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Oracle RAC concepts
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Oracle RAC Interview Question & Answer. 1. Where are the Clusterware files stored on a RAC environment? The Clusterware is installed on each node (on an Oracle Home) and on the shared disks (the voting disks and the CSR file) 2. Where are the database software files stored on a RAC environment? The base software is installed on each node of the cluster and the database storage on the shared disks. 3. What kind of storage we can use for the shared Clusterware files? - OCFS (Release 1 or 2) - raw devices - third party cluster file system such as GPFS or Veritas 4. What kind of storage we can use for the RAC database storage? - OCFS (Release 1 or 2) - ASM - raw devices - third party cluster file system such as GPFS or Veritas 5. What is a CFS? A cluster File System (CFS) is a file system that may be accessed (read and writ e) by all members in a cluster at the same time. This implies that all members o f a cluster have the same view. 6. What is an OCFS2? The OCFS2 is the Oracle (version 2) Cluster File System which can be used for th e Oracle Real Application Cluster. 7. Which files can be placed on an Oracle Cluster File System? - Oracle Software installation (Windows only) - Oracle files (controlfiles, datafiles, redologs, files described by the bfile datatype) - Shared configuration files (spfile) - OCR and voting disk - Files created by Oracle during runtime Note: There are some platform specific limitations. 8. Do you know another Cluster Vendor? HP Tru64 Unix, Veritas, Microsoft 9. How is possible to install a RAC if we don t have a CFS? This is possible by using a raw device. 10. What is a raw device? A raw device is a disk drive that does not yet have a file system set up. Raw de vices are used for Real Application Clusters since they enable the sharing of di sks. 11. What is a raw partition? A raw partition is a portion of a physical disk that is accessed at the lowest p ossible level. A raw partition is created when an extended partition is created and logical partitions are assigned to it without any formatting. Once formattin g is complete, it is called cooked partition. 12. When to use CFS over raw? A CFS offers:
- Simpler management - Use of Oracle Managed Files with RAC - Single Oracle Software installation - Autoextend enabled on Oracle datafiles - Uniform accessibility to archive logs in case of physical node failure - With Oracle_Home on CFS, when you apply Oracle patches CFS guarantees that the updated Oracle_Home is visible to all nodes in the cluster. Note: This option is very dependent on the availability of a CFS on your platfor m. 13. When to use raw over CFS? - Always when CFS is not available or not supported by Oracle. - The performance is very, very important: Raw devices offer best performance wi thout any intermediate layer between Oracle and the disk. Note: Autoextend fails on raw devices if the space is exhausted. However the spa ce could be added online if needed. 14. What CRS is? Oracle RAC 10g Release 1 introduced Oracle Cluster Ready Services (CRS), a platf orm-independent set of system services for cluster environments. In Release 2, O racle has renamed this product to Oracle Clusterware. 15. What is VIP IP used for? It returns a dead connection IMMIDIATELY, when its primary node fails. Without u sing VIP IP, the clients have to wait around 10 minutes to receive ORA-3113: end of file on communications channel . However, using Transparent Application Failove r (TAF) could avoid ORA-3113. 16. Why we need to have configured SSH or RSH on the RAC nodes? SSH (Secure Shell,10g+) or RSH (Remote Shell, 9i+) allows oracle UNIX account conn ecting to another RAC node and copy/ run commands as the local oracle UNIX account . 17. Is the SSH, RSH needed for normal RAC operations? No. SSH or RSH are needed only for RAC, patch set installation and clustered dat abase creation. 18. Do we have to have Oracle RDBMS on all nodes? Each node of a cluster that is being used for a clustered database will typicall y have the RDBMS and RAC software loaded on it, but not actual data files (these need to be available via shared disk). 19. What are the restrictions on the SID with a RAC database? Is it limited to 5 characters? The SID prefix in 10g Release 1 and prior versions was restricted to five charac ters by install/ config tools so that an ORACLE_SID of up to max of 5+3=8 charac ters can be supported in a RAC environment. The SID prefix is relaxed up to 8 ch aracters in 10g Release 2, see bug 4024251 for more information. 20. Does Real Application Clusters support heterogeneous platforms? The Real Application Clusters do not support heterogeneous platforms in the same cluster. 21. Are there any issues for the interconnect when sharing the same switch as th e public network by using VLAN to separate the network? RAC and Clusterware deployment best practices suggests that the interconnect (pr ivate connection) be deployed on a stand-alone, physically separate, dedicated s witch. On big network the connections could be instable.
22. What is the Load Balancing Advisory? To assist in the balancing of application workload across designated resources, Oracle Database 10g Release 2 provides the Load Balancing Advisory. This Advisor y monitors the current workload activity across the cluster and for each instanc e where a service is active; it provides a percentage value of how much of the t otal workload should be sent to this instance as well as service quality flag. 23. How many nodes are supported in a RAC Database? With 10g Release 2, we support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database. Currently DBCA has a bug where it will not go beyond 63 instances. There is also a documentation bug for the max-instances parameter. With 10g Release 1 the Maximum is 63.
24. What is the Cluster Verification Utiltiy (cluvfy)? The Cluster Verification Utility (CVU) is a validation tool that you can use to check all the important components that need to be verified at different stages of deployment in a RAC environment. 25. What versions of the database can I use the cluster verification utility (cl uvfy) with? The cluster verification utility is release with Oracle Database 10g Release 2 b ut can also be used with Oracle Database 10g Release 1. 26. If I am using Vendor Clusterware such as Veritas, IBM, Sun or HP, do I still need Oracle Clusterware to run Oracle RAC 10g? Yes. When certified, you can use Vendor Clusterware however you must still insta ll and use Oracle Clusterware for RAC. Best Practice is to leave Oracle Clusterw are to manage RAC. For details see Metalink Note 332257.1 and for Veritas SFRAC see 397460.1. 27. Is RAC on VMWare supported? Yes. 28. What is hangcheck timer used for ? The hangcheck timer checks regularly the health of the system. If the system han gs or stop the node will be restarted automatically. There are 2 key parameters for this module: -> hangcheck-tick: this parameter defines the period of time between checks of s ystem health. The default value is 60 seconds; Oracle recommends setting it to 3 0seconds. -> hangcheck-margin: this defines the maximum hang delay that should be tolerate d before hangcheck-timer resets the RAC node. 29. Is the hangcheck timer still needed with Oracle RAC 10g? Yes. 30. What files can I put on Linux OCFS2? For optimal performance, you should only put the following files on Linux OCFS2: - Datafiles - Control Files - Redo Logs - Archive Logs - Shared Configuration File (OCR) - Voting File - SPFILE 31. Is it possible to use ASM for the OCR and voting disk?
No, the OCR and voting disk must be on raw or CFS (cluster file system). 32. Can I change the name of my cluster after I have created it when I am using Oracle Clusterware? No, you must properly uninstall Oracle Clusterware and then re-install. 33. What the O2CB is? The O2CB is the OCFS2 cluster stack. OCFS2 includes some services. These service s must be started before using OCFS2 (mount/ format the file systems). 34. What the OCR file is used for? OCR is a file that manages the cluster and RAC configuration. 35. What the Voting Disk file is used for? The voting disk is nothing but a file that contains and manages information of a ll the node memberships. 36. What is the recommended method to make backups of a RAC environment? RMAN to make backups of the database, dd to backup your voting disk and hard copies of the OCR file. 37. What command would you use to check the availability of the RAC system? crs_stat -t -v (-t -v are optional) 38. What is the minimum number of instances you need to have in order to create a RAC? You can create a RAC with just one server. 39. Name two specific RAC background processes RAC processes are: LMON, LMDx, LMSn, LKCx and DIAG. 40. Can you have many database versions in the same RAC? Yes, but Clusterware version must be greater than the greater database version. 41. What was RAC previous name before it was called RAC? OPS: Oracle Parallel Server 42. What RAC component is used for communication between instances? Private Interconnect. 43. What is the difference between normal views and RAC views? A RAC view has the prefix G. For example, GV$SESSION instead of V$SESSION 44. Which command will we use to manage (stop, start) RAC services in command-l ine mode? srvctl 45. How many alert logs exist in a RAC environment? A- One for each instance. 46. What are Oracle Clusterware Components Voting Disk Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case o f network failures. The voting disk must reside on shared disk. Oracle Cluster Registry (OCR) Maintains cluster configuration information as wel l as configuration information about any cluster database within the cluster. Th e OCR must reside on shared disk that is accessible by all of the nodes in your cluster 47. How do you backup voting disk
#dd if=voting_disk_name of=backup_file_name 48. How do I identify the voting disk location #crsctl query css votedisk 49. How do I identify the OCR file location check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform) or #ocrcheck 50. What is SCAN? Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RA C) 11g Release 2 feature that provides a single name for clients to access an Or acle Database running in a cluster. The benefit is clients using SCAN do not nee d to change if you add or remove nodes in the cluster. Topic #2
Re: RAC issues and mostly asked Interview questions Posted: Apr 11, 2012 1:41 AM in response to: fjfranken in response to: fjfrank en Click to report abuse... Click to reply to this thread Reply Please find below RAC Interview question and answer. What is RAC? RAC stands for Real Application cluster. It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance f ailover, media failover features. What is RAC and how is it different from non RAC databases? RAC stands for Real Application Cluster, you have n number of instances running in their own separate nodes and based on the shared storage. Cluster is the key component and is a collection of servers operations as one unit. RAC is the best solution for high performance and high availably. Non RAC databases has single point of failure in case of hardware failure or server crash. Give the usage of srvctl : srvctl start instance -d db_name -i "inst_name_list" [-o start_options] srvctl stop instance -d name -i "inst_name_list" [-o stop_options] srvctl stop instance -d orcl -i "orcl3,orcl4" -o immediate srvctl start database -d name [-o start_options] srvctl stop database -d name [-o stop_options] srvctl start database -d orcl -o mount Mention the Oracle RAC software components : Oracle RAC is composed of two or more database instances. They are composed of M emory structures and background processes same as the single instance database.O racle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Ca che Service) that enable cache fusion.Oracle RAC instances are composed of follo wing background processes: ACMSAtomic Controlfile to Memory Service (ACMS) GTX0-jGlobal Transaction Process LMONGlobal Enqueue Service Monitor LMDGlobal Enqueue Service Daemon LMSGlobal Cache Service Process LCK0Instance Enqueue Process
RMSnOracle RAC Management Processes (RMSn) RSMNRemote Slave Monitor What is GRD? GRD stands for Global Resource Directory. The GES and GCS maintains records of t he statuses of each datafile and each cahed block using global resource director y.This process is referred to as cache fusion and helps in data integrity. What are the different network components are in 10g RAC? public, private, and vip components Private interfaces is for intra node communication. VIP is all about availabilit y of application. When a node fails then the VIP component fail over to some oth er node, this is the reason that all applications should based on vip components means tns entries should have vip entry in the host list Give Details on ACMS: ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment A CMS is an agent that ensures a distributed SGA memory update(ie)SGA updates are globally committed on success or globally aborted in event of a failure. What is Cache Fusion? Cache fusion is the mechanism to transfer the data block from memory to memory o f one node to the other.If two nodes require the same block for query or update, the block must be transfered from the cache of one node to the other. RAC syste m must equipped with low-latency and high speed inter-connect to make it happen. Give Details on Cache Fusion: Oracle RAC is composed of two or more instances. When a block of data is read fr om datafile by an instance within the cluster and another instance is in need of the same block,it is easy to get the block image from the insatnce which has th e block in its SGA rather than reading from the disk. To enable inter instance c ommunication Oracle RAC makes use of interconnects. The Global Enqueue Service(G ES) monitors and Instance enqueue process manages the cahce fusion. Cache Fusion is essentially a memory-to-memory transfer of data between the node s in the RAC environment. Before Cache Fusion, a node was required to write some of the data to disk before it could be transferred to the next node in the clus ter. Cache Fusion does a straight memory-to-memory transfer. In addition, each n ode's SGA has a map of what data is contained in the other node's data caches. The performance improvement is phenomenal. Oracle leverages the vendor's high sp eed interconnects between the nodes to achieve the cache-to-cache data transfers . Before Cache Fusion, when you added a node to the cluster to increase performa nce of the application, it didn't always provide you with the performance improv ement that you hoped for. With Cache Fusion, you can easily cost justify the add ition of another node into a RAC cluster to increase the performance of the appl ication running on it. Oracle sales pitches describe it as 'near linear horizont al scalability'. What are the major RAC wait events? In a RAC environment the buffer cache is global across all instances in the clus ter and hence the processing differs.The most common wait events related to this are gc cr request and gc buffer busy GC CR request :the time it takes to retrieve the data from the remote cache Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned q ueries will increase the amount of data blocks requested by an Oracle session. T he more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.) GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block. Give details on GTX0-j : The process provides transparent support for XA global transactions in a RAC env
ironment.The database autotunes the number of these processes based on the workl oad of XA global transactions. Give details on LMON: This process monitors global enques and resources across the cluster and perform s global enqueue recovery operations.This is called as Global Enqueue Service Mo nitor. Give details on LMD: This process is called as global enqueue service daemon. This process manages in coming remote resource requests within each instance. Give details on LMS: This process is called as Global Cache service process.This process maintains st atuses of datafiles and each cahed block by recording information in a Global Re source Dectory(GRD).This process also controls the flow of messages to remote in stances and manages global data block access and transmits block images between the buffer caches of different instances.This processing is a part of cache fusi on feature. Give details on LCK0: This process is called as Instance enqueue process.This process manages non-cach e fusion resource requests such as libry and row cache requests. Give details on RMSn: This process is called as Oracle RAC management process.These pocesses perform m anagability tasks for Oracle RAC.Tasks include creation of resources related Ora cle RAC when new instances are added to the cluster. Give details on RSMN: This process is called as Remote Slave Monitor.This process manages background s lave process creation andd communication on remote instances. This is a backgrou nd slave process.This process performs tasks on behalf of a co-ordinating proces s running in another instance. What components in RAC must reside in shared storage? All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-awar e shred storage. What is the significance of using cluster-aware shared storage in an Oracle RAC environment? All instances of an Oracle RAC can access all the datafiles,control files, SPFIL E's, redolog files when these files are hosted out of cluster-aware shared stora ge which are group of shared disks. Give few examples for solutions that support cluster storage: ASM(automatic storage management),raw disk devices,network file system(NFS), OCF S2 and OCFS(Oracle Cluster Fie systems). What is an interconnect network? An interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only t he nodes in the cluster can access. How can we configure the cluster interconnect? Configure User Datagram Protocol(UDP) on Gigabit ethernet for cluster interconne ct.On unix and linux systems we use UDP and RDS(Reliable data socket) protocols to be used by Oracle Clusterware.Windows clusters use the TCP protocol. Can we use crossover cables with Oracle Clusterware interconnects?
No, crossover cables are not supported with Oracle Clusterware intercnects. What is the use of cluster interconnect? Cluster interconnect is used by the Cache fusion for inter instance communicatio n. How do users connect to database in an Oracle RAC environment? Users can access a RAC database using a client/server configuration or through o ne or more middle tiers ,with or without connection pooling.Users can use oracle services feature to connect to database. What is the use of a service in Oracle RAC environment? Applications should use the services feature to connect to the Oracle database.S ervices enable us to define rules and characteristics to control how users and a pplications connect to database instances. What are the characteristics controlled by Oracle services feature? The charateristics include a unique name, workload balancing and failover option s,and high availability characteristics. What enables the load balancing of applications in RAC? Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database. What is a virtual IP address or VIP? A virtl IP address or VIP is an alternate IP address that the client connectins use instead of the standard public IP address. To configureVIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the s ame subnet as the public network. What is the use of VIP? If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connecti ons. Give situations under which VIP address failover happens: VIP addresses failover happens when the node on which the VIP address runs fails , all interfaces for the VIP address fails,all interfaces for the VIP address ar e disconnected from the network. What is the significance of VIP address failover? When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to wait for TC P connection timeout messages. What are the administrative tools used for Oracle RAC environments? Oracle RAC cluster can be administered as a single image using OEM(Enterprise Ma nager),SQL*PLUS,Servercontrol(SRVCTL),clusterverificationutility(cvu),DBCA,NETCA How do we verify that RAC instances are running? Issue the following query from any one node connecting through SQL*PLUS. $connect sys/sys as sysdba SQL>select * from V$ACTIVE_INSTANCES; The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column. What is FAN? Fast application Notification as it abbreviates to FAN relates to the events rel ated to instances,services and nodes.This is a notification mechanism that Oracl e RAc uses to notify other processes about the configuration and service level i nformation that includes service status changes such as,UP or DOWN events.Applic
ations can respond to FAN events and take immediate action. Where can we apply FAN UP and DOWN events? FAN UP and FAN DOWN events can be applied to instances,services and nodes. State the use of FAN events in case of a cluster configuration change? During times of cluster configuration changes,Oracle RAC high availability frame work publishes a FAN event immediately when a state change occurs in the cluster .So applications can receive FAN events and react immediately.This prevents appl ications from polling database and detecting a problem after such a state change . Why should we have seperate homes for ASm instance? It is a good practice to have ASM home seperate from the database hom(ORACLE_HOM E).This helps in upgrading and patching ASM and the Oracle database software ind ependent of each other.Also,we can deinstall the Oracle database software indepe ndent of the ASM instance. What is the advantage of using ASM? Having ASM is the Oracle recommended storage option for RAC databases as the ASM maximizes performance by managing the storage configuration across the disks.AS M does this by distributing the database file across all of the available storag e within our cluster database environment. What is rolling upgrade? It is a new ASM feature from Database 11g.ASM instances in Oracle database 11g r elease(from 11.1) can be upgraded or patched using rolling upgrade feature. This enables us to patch or upgrade ASM nodes in a clustered environment without aff ecting database availability.During a rolling upgrade we can maintain a function al cluster while one or more of the nodes in the cluster are running in differen t software versions. Can rolling upgrade be used to upgrade from 10g to 11g database? No,it can be used only for Oracle database 11g releases(from 11.1). State the initialization parameters that must have same value for every instance in an Oracle RAC database: Some initialization parameters are critical at the database creation time and mu st have same values.Their value must be specified in SPFILE or PFILE for every i nstance.The list of parameters that must be identical on every instance are give n below: ACTIVE_INSTANCE_COUNT ARCHIVE_LAG_TARGET COMPATIBLE CLUSTER_DATABASE CLUSTER_DATABASE_INSTANCE CONTROL_FILES DB_BLOCK_SIZE DB_DOMAIN DB_FILES DB_NAME DB_RECOVERY_FILE_DEST DB_RECOVERY_FILE_DEST_SIZE DB_UNIQUE_NAME INSTANCE_TYPE (RDBMS or ASM) PARALLEL_MAX_SERVERS REMOTE_LOGIN_PASSWORD_FILE UNDO_MANAGEMENT What is ORA-00603: ORACLE server session terminated by fatal error or ORA-29702: error occurred in Cluster Group Service operation? RAC node name was listed in the loopback address...
Can the DML_LOCKS and RESULT_CACHE_MAX_SIZE be identical on all instances? These parameters can be identical on all instances only if these parameter value s are set to zero. What two parameters must be set at the time of starting up an ASM instance in a RAC environment?The parameters CLUSTER_DATABASE and INSTANCE_TYPE must be set. Mention the components of Oracle clusterware: Oracle clusterware is made up of components like voting disk and Oracle Cluster Registry(OCR). What is a CRS resource? Oracle clusterware is used to manage high-availability operations in a cluster.A nything that Oracle Clusterware manages is known as a CRS resource.Some examples of CRS resources are database,an instance,a service,a listener,a VIP address,an application process etc. What is the use of OCR? Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry). How does a Oracle Clusterware manage CRS resources? Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry). Name some Oracle clusterware tools and their uses? OIFCFG - allocating and deallocating network interfaces OCRCONFIG - Command-line tool for managing Oracle Cluster Registry OCRDUMP - Identify the interconnect being used CVU - Cluster verification utility to get status of CRS resources What are the modes of deleting instances from ORacle Real Application cluster Da tabases? We can delete instances using silent mode or interactive mode using DBCA(Databas e Configuration Assistant). How do we remove ASM from a Oracle RAC environment? We need to stop and delete the instance in the node first in interactive or sile nt mode.After that asm can be removed using srvctl tool as follows: srvctl stop asm -n node_name srvctl remove asm -n node_name We can verify if ASM has been removed by issuing the following command: srvctl config asm -n node_name How do we verify that an instance has been removed from OCR after deleting an in stance? Issue the following srvctl command: srvctl config database -d database_name cd CRS_HOME/bin ./crs_stat How do we verify an existing current backup of OCR? We can verify the current backup of OCR using the following command : ocrconfig -showbackup What are the performance views in an Oracle RAC environment? We have v$ views that are instance specific. In addition we have GV$ views calle d as global views that has an INST_ID column of numeric data type.GV$ views obta in information from individual V$ views. What are the types of connection load-balancing? There are two types of connection load-balancing:server-side load balancing and client-side load balancing.
What is the difference between server-side and client-side connection load balan cing? Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing ad visory to redirect connections to the instance providing best service. What are the three greatest benefits that RAC provides?? The three main benefits are availability, scalability, and the ability to use lo w cost commodity hardware. RAC allows an application to scale vertically, by add ing CPU, disk and memory resources to an individual server. But RAC also provide s horizontal scalability, which is achieved by adding new nodes into the cluster . RAC also allows an organization to bring these resources online as they are ne eded. This can save a small or midsize organization a lot of money in the early stages of a project. In a RAC environment, if a node in the cluster fails, the application continues to run on the surviving nodes contained in the cluster. If your application is c onfigured correctly, most users won't even know that the node they were running on became unavailable. What are the major RAC wait events? In a RAC environment the buffer cache is global across all instances in the clus ter and hence the processing differs.The most common wait events related to this are gc cr request and gc buf fer busy GC CR request: the time it takes to retrieve the data from the remote cache Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned q ueries will increase the amount of data blocks requested by an Oracle session. The more blocks requested typically means the mo re often a block will need to be read from a remote instance via the interconnec t.) GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block. What are the different network components in Oracle 10g RAC? We have public, private, and VIP components. Private interfaces is for intra nod e communication. VIP is all about availability of application. When a node fails then the VIP component will fail over to some other node, this is the reason th at all applications should be based on VIP components. This means that tns entr ies should have VIP entry in the host list.