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Oracle9i Real Application Clusters Deployment and Performance
Release 2 (9.2)

Part Number A96598-01
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Glossary

buffer busy global cache

A wait event that is signaled when a process has to wait for a block to become available because another process is obtaining a resource for this block.

buffer busy waits

A wait event that is signaled when a process cannot get a buffer because another process is using the buffer at that moment.

cache convert waits

A statistic showing the total number of waits for all up-convert operations, such as global cache null to S, global cache null to X, and global cache S to X.

Cache Fusion

A diskless cache coherency mechanism in Real Application Clusters that provides copies of blocks directly from a holding instance's memory cache to a requesting instance's memory cache.

cache open waits

A statistic showing the total number of waits for global cache open S and global cache open X.

cluster

A set of instances that cooperates to perform the same task.

cluster database

The generic term for an Oracle Real Application Clusters database.

clustered database

See cluster database.

clustering

See cluster database.

Cluster Manager (CM)

An operating system-dependent component that discovers and tracks the membership state of each node by providing a common view of membership across the cluster. The CM also monitors process health, specifically the health of the database instance. The Global Enqueue Service Monitor (LMON), a background process that monitors the health of the Global Cache Service (GCS), registers and de-registers from the CM.

connection load balancing

A feature that balances the number of active connections among various instances and shared server dispatchers for the same service.

connect-time failover

A client connect request is forwarded to another listener if the first listener is not responding. Connect-time failover is enabled by service registration, because the listener knows whether an instance is up prior to attempting a connection.

consistent gets

Consistent gets is a statistic showing the number of buffers that are obtained in consistent read (CR) mode.

consistent read (CR)

The Global Cache Service (GCS) ensures that a consistent read block (also known as the master copy data block) is maintained. The consistent read block is the master block version that records information about all changes to a block. It is held in at least one System Global Area (SGA) in the cluster if the block is to be changed. If an instance needs to read the block, then the current version of the block may reside in many buffer caches as a shared resource. Thus, the most recent copy of the block in all System Global Areas contains all changes made to that block by all instances, regardless of whether any transactions on those instances have committed.

Console

The Oracle Enterprise Manager Console gives you a central point of control for the Oracle environment through an intuitive graphical user interface (GUI) that provides powerful and robust system management.

control file

A file that records the physical structure of a database and contains the database name, the names and locations of associated databases and online redo log files, the timestamp of the database creation, the current log sequence number, checkpoint information and various other records about the database's structure and health.

CR blocks received per transaction

The number of CR blocks shipped from the instance that has a block in exclusive access mode to the instance requesting a CR version of this block.

cr request retry

A statistic that quantifies a wait that is incurred whenever Oracle re-submits a consistent read request when Oracle detects that the holding instance is no longer available.

db block changes

A statistic that shows the number of current buffers obtained in exclusive mode for DML.

db block gets

A statistic that shows the number of current buffers obtained for a read.

DBWR cross-instance writes

Also known as forced writes, a statistic showing the number of writes that an instance has to perform to disk to make a previously exclusively held block available for another instance to read into its buffer cache. DBWR cross-instance writes are practically eliminated with Cache Fusion, unless you specify a value greater than 0 (zero) for the GC_FILES_TO_LOCKS parameter.

decision support system (DSS)

Database and application environments that help with decision support or data warehouse systems.

dedicated server

A server that requires a dedicated server process for each user process. There is one server process for each client. Oracle Net sends the address of an existing server process back to the client. The client then resends its connect request to the server address provided. Contrast this with the shared server.

degree of parallelism (DOP)

Specifies the number of processes, or threads, used in parallel execution. Each parallel process or thread can use one or two parallel execution processes depending on the SQL statement's complexity.

DFS Lock Handles

Pointers to global resources. To perform operations on global enqueue service resources, the process first needs to acquire a DFS handle.

dispatcher

A process that enables many clients to connect to the same server without the need for a dedicated server process for each client. A dispatcher handles and directs multiple incoming network session requests to shared server processes. See also shared server.

flow control messages sent

The number of flow-control (nullreq and nullack) messages that are sent by the LMS process.

flow control messages received

The number of flow-control (nullreq and nullack) messages received by the LMD process.

forced disk writes

The forced writing of a data block to disk by one instance when the data block is requested by another instance for a DML operation. Forced Writes are practically eliminated in Oracle9i with Cache Fusion, but they remain relevant if you specify 1:1 or 1:n releasable or fixed resources with the GC_FILES_TO_LOCKS parameter. In this case, Cache Fusion is disabled for that tablespace.

global cache bg acks

A wait event that only can occur during startup or shutdown of an instance when the LMS process finalizes its operations.

global cache busy

A wait event that occurs whenever a session has to wait for an ongoing operation on the resource to complete.

global cache cr cancel wait

A wait event that occurs whenever a session waits for the AST to complete for a canceled block access request. Cancelling the request is part of the Cache Fusion Write Protocol.

global cache converts

A statistic showing resource converts of buffer cache blocks. This statistic is incremented whenever GCS resources are converted from Null to Exclusive, Shared to Exclusive, or Null to Shared.

global cache convert time

The accumulated time that all sessions require to perform global conversions on GCS resources.

global cache convert timeouts

A statistic that is incremented whenever a resource operation times out.

global cache cr block flush time

The time waited for a log flush when a CR request is served. Once LGWR has completed flushing the changes to a buffer that is on the log flush queue, LMS can send it. It is part of the serve time.

global cache cr blocks received

When a process requests a consistent read for a data block that is not in its local cache, it sends a request to another instance. Once the request is complete, in other words, the buffer has been received, Oracle increments the statistic.

global cache cr block receive time

A statistic that records the total time required for consistent read requests to complete. In other words, it records the accumulated round-trip time for all requests for consistent read blocks.

global cache cr blocks served

A statistic showing the number of requests for a consistent read block served by LMS. Oracle increments this statistic when the block is sent.

global cache cr block build time

A statistic showing the time that the LMS process requires to create a consistent read block on the holding instance

global cache cr block send time

A statistic showing the time required by LMS to initiate a send of a consistent read block. For each request, timing begins when the block is sent and stops when the send has completed. This statistic only measures the time it takes to initiate the send; it does not measure the time elapsed before the block arrives at the requesting instance.

global cache cr cancel wait

Await event that occurs when a session waits for the acquisition interrupt to complete for a canceled CR request. Cancelling the CR request is part of the Cache Fusion write protocol.

global cache cr request

A wait event that occurs whenever a process has to wait for a pending CR request to complete. The process waited for either shared access to a block to be granted before reading the block from disk into the cache, or it waited for the LMS of the holding instance to send the block.

global cache current block flush time

A statistic showing the time it takes to flush the changes to a block to disk, otherwise known as a forced log flush, before the block is shipped to the requesting instance

global cache current block pin time

A statistic showing the time it takes to the pin the current block before shipping it to the requesting instance. Pinning a block is necessary to disallow further changes to the block while it is prepared to be shipped to another instance.

global cache current blocks received

A statistic showing the number of current blocks received from the holding instance over the interconnect.

global cache current block receive time

A statistic showing the accumulated round-trip time for all requests for current blocks

global cache current block send time

A statistic showing the time it takes to send the current block to the requesting instance over the interconnect.

global cache current blocks served

A statistic showing the number of current blocks shipped to the requesting instance over the interconnect

global cache freelist wait

A statistic showing when a wait event that occurs if Oracle must wait after it detects that the local element free list is empty.

global cache freelist waits

A statistic showing the number of times Oracle found the resource element free list empty.

global cache gets

A statistic showing the number of buffer gets that result in opening a new resource with the GCS.

global cache get time

A statistic showing the accumulated time of all sessions needed to open a GCS resource for a local buffer.

global cache initialization parameters

Initialization parameters that determine the size of the collection of global that protect the database buffers on all instances.

global cache null to S

A wait event that occurs whenever a session has to wait for a resource conversion to complete.

global cache null to X

A wait event that occurs whenever a session has to wait for this resource conversion to complete.

global cache open S

A wait event that occurs when a session has to wait for receiving permission for shared access to the requested resource.

global cache open X

A wait event that occurs when a session has to wait for receiving a exclusive access to the requested resource.

global cache S to X

A wait event that occurs whenever a session has to wait for this resource conversion to complete.

global cache pending ast

A wait event that can occur when a process waits for an acquisition interrupt before Oracle closes a resource element.

global cache pred cancel wait

A wait event that occurs when a session must wait for the acquisition interrupt to complete for a canceled predecessor read request. Cancelling a predecessor read request is part of the Cache Fusion write protocol.

global cache retry prepare

A wait event that occurs whenever Oracle fails to prepare a buffer for a consistent read or Cache Fusion request, and when Oracle cannot ignore or skip this failure.

Global Cache Service (GCS)

The process that implements Cache Fusion. It maintains block modes for blocks in the global role and is responsible for block transfers among instances. The Global Cache Service accomplishes these tasks using background processes such as the Global Cache Service process (LMS) and the Global Enqueue Service process (GES).

Global Cache Service Processes (LMSn)

The processes that handle remote Global Cache Service (GCS) messages. Real Application Clusters provides for up to 10 Global Cache Service Processes. The number of LMSn varies depending on the amount of messaging traffic among nodes in the cluster. The LMSn handle the acquisition interrupt and blocking interrupt requests from a remote instance for Global Cache Service resources. For cross-instance consistent read requests, LMSn creates a consistent read version of the block and sends it to the requesting instance. LMSn also controls the flow of messages to and from remote instances.

global database name

The full name of the database that uniquely identifies it from another database. The global database name is of the form database_name.database_domain, for example, sales.us.acme.com.

Global Enqueue Service (GES)

This service coordinates enqueues that are shared globally.

Global Enqueue Service Daemon (LMD)

The resource agent process that manages Global Enqueue Service resource requests. The LMD process also handles deadlock detection Global Enqueue Service requests. Remote resource requests are requests originating from another instance.

Global Enqueue Service Monitor (LMON)

The background process that monitors the entire cluster to manage global resources. LMON manages instance and process expirations and the associated recovery for the Global Cache and Global Enqueue Services. In particular, LMON handles the part of recovery associated with global resources. LMON-provided services are also known as cluster group services (CGS).

global lock async converts

A statistic showing the number of resources that Oracle converted from an incompatible mode.

global lock sync gets

A statistic showing the number of GCS resources that Oracle must open synchronously. Sync gets are mostly for GES resources (for example, library cache resources).

global lock async gets

A statistic showing the number of GES resources that Oracle must open asynchronously. Async gets are only used for GES resources and include the number of global cache gets.

global lock get time

A statistic showing the accumulated time for all GES resources that Oracle needed to open.

global lock sync converts

The number of GES resources that Oracle converted from an incompatible mode. Sync converts occur mostly for GES resources.

global lock convert time

A statistic showing the accumulated time for all global lock sync converts and global lock async converts.

hybrid database

A database that has both OLTP and Data Warehouse processing characteristics.

initialization parameter file

A file with parameter settings that initialize the database (initdb_name.ora). In the case of Real Application Clusters, it initializes the instances within a cluster (initsid.ora). The default single initialization parameter file is known as SPFILE.ORA.

instance

The combination of the System Global Area (SGA) and each process for the Oracle database. The memory and processes of an instance manage the associated database's data and serve the database users. Each instance has unique Oracle System Identifier (SID), instance name, instance number, rollback segments, and thread ID.

instance groups

Instance groups limit the number of instances that participate in a parallel operations. You can create any number of instance groups, each consisting of one or more instances. You can then specify which instance group is to be used for any or all parallel operations. Parallel execution servers will only be used on instances that are members of the specified instance group.

instance name

Represents the name of the instance and is used to uniquely identify a specific instance when several instances share common service names. The instance name is identified by the INSTANCE_NAME parameter in the initialization parameter file. The instance name is identical to Oracle System Identifier (SID).

instance number

A number that associates extents of data blocks with particular instances. The instance number enables you to start up an instance and ensure that it uses the extents allocated to it for inserts and updates. This ensures that it does not use space allocated for other instances. The instance cannot use data blocks in another free list unless the instance is restarted with that instance number.

You can use various SQL options with the INSTANCE_NUMBER initialization parameter to associate extents of data blocks with instances.

The instance number is depicted by the INSTANCE_NUMBER parameter in the instance initialization file, initsid.ora.

interconnect

The communication link between the nodes.

Inter-Process Communication (IPC)

A high-speed operating system-dependent transport component. The IPC transfers messages between instances on different nodes. Also referred to as the interconnect.

listener

A listener configuration file that identifies the protocol addresses on which the listener is accepting connection requests and the services the listener listens for.

load balancing

Load balancing is the even distribution of active database connections among instances. In the context of parallel execution, load balancing refers to the distribution of parallel execution server processes to spread work among the CPUs and memory resources.

lock buffers for read

A statistic showing the number of up-converts from Null to Shared.

lock gets per transaction

A statistic showing the number of global lock sync gets and global lock async gets per transaction.

lock converts per transaction

A statistic showing the number of global local sync converts and global lock async converts per transaction.

messages flow controlled

The number of messages intended to be sent directly but that are instead queued and delivered later by LMD/LMS.

messages received

The number of messages received by the LMD process.

messages sent directly

The number of messages sent directly by Oracle processes.

messages sent indirectly

The number of messages explicitly queued by Oracle processes.

node

A node is machine on which one or more instances reside.

operating system context switches

Operating system context switches occur when a thread's time allotment has elapsed, when a thread with a higher priority has become ready to run, or when a running thread needs to wait, for example, for I/O to complete.

operating system-dependent (OSD) clusterware

Software that consists of several software components developed by Oracle or other vendors. The OSD layer maps the key operating system/cluster-ware services required for proper operation of Real Application Clusters.

Oracle Data Gatherer

The Oracle Data Gatherer collects performance statistics for the Oracle Performance Manager. You must install the Oracle Data Gatherer on a node on your network.

Oracle Enterprise Manager

A system management tool that provides an integrated solution for centrally managing your heterogeneous environment. Oracle Enterprise Manager combines a graphical console, management server, Oracle Intelligent Agent, repository database, and tools to provide an integrated, comprehensive systems management platform for managing Oracle products.

Oracle Enterprise Manager Console

A suite of GUI tools that make up the Oracle Enterprise Manager product.

Oracle Intelligent Agent

A process that runs on each of the node that functions as the executor of jobs and events sent by the console by way of the Management Server. The Oracle Intelligent Agent ensures high availability since the agent can function regardless of the status of the Console or network connections.

Oracle Net

A software component that enables connectivity. It includes a core communication layer called the Oracle Net foundation layer and network protocol support. Oracle Net enables services and their applications to reside on different computers and communicate as peer applications. The main function of Oracle Net is to establish network sessions and transfer data between a client machine and a server or between two servers. Once a network session is established, Oracle Net acts as a data courier for the client and the server.

Oracle Performance Manager

An add-on application for Oracle Enterprise Manager that offers a variety of tabular and graphic performance statistics for Real Application Clusters. The statistics represent the aggregate performance for all instances.

Oracle Real Application Clusters

A breakthrough architecture that enables clusters to access a shared database. Real Application Clusters includes the software component that provides the necessary Real Application Clusters scripts, initialization files, and datafiles to make the Oracle9i Enterprise Edition an Oracle9i Real Application Clusters database.

Oracle System Identifier (SID)

A name that identifies a specific instance of a running pre-release 8.1 Oracle database. For a Real Application Clusters database, each node within the cluster has an instance referencing the database. The database name, specified by the DB_NAME parameter in the initdb_name.ora file, and unique thread ID make up each node's SID. The thread ID starts at 1 for the first instance in the cluster, and is incremented by 1 for the next instance, and so on.

Oracle9i Enterprise Edition

Oracle9i Enterprise Edition is an object-relational database management system (ORDBMS). It provides the applications and files to manage a database. All other Real Application Clusters components are layered on top of the Oracle9i Enterprise Edition.

parallel automatic tuning

A feature that automatically controls values for all parameters related to parallel execution. These parameters affect several aspects of server processing, namely, the degree of parallelism (DOP), the adaptive multiuser feature, and memory sizing. Initialize and automatically tune parallel execution by setting the initialization parameter PARALLEL_AUTOMATIC_TUNING to true.

parallel execution

Multiple processes operating together to complete a single database transaction. Parallel execution works on both single instance and cluster database Oracle installations. Parallel execution is also referred to parallel query.

physical reads

A statistic showing the number of disk reads that had to be performed when a request for a data block could not be satisfied from a local cache.

physical writes

The number of write I/Os performed by the DBWNn processes. This number includes the number of DBWR cross instance writes (forced writes) in Oracle9i when GC_FILES_TO_LOCKS is set. Setting GC_FILES_TO_LOCKS for a particular datafile will enable the use of the old ping protocol, and will not leverage the Cache Fusion architecture.

raw devices

Disks or partitions on disk drives that do not have a file system set up on them. Raw devices are used for Real Application Clusters since they enable the sharing of disks.

raw volumes

See raw devices.

Real Application Clusters

See Oracle Real Application Clusters.

Recovery Manager (RMAN)

An Oracle tool that enables you to back up, copy, restore, and recover datafiles, control files, and archived redo logs. It is included with the Oracle server and does not require separate installation. You can invoke RMAN as a command line utility from the operating system (O/S) prompt or use the GUI-based Enterprise Manager Backup Manager.

remote instance undo block writes

A statistic showing the number of undo blocks written to disk by DBWn as part of a forced write.

remote instance undo header writes

A statistic showing the number of rollback segment header blocks written to disk by DBWn as part of a forced write.

repository database

A database, such as that used by Oracle Enterprise Manager, that is a set of tables in an Oracle database, to store data to manage Real Application Clusters environments. This database is separate from any shared Real Application Clusters database on the nodes.

seed database

A preconfigured, ready-to-use database that requires minimal user input to create.

server clustering

See Oracle Real Application Clusters.

Server Management

A comprehensive, integrated system management solution for managing Real Application Clusters environments. Server Management enables you to manage cluster databases in heterogeneous environments. Server Management is part of the open client/server architecture of Oracle Enterprise Manager. In addition to managing cluster databases, Server Management enables you to schedule jobs, perform event management, monitor performance, and obtain statistics to monitor Real Application Clusters performance.

service name

A logical representation of a database, which is the way a database is presented to clients. A database can be presented as multiple services and a service can be implemented as multiple database instances. The service name is a string that is the global database name, a name comprised of the database name (DB_NAME) and domain name (DB_DOMAIN), entered during installation or database creation.

service registration

A feature by which the PMON process (or shared server Dispatcher processes when using shared server) automatically registers information with a listener. Because this information is registered with the listener, you do not need to configure the listener.ora file with this static information.

shared server

A server configured to enable many user processes to share very few server processes. This means increases the number of users that can be supported. With shared server, many user processes connect to a dispatcher. Contrast this with dedicated server.

star schemas

Query-centric schemas that when represented in a diagram have a fact table at the center. The fact table usually contains the data element that is central to queries operating against the schema. A fact table is often quite large and is surrounded by several dimension tables that contain data that are attributes of the data in the fact table. Star schemas simplify query development because it is intuitive as to how to join attributes in the dimension tables with the fact table data. Star schemas are best suited for data warehouse environments and are thus less useful for OTLP environments.

striping

Refers to the interleaving of a related block of data across disks. If you properly implement striping, then it reduces I/O and improves performance. Because striping software is operating system-dependent, rely on your vendor documentation to ensure proper installation and configuration.

Transmission Control Protocol/Interconnect Protocol (TCP/IP)

A set of protocols that enable cooperating computers to share resources across a network.

thread ID

The number of a redo thread for an instance. Any available redo thread number can be used, but an instance cannot use the same thread number as another instance.

transaction monitor

A class of software products that provide a transaction execution layer on top of the operating system. Transaction monitors combine database updates and submit them to a database. In doing this, the transaction monitor manages some of the consistency and correctness of the database. The monitor ensures that the rules of transaction atomicity are adhered to; updates take place completely or not at all. The advantages of using transaction monitors include increased throughput.

transparent application failover (TAF)

A runtime failover mechanism for high-availability environments, such as Real Application Clusters and Oracle Real Application Clusters Guard, that refers to the failover and re-establishment of application-to-service connections. It enables client applications to automatically reconnect to the database if the connection fails, and optionally resume a SELECT statement that was in progress. This reconnect happens automatically from within the Oracle Call Interface (OCI) library.

User Datagram Protocol (UDP)

A protocol similar to TCP/IP. However, it is simpler to administer. It is considered less reliable than TCP/IP because, for example, it does not guarantee message ordering.

User-mode IPC

An IPC-based (Inter-process Communication) protocol that directly accesses network hardware. As opposed to kernel-mode IPC, with user-mode IPC the protocol avoids the overhead of copying data into kernel space, making system calls, and incurring context switches.

Virtual Interface Architecture (VIA)

An implementation of user mode IPC.


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