administrator user
    Automatically restarted
    Manages Application Resources
    Starts, stops and fails-over application resources
    Maintains the OCR (Oracle Cluster Repository)
    Keeps state information in the OCR

    Oracle Cluster Synchronization Service Daemon

    Runs as Administrator user
    Maintains the heartbeat (failure causes system reboot)
    Provides Node Membership
    Group Access
    Basic Cluster Locking
    Can integrate with 3rd party clustering products or run standalone
    OracleCSService also works with non-RAC systems

    Event Manager Daemon

    Runs as Administrator user
    Restarts on failure
    Generates Events
    Starts the racgevt thread to invokes Server Callouts

    Process Monitor

    Runs as Administrator user
    Locked in memory to monitor the cluster
    Provides I/O fencing
    OraFenceService periodically monitors cluster status, and can reboot the node if a
    problem is detected An OraFenceService failure results in
    Oracle Clusterware restarting the node


    RACG is a behind-the-scenes process (or thread) that extends clusterware to
    support Oracle-specific requirements and complex resources.
    Runs server callout scripts when FAN events occur.
    Runs as processes (or threads), not as a service (racgmain.exe, racgimon.exe)

    Cluster Ready Services Management

    Log Files
    Oracle Cluster Registry (OCR)

    Nodeapp Services

    Nodeapps are a standard set of Oracle application services that are automatically
    launched for RAC
    Virtual IP (VIP)
    Oracle Net Listener
    Global Services Daemon (GSD)
    Oracle Notification Service (ONS)
    Nodeapp services run on each node
    Can be relocated to other nodes through the virtual IP

    VIP (Virtual IP)

    Creates a virtual IP address used by the Listener
    The virtual IP address fails over between nodes
    Multiple virtual IP addresses can exist on the same system (during failover)
    Independent of the Oracle Instance
    Potential Problem if more than one database per node

    Global Services Daemon (GSD)

    The daemon which executes SRVCTL commands
    GSD receives requests from SRVCTL to execute administrative tasks, such as startup or shutdown
    The command is executed locally on each node, and the results are sent back to SRVCTL.
    The daemon is installed on the nodes by default. It is important that you do not kill this process and it should not be deleted.


    Server-side component of Oracle Net
    Listens for incoming client connection requests
    Manages the traffic to the server; when a client requests a network session with a server,
    the listener actually receives the request and brokers the client request
    If the client's information matches the listener's information, then the listener grants
    a connection to the server.

    Oracle Notification Service (ONS)

    The Oracle Notification Service is installed automatically on each RAC node as a
    Node Application
    ONS starts automatically with each boot
    ONS uses a simple push/subscribe method to publish event messages to all RAC
    nodes with active ONS daemons

    ONS and Fast Application Notification

    ONS can be configured to run on nodes hosting client or mid-tier applications
    ONS is the key component of Fast Application Notification (FAN)
    Can be utilized to extend RAC high availability and load balancing to mid-tier
    Independent of True Application Failover
    Less reliance on network configuration

    User Defined Services

    User defined, named services may be created to manage database resources that are associated with application workloads
    One or more database instances may be mapped to a single service
    A database instance may be assigned to one or more services
    The Automated Workload Repository may be used to monitor Service metrics

    User Defined Services and Failover

    Services can be defined with preferred and alternate instances
    A service may be assigned to start on preferred instances
    The same service may have alternate instances assigned for failover
    If multiple services are assigned for the same database, the preferred and alternate instance assignments may be different for each service

    Automatic Storage Management Services

    Automatic Storage Management (ASM) is a storage option for creating and managing databases
    ASM operates like a Logical Volume Manager between the physical storage and the database.
    A small, automatically managed Oracle database instance is created on each node (if ASM is chosen
    as a storage option)
    ASM instances start automatically as Oracle services

    Internally Managed Services

    When the Global Services Daemon is started as a part of the Node Applications,
    it in turn launches key internally managed services
    The Global Cache Service manages Cache Fusion and in-memory data buffers
    The Global Enqueue Service manages inter-instance locking and RAC recovery
    GCS and GES show up as OS processes or threads,
    but GSD is the only service that can be externally controlled
    GCS and GES together manage a set of virtual tables in memory,
    called the Global Resouce Directory
    Global Cache Service (GCS)

    The controlling process that implements Cache Fusion.
    Manages the status and transfer of data blocks across the buffer caches of all instances.
    Tightly integrated with the buffer cache manager to enable fast lookup of resource
    information in the Global Resource Directory.
    Maintains the block mode for blocks in the global role.
    Employs various background processes (or threads) such as the
    Global Cache Service Processes (LMSn) and Global Enqueue Service Daemon (LMD).

    Global Enqueue Service Monitor (LMON)

    Background process that monitors the entire cluster to manage global resources.
    Manages instance and process expirations and recovery for GCS.
    Handles the part of recovery associated with global resources

    Global Resource Directory

    The data structures associated with global resources. It is distributed across all
    instances in a cluster.
    Global Cache Service and Global Enqueue Service maintain the Global Resource
    Directory to record information about resources and enqueues held globally.
    The Global Resource Directory resides in memory and is distributed throughout the
    cluster to all nodes. In this distributed architecture, each node participates in
    managing global resources and manages a portion of the Global Resource Directory.

    Monitoring RAC Services



    Monitoring RAC Services

    Creating a tabular report:
    %ORA_CRS_HOME%\bin\crs_stat -t
    Name Type Target State Host


    ora.rac1.gsd application ONLINE ONLINE rac1

    ora.rac1.oem application ONLINE ONLINE rac1

    ora.rac1.ons application ONLINE ONLINE rac1 application ONLINE ONLINE rac1

    ora.rac2.gsd application ONLINE ONLINE rac2

    ora.rac2.oem application ONLINE ONLINE rac2

    ora.rac2.ons application ONLINE ONLINE rac2 application ONLINE ONLINE rac2


    What advantages does a service based architecture offer?
    What four services comprise Cluster Ready Services?
    Nodeapps consists of which four applications?
    True or False: a database instance may be assigned to multiple services


    Service Architecture
    Cluster Ready Services (CRS)
    User defined Services
    ASM Services
    Internally managed services
    Global Cache Service
    Global Enqueue Service
    Global Resource Directory
    Monitoring Services
    Last edited by devesh_ocp; 04-25-2012 at 12:05 PM.

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