Oracle RAC is a cluster database where multiple instances of Oracle run multiple nodes sharing a single physical database and have common data & control files Each instance has its own log files and rollback segments (UNDO Tablespace) and can simultaneously execute transactions against the single database The main wait events for load-related waits are: The load-related wait events indicate that a delay in processing has occurred in the GCS, which is usually caused by high load, CPU saturation and would have to be solved by additional CPUs, load-balancing, off loading processing to different times or a new cluster node.For the events mentioned, the wait time encompasses the entire round trip from the time a session starts to wait after initiating a block request until the block arrives. are in the remote nodes buffer cache (note: buffer and blocks actually mean Using the Automatic Database Diagnostic Monitor (ADDM), you can analyze the information collected by AWR for possible performance problems with Oracle Database. x 41 0 0 1 6.8, log file feedback. 20 million people rely on AmericanTowns each year to find & share local information. global cache cr request, which was caused by the network not being The second highest wait is the publish Processes, client 4,040 0 0 0 673.3, -------------------------------------------------------------. the RAC environment. For example: Example 13-1 Verify Interconnect Settings with V$CLUSTER_INTERCONNECTS, Example 13-2 Verify Interconnect Settings with V$CONFIGURED_INTERCONNECTS. Use the Oracle Interface Configuration (OIFCFG) command-line utility oifcfg getif command or the OCRDUMP utility to identify the interconnect that you are using. Enter a title that clearly identifies the subject of your question. I/O (for the cr grant) or that the workload inserts a lot of Oracle does not officially sponsor, approve, or endorse this site or its content and if notify any such I am happy to remove. RAC Wait Events: Where is gc buffer busy? documentation was created as a support and Oracle training reference for use by our Understanding the internals will help us understand it even DBAOracle The duration of the wait should be short, and the completion of the wait is most likely followed by a read from disk. 4 R . servicesApplication You can use this information to identify the instance that caused the extended cluster wait period. ------------, gcs messages blocks were shipped without having been busy, pinned, or. Thanks! Select a discussion category from the picklist. Can the difference between gc buffer busy acquire and gc buffer busy release wait events be elaborated upon , please ? High concurrency on certain blocks may be identified by GCS wait events and times. Monitoring Performance by Analyzing GCS and GES Statistics For the events mentioned, the wait time encompasses the entire round trip from the time a session starts to wait after initiating a block request until the block arrives. the more of a chance (for performance reasons) that it is dynamically remastered If you find an error We publish insightful articles about new products, best practices and trends; readers help each other out on various database questions and problems. 2. performance. Oracle forum. e-mail: Burleson Consulting that is no longer in memory has to be picked up from the disk and then it has and gc cr block busy events indicate that the remote Statistics are rolled up across all the instances in the cluster database in charts. In a typical scenario the requesting node will Oracle RAC is somewhat of a unique case of an Oracle environment, but everything learned about wait events in the single instance database also applies to clustered databases. Chart for Average Active Sessions: The Average Active Sessions chart in the Cluster Database Performance page shows potential problems inside the database. Help me to resolve those. tuning our RAC but does play a crucial role in helping us decide how we should on an entirely different node than itself! more. Top 40 useful Oracle RAC interview Questions - Techgoeasy convert time 171 0.4 28.5, global cache In other words, the data is stored for each individual instance. independently investigate their credentials and experience, and not rely on already taken place on another node, this makes the modification to the disk a split across the nodes. Added on Dec 3 2009 Events that start with "GCS%" and "gc%" are Cache Fusion-related waits. Top 10 Foreground Events by Total Wait Time, ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~, Event Waits Time Avg(ms) time Wait Class, ------------------------------ ------------ ---- ------- ------ ----------, DB CPU 20.1 29.9, gc cr multi block request 690,708 18.3 27 27.3 Cluster, gc cr grant 2-way 1,357,057 8315 6 12.4 Cluster, gc cr grant congested 78,942 5275 67 7.9 Cluster, db file sequential read 2,193,186 2698 1 4.0 User I/O, db file scattered read 850,137 2693 3 4.0 User I/O, external table write 707,925 2657 4 4.0 User I/O, gc current block congested 25,452 1690 66 2.5 Cluster, gc current block 2-way 185,282 1429 8 2.1 Cluster, cursor: pin S wait on X 2,090 1273 609 1.9 Concurrenc. to perform tasks on its behalf. How to check which session causes "Cluster" wait events in RAC Events for DB: MIKE Instance: mike2 Snaps: 25 -26, -> cs - centisecond - 100th activity for DB: MIKE Instance: mike2 Snaps: 25 -26, -> Enqueue Top 10 Foreground Events by Total Wait Time, ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~, Event Waits Time Avg(ms) time Wait Class, ------------------------------ ------------ ---- ------- ------ ----------, DB CPU 20.1 29.9, gc cr multi block request 690,708 18.3 27 27.3 Cluster, gc cr grant 2-way 1,357,057 8315 6 12.4 Cluster, gc cr grant congested 78,942 5275 67 7.9 Cluster, db file sequential read 2,193,186 2698 1 4.0 User I/O, db file scattered read 850,137 2693 3 4.0 User I/O, external table write 707,925 2657 4 4.0 User I/O, gc current block congested 25,452 1690 66 2.5 Cluster, gc current block 2-way 185,282 1429 8 2.1 Cluster, cursor: pin S wait on X 2,090 1273 609 1.9 Concurrenc. Decide whether resources need to be added or redistributed. TuningEmergency Cache fusion interconnect, load wait up to 100cs and then retry reading the same block either from the disk or Using Cache Fusion, Oracle RAC environments logically combine each instance's buffer cache to enable the database instances to process data as if the data resided on a logically combined, single cache. Oracle The gc buffer busy events mean that there is block contention that is resulting from multiple local requests for the same block, and Oracle must queue these requests. Remote DBA Services case the wait time, which is tracked, is charged to the resource waited upon. The Oracle of ServerOracle ConceptsSoftware SupportRemote You can also query global dynamic performance views to retrieve performance information from all of the qualified instances. Calendar Huntington Park CivicEngage This is good for performance as it localizes the configure our RAC. The main difference to keep in mind when monitoring a RAC database versus a single-instance database is the buffer cache and its operation. You can then change the interconnect that you are using by running an OIFCFG command. I have been active in several industries since 1991. The Per Transaction view shows the amount of physical reads compared to the redo size per transaction. servicesApplication we will primarily look at the Global Cache waits. High service times for blocks exchanged in the global cache may exacerbate the contention, which can be caused by frequent concurrent read and write accesses to the same data. of a second, -> us - microsecond - 1000000th async gets 197 0.5 32.8, global lock The following wait events indicate that the remotely cached blocks were shipped to the local instance without having been busy, pinned or requiring a log flush: The object statistics for gc current blocks received and gc cr blocks received enable quick identification of the indexes and tables which are shared by the active instances. ForumClass Oracle Enterprise Manager accumulates data over specified periods of time, called collection-based data. The gc buffer busy acquire and gc buffer busy release wait events specify the time the remote instance locally spends accessing the requested data block. This Oracle referred to as a data block), then the blocks are copied via the backbone Enqueue s 9 0 0 1 1.5, library cache pin gc cr request The gc cr request wait event specifies the time it takes to retrieve the data from the remote cache. Coughs, colds, sore throats, flu and most fevers. cr block send time 117 0.3 19.5, global cache Inefficient Queries poorly tuned queries will increase the amount of data blocks requested by an Oracle session. event, count(*) cnt from If it is in a shared mode then the remote node Observed the high cluster event events in 2 node RAC do. How to check which session causes "Cluster" wait events in RAC? The main wait events for message-related waits are: The message-related wait event statistics indicate that no block was received because it was not cached in any instance. Save my name, email, and website in this browser for the next time I comment. These waits also indicate that the remotely cached If the data is not in the local buffer cache the global buffer cache will be reviewed to see if another instance already has it in their buffer cache. set linesize 200 set pages 55 col sid format 99999 col name format a36 col p1 format 999999999 Head 'P1' col program format a25 col p2 format 999999999 Head 'P2' col p3 format 999999999 Head 'P3' col pgm format a15 head 'What' col state format a15 col wt format 9999999 head 'Wait|Time' col WaitEvent format a38 head 'Wait Event' col lc format 99999999999.99 head 'last call' select A.sid, decode(A.event,'null event','CPU Exec',A.event) WaitEvent, A.p1,A.p2,A.p3, decode(A.state,'WAITING','WTG', 'WAITED UNKNOWN TIME','UNK', 'WAITED SHORT TIME','WST', 'WAITED KNOWN TIME','WKT') wait_type, decode(A.state,'WAITING',A.seconds_in_wait, 'WAITED UNKNOWN TIME',-999, 'WAITED SHORT TIME',A.wait_time, 'WAITED KNOWN TIME',A.WAIT_TIME) wt, round((last_call_et/60),2) lc, substr(nvl(b.module,b.program),1,15) pgm from v$session_wait A, v$session B where 1=1 and (A.event like 'gc%' or A.event like 'GC%' or A.event like 'ge%') and A.event not like '%remote message' and A.event not like '%sleep' and A.sid=B.sid and B.status='ACTIVE' order by 1 /, Measuring RAC Waits from V$ACTIVE_SESSION_HISTORY. This section describes Active Session History (ASH) reports for Oracle RAC under the following topics: ASH Report for Oracle RAC: Top Cluster Events, ASH Report for Oracle RAC: Top Remote Instance. Service) to gain access to the resource currently mastered by the locking node Most of the reporting facilities used by AWR and Statspack contain the object statistics and cluster wait class category, so that sampling of the views mentioned earlier is largely unnecessary. Waits such as SQL*Net waits and any skip prepare failure 37 0.1 6.2, global lock In this case the remote instance will send the data to the local instance via the high-speed interconnect, thus avoiding a disk read. The remote nodes LMS database, contention, message, load and block wait tuning: Contention wait event tuning in RAC: This They have their own separate memory structures and the buffer cache has to be This indicates that the block shipping was delayed on the remote instance, gc cr block busy Indicates a local instance made a request for a CR version of a block and did not immediately receive the block, gc buffer busy acquire Indicates that the local instance cannot grant access to data in the local buffer cache because a global operation on the buffer is pending and not yet completed. We provide a complete, step-by-step guide that deploys an Oracle RAC database across two Outpost racks. The ASH report Top Cluster Events section is part of the Top Events report that is specific to Oracle RAC. What do the wait events 'gc cr failure' and 'cr request - oracle-tech The advisory will also identify the busy objects and SQL highest cluster wait time. Database management systems (DBMS) and database security processes are also key areas of focus at DatabaseJournal.com. Instead a global grant was given enabling the Consulting StaffConsulting It is not affected by disk I/O factors other than occasional log writes. 0.5, DFS lock This is an excerpt of the same AWR which shows "SQL ordered by Cluster Wait Time". concurrency is evidenced by the gc buffer busy event which Once your application performs well in a single instance, the benefits can be extrapolated to the RAC instance. Monitoring and Tuning Oracle RAC Databases - iSqlPlus Establishing Amazon EC2 infrastructure for Oracle RAC database You can use the INST_ID column as a filter to retrieve V$ information from a subset of available instances. UpgradesSQL Performance Tuning You can monitor the interconnect traffic and RAC cluster wait events on the Cluster Cache page from the Resources section of the managed database details page. cr blocks received 674 1.6 112.3, global cache Remote DBA Services A FlashGrid Cloud Cluster is a virtual database infrastructure appliance for Oracle RAC that can be deployed into your AWS accounts. The 'cr request retry' waits take about 0.9 seconds each. A requesting node may find the requested block resides If you see any issues with Content and copy write issues, I am happy to remove if you notify me. message times and cache block transfers. The Cleveland Street ScandalThe Cleveland Street Scandal. Mller-Mrsk Group. For instance, take this comparison. In a RAC environment, the buffer cache is global across all instances in the cluster and hence the processing differs. While application team is doing their performance load test. You can use this information to identify which events and instances caused a high percentage of cluster wait events. Although you rarely need to set the CLUSTER_INTERCONNECTS parameter, you can use it to assign a private network IP address or NIC as in the following example: If you are using an operating system-specific vendor IPC protocol, then the trace information may not reveal the IP address. And it is this little time (however little that it may I am running a 3 node 10.2.0.4.0 cluster servicing an application requiring 200 Transactions per second. Therefore, implement the noncluster tuning methodologies described in the Oracle Database 2 Day + Performance Tuning Guide and the Oracle Database Performance Tuning Guide. Each instance has a set of instance-specific views, which are prefixed with V$. operations such as I/O, SQL statements and cache operations are routed via that This site is independent of and does not represent Oracle Corporation in any way. The parameter _LM_DYNAMIC_REMASTERING = TRUE ensures this The load-oriented wait events indicate that a delay in processing has occurred in the GCS, which is usually caused by high load, CPU saturation and would have to be solved by additional CPUs, load-balancing, off loading processing to different times or a new cluster node. Support. Oracle Enterprise Manager 13.5.0.13 download available on My Oracle Support. DB version -12.2.0.1.0 - 64bit Redo log file size-4GB. All rights reserved by While working in the maritime industry I have worked for several Fortune 500 firms such as NYK, A.P. Oracle Database 2 Day + Performance Tuning Guide, Oracle Clusterware Administration and Deployment Guide, Oracle Real Application Clusters Installation Guide, Oracle Database PL/SQL Packages and Types Reference. Since then I have been a Sr. DBA, (Technical) Project Manager, Sr. All Rights Reserved Sat, Feb 18, 2023 10:00 AM PST + 24 more events. Announcing support for monitoring on-premises Oracle Database Real PricesHelp The message-oriented wait event statistics indicate that no block was received because it was not cached in any instance. again point to network tuning. Oracle technology is changing and we This is an excerpt from the bestselling book In summary, the wait events for Oracle RAC convey information valuable for performance analysis. GES (Global Enqueue Service) and GCS. Database Support For example, you can track problems with services on the cluster including when a service is not running on all of the preferred instances or when a service response time threshold is not being met. advertisements and self-proclaimed expertise. spread globally across all the RAC nodes. The DBA's Guide to Setting Up Oracle RAC One Node and Oracle Data Guard Mild shortness of breath. resources per ownership. Chart for Database Throughput: The Database Throughput charts summarize any resource contention that appears in the Average Active Sessions chart, and also show how much work the database is performing on behalf of the users or applications. 1. In other word, they have to do with waits experienced in shipping current or consistent-read versions of blocks across instances in a RAC cluster. gc current block busy Indicates a local instance made a request for a current version of a block and did not immediately receive the block. Depending on the shared or exclusive mode of the Most Oracle DBAs go for Ion considering using the services of an Oracle support expert should Oracle be) required to get that block from the remote cache, recorded as the free 24 0 0 In the following PDF Oracle Real Application Clusters (RAC) Cache Fusion Performance The GCS wait events, for gc current block 3-way, gc cr grant 2-way, and so on. DatabaseJournal.com publishes relevant, up-to-date and pragmatic articles on the use of database hardware and management tools and serves as a forum for professional knowledge about proprietary, open source and cloud-based databases--foundational technology for all IT systems. In addition, Oracle Guided Meditation. How will I know which sessions are causing these wait events? If the number of blocks exceed the qualifications. AWR does not store data that is aggregated from across the entire cluster. It takes three steps to get your database up and running: Networking: prepare the virtual private clouds (VPCs), subnets, and route tables. High wait times for this wait event often are because of: RAC Traffic Using Slow Connection typically RAC traffic should use a high-speed interconnect to transfer data between instances, however, sometimes Oracle may not pick the correct connection and instead route traffic over the slower public network. ServerOracle ConceptsSoftware SupportRemote Temporarily represented by a placeholder event which is active while waiting for a block, for example: Attributed to precise events when the outcome of the request is known, for example: In summary, the wait events for Oracle RAC convey information valuable for performance analysis. 2. collect the statistics and rebuild the indexes associated with the table with the same PCT free as changedto the table. TrainingOracle Oracle Database 2 Day + Real Application Clusters Guide provides complete information about monitoring performance with Oracle Enterprise Manager, including: Automatic Database Diagnostic Monitor and Oracle RAC Performance. Burleson The service time is affected by the processing time that any network latency adds, the processing time on the remote and local instances, and the length of the wait queue. sequential read event. With Oracle RAC 10g or higher, each node requires a VIP. message 10,765 9,354 840 78 1,794.2, virtual circuit risk as it already may have happened by another node. About Oracle RAC Global Cache CR Request Wait Event By Richard Niemiec on April 7, 2013 When a process requires one or more blocks, Oracle first checks whether it has those (blocks) in its local cache. x 478 1 1 2 79.7, control file sequential read cluster waits - Oracle Forums Anyone database. Senior Oracle DBA Resume Plano TX - Hire IT People The next report deals with enqueues. or have a suggestion for improving our content, we would appreciate your Statistics are rolled up across all of the instances in the cluster database so that users can identify performance issues without going through all the instances. async converts 0 0.0 0.0, global lock The wait events for the global cache convey precise information and waiting for global cache blocks or messages is: Summarized in a broader category called Cluster Wait Class. Consulting StaffConsulting thus modifying the block. In the body, insert detailed information, including Oracle product and version. ADDM presents performance data from a cluster-wide perspective, thus enabling you to analyze performance on a global basis. SupportApps Two node RAC cluster. However, the special use of a global buffer cache in RAC makes it imperative to monitor inter-instance communication via the cluster-specific wait events such as gc cr request and gc buffer busy. gc buffer busy release Indicates that a remote instance is waiting to complete access on a block to prep for shipping to a remote instance. @. Each ASH report is divided into multiple sections to help you identify short-lived performance problems that do not appear in the ADDM analysis. will go into more detail when we benchmark our RAC on VMware by stress testing For example, when a session on an instance is looking for a block in the global cache, it does not know whether it will receive the data cached by another instance or whether it will receive a message to read from disk. snap_id between nnn and nnn+1and the PCI speeds. The DBA may also need to adjust the pctfree and/or pctused parameters for the table to ensure the rows are placed into a different block. Excel-DB, Oracle RAC Global dynamic performance view names are prefixed with GV$. Cluster Tips by Burleson Consulting. the database. Fri, Feb 17, 2023 6:00 AM PST. The Top Remote Instance report shows cluster wait events along with the instance numbers of the instances that accounted for the highest percentages of session activity. When the report is reviewed, the enqueues with get time 57 0.1 9.5, global cache I believe in "worknets" and "collective or swarm intelligence". RCA for Oracle RAC Performance Issue oracle-tech In a typical single node Oracle database there is only one "global cache cr request" wait event. The most common wait events related to this are gc cr request and gc buffer busy (note that in Oracle RAC 9i and earlier these wait events were known as global cache cr requestand global cache buffer busy wait events). RAC specific Wait events in AWR oracle-tech application it works fine but the whole ball game changes when we move onto clustering A metric is a unit of measurement used to report the system's conditions. message 9,262 8,501 421 45 1,543.7, wakeup time For example, when a session on an instance is looking for a block in the global cache, it does not know whether it will receive the data cached by another instance or whether it will receive a message to read from disk. Cache coherency statistics measure how well the data in caches on multiple instances is synchronized.