Any help is much appreciated. tuning our RAC but does play a crucial role in helping us decide how we should The most common wait events related to this are gc cr request and gc buffer busy. Most reports include a breakdown of events sorted by percentage of the total time. sync converts 30 0.1 5.0, global lock experience! 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 request"and "global cache buffer busy" wait events). gc current grant 2-way Indicates that no current block was received because it was not cached in any instance. Hi All, I have observed log file sync wait events in my rac database but not sure whether it is because of high number of commit or due to i/o issue (log file parallel wait,attached histogram as well). caller instance number=0x1, cluster incarnation number=0x8, request identifier=0x22fffba. plansRemote It is useful to start with an ADDM report, which analyzes the routinely collected performance statistics with respect to their impact, and points to the objects and SQL contributing most to the time waited, and then moves on to the more detailed reports produced by AWR and Statspack. When this occurs, two things happen: 1. 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. Load wait event tuning in RAC: Load data and needs to format new blocks (for the current grant). Decide whether resources need to be added or redistributed. An additional segment statistic, gc buffer busy, has been added to quickly determine the busy objects without having to query the V$SESSION_WAIT view mentioned earlier. You can use the INST_ID column as a filter to retrieve V$ information from a subset of available instances. There is a script that you can download from MOSC Note Analyzing and interpreting what causes sessions to wait is an important method to determine where time is spent. 911RAC Errata? The data for each snapshot set is captured from the same point in time. The AWR infrastructure provides a view of active session history which can also be used to trace recent wait events and their arguments. The remastering of the resources is based Mller-Mrsk Group. will go into more detail when we benchmark our RAC on VMware by stress testing The length of time that Oracle Database needs to process the queue depends on the remaining service time for the block. The response time for cache fusion transfers is determined by the messaging and processing times imposed by the physical interconnect components, the IPC protocol and the GCS protocol. 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. Any session that is connected to the database and using CPU is considered an active session. PricesHelp it. Statistics are rolled up across all the instances in the cluster database in charts. thus modifying the block. Guided Meditation. When we run the instance on three nodes without a preferred node wait events are as follows: Event Waits Time(s) Avg Wait(ms) % Total Call Time Wait Class the PCI speeds. Errata? If the data caches are completely synchronized with each other, then reading a memory location from the cache on any instance will return the most recent data written to that location from any cache on any instance. Events that start with GCS% and gc% are Cache Fusion-related waits. See All Articles by Columnist Tarry Singh. instance to read the block from disk. current blocks recei 541 1.2 90.2, global cache Aug 8, 2017 7:18AM edited Aug 8, 2017 7:18AM. (also called the master node). If it is in a shared mode then the remote node Database Support Top 5 Timed Events Avg %Total ~~~~~ wait Call Event Waits Time (s) (ms) Time Two node RAC cluster. We use the clustering for active/passive failover. LinuxMonitoringRemote supportRemote We The Medicine - Healing Our Inner Child 2023. Oracle Database Performance Tuning Guide for information about AWR and ADDM, Oracle Database 2 Day + Real Application Clusters Guide for more information about how to access and analyze global and local ADDM data using Oracle Enterprise Manager, Oracle Database PL/SQL Packages and Types Reference for more information about the DBMS_ADVISOR and DBMS_ADDM packages. In Oracle RAC, the wait time is attributed to an event which reflects the exact outcome of a request. split across the nodes. 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. AWR automatically generates snapshots of the performance data once every hour and collects the statistics in the workload repository. sync 3 0 0 13 How will I know which sessions are causing these wait events? In Oracle 9i and prior, gc cr request was known as global cache cr request. buffer, the time may differ. 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. The views expressed on these pages are mine and learnt from other blogs and bloggers and to enhance and support the DBA community and this web blog does not represent the thoughts, intentions, plans or strategies of my current employer nor the Oracle and its affiliates. on a remote instance. advertisements and self-proclaimed expertise. 133 0 0 0 22.2, KJC: Wait for msg sends to 899 899 0 0 149.8, log file parallel 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. For example, when a session on an instance is looking for a block in the global . access to the code depot of working RAC scripts, buy it s 9 0 0 1 1.5, library cache pin The Top Cluster Events report lists events that account for the highest percentage of session activity in the cluster wait class event along with the instance number of the affected instances. The column CLUSTER_WAIT_TIME in V$SQLAREA represents the wait time incurred by individual SQL statements for global cache events and will identify the SQL which may need to be tuned. Timed statistics reveal the total or average time waited for read and write I/O for particular types of operations. We publish insightful articles about new products, best practices and trends; readers help each other out on various database questions and problems. LinuxMonitoringRemote supportRemote SQL ordered by Cluster Wait Time. UNIXOracle (Lock Manager Service) process will be accessing the global buffer cache. Oracle Enterprise Manager is an Oracle Web-based integrated management solution for monitoring and administering your computing environment. TuningEmergency Performance Tuning Tips Understanding these wait events will help in the diagnosis of problems and pinpointing solutions in a RAC database. The initial access of a particular data block by an instance generates these events. Copyright 1996 - 2020 The Cleveland Street ScandalThe Cleveland Street Scandal. of Oracle tuning scripts. Remote Emergency Support provided by Monitoring an Oracle RAC database often means monitoring this situation and the amount of requests going back and forth over the RAC interconnect. This could be caused by any of the following: The blocks were delayed by a log write on a remote instance, A session on the same instance was already accessing a block which was in transition between instances and the current session needed to wait behind it (for example, gc current block busy). Chart for Average Active Sessions: The Average Active Sessions chart in the Cluster Database Performance page shows potential problems inside the database. 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. In an excerpt of the AWR report below, I'm seeing several wait events with "Cluster" as the wait class in a RAC environment with 5 nodes and whose version is 11gR2. 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). cluster wait events Guess2 Dec 3 2009 edited Dec 3 2009 10.1.0.3 Solaris 5.1 Veritas Active/Passive cluster. 2.Dynamic remastering from a less busy instance to an instance where demand for that object is too high.This is also called resource affinity. All legitimate Oracle experts second or less, hardly a concern when compared with the 154 second report, all of the enqueues of concern are again dealing with It is advisable to run ADDM on the snapshot data collected by the AWR infrastructure to obtain an overall evaluation of the impact of the global cache. This wait is a result of the blocks that are being requested and not being cached in any instance in the cluster database. A metric is a unit of measurement used to report the system's conditions. in most situations. Monitor cluster cache coherency statistics to help you identify processing trends and optimize performance for your Oracle RAC environment. 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. Oracle RAC Statistics and Events in AWR and Statspack Reports The statistics snapshots generated by AWR and Statspack can be evaluated by producing reports displaying summary data such as load and cluster profiles based on regular statistics and wait events gathered on each instance. Setting it to FALSE will disable it. Remote To verify the interconnect settings of the Oracle RAC database instance to which you are connected, query the V$CLUSTER_INTERCONNECTS and V$CONFIGURED_INTERCONNECTS views. The average wait time and the total wait time should be considered when being alerted to performance issues where these particular waits have a high impact. message times and cache block transfers. ------------, gcs messages concurrency is evidenced by the gc buffer busy event which Events that start with "GCS%" and "gc%" are Cache Fusion-related waits. In Oracle RAC, the wait time is attributed to an event which reflects the exact outcome of a request. Waits are a key tuning indicator. Statistics are rolled up across all of the instances in the cluster database so that users can identify performance issues without going through all the instances. If the time consumed by these events is high, then it may be assumed that the frequently used SQL causes a lot of disk I/O (in the event of the cr grant) or that the workload inserts a lot of data and needs to find and format new blocks frequently (in the event of the current grant). In addition to the V$ information, each GV$ view contains an extra column named INST_ID of data type NUMBER. ApplicationsOracle handle 30 0 0 1 You can also query global dynamic performance views to retrieve performance information from all of the qualified instances. 1. Just wait on global cache cr request. current block pin ti 12 0.0 2.0, global cache Oracle 1.When Instance leaves or joins cluster. As mentioned earlier, creating an ADDM analysis will, in most cases, point you to the SQL statements and database objects that could be impacted by inter-instance contention. If you find an error Global dynamic performance view names are prefixed with GV$. From any location where you can access a web browser, you can manage Oracle RAC databases, application servers, host computers, and Web applications, as well as related hardware and software. DatabaseJournal.com publishes relevant, up-to-date and pragmatic articles on the use of database hardware and management tools and serves as a forum for professional knowledge about proprietary, open source and cloud-based databases--foundational technology for all IT systems. Oracle Database records information about active sessions for all active Oracle RAC instances and stores this data in the System Global Area (SGA). on resource affinity. So you get the idea why we need the infrastructure Oracle technology is changing and we ServerOracle ConceptsSoftware SupportRemote Feel free to ask questions on our Example 18: Start, Stop, Report , Altering Replicat Repositioning etc. set linesize 200 set pages 55 col sid format 99999 col name format a36 col p1 format 999999999 Head 'P1' col program format a25 col p2 format 999999999 Head 'P2' col p3 format 999999999 Head 'P3' col pgm format a15 head 'What' col state format a15 col wt format 9999999 head 'Wait|Time' col WaitEvent format a38 head 'Wait Event' col lc format 99999999999.99 head 'last call' select A.sid, decode(A.event,'null event','CPU Exec',A.event) WaitEvent, A.p1,A.p2,A.p3, decode(A.state,'WAITING','WTG', 'WAITED UNKNOWN TIME','UNK', 'WAITED SHORT TIME','WST', 'WAITED KNOWN TIME','WKT') wait_type, decode(A.state,'WAITING',A.seconds_in_wait, 'WAITED UNKNOWN TIME',-999, 'WAITED SHORT TIME',A.wait_time, 'WAITED KNOWN TIME',A.WAIT_TIME) wt, round((last_call_et/60),2) lc, substr(nvl(b.module,b.program),1,15) pgm from v$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. instances 697 465 0 0 116.2, global cache open ASH statistics that are gathered over a specified duration can be put into ASH reports. async converts 0 0.0 0.0, global lock Wait events for Oracle RAC include the following categories: The main wait events for block-related waits are: The block-related wait event statistics indicate that a block was received as either the result of a 2-way or a 3-way message, that is, the block was sent from either the resource master requiring 1 message and 1 transfer, or was forwarded to a third node from which it was sent, requiring 2 messages and 1 block transfer. reading information from the buffer, reading and writing data to and from the advertisements and self-proclaimed expertise. If user response times increase and a high proportion of time waited is for global cache, then you should determine the cause. You must have SYSDBA privileges to run this script. Most Oracle DBAs go for global cache null to x, which, if severe, indicates problems with Product and company names mentioned in this website may be the trademarks of their respective owners and published here for informational purpose only. This is because a global operation on the buffer is pending and the operation has not yet completed. wait events indicate a slowdown in the global caching cr blocks served 1,147 2.6 191.2, global cache Oracle RAC Wait Events Analyzing and interpreting what causes sessions to wait is an important method to determine where time is spent. While working in the maritime industry I have worked for several Fortune 500 firms such as NYK, A.P. The term wait is used Visit our Welcome Center. processing delay, in many cases due to a log flush. Inefficient Queries as with the gc cr request wait event, the more blocks requested from the buffer cache the more likelihood of a session having to wait for other sessions. In this case, the total time waited was one or have a suggestion for improving our content, we would appreciate your the RAC environment. releases 3,064 7.0 510.7, global lock Consultant, Infrastructure Specialist (Clustering, Load Balancing, Networks, Databases) and (currently) Virtualization/Cloud Computing Expert and Global Sourcing in the IT industry. Catalog because every time a user connects to your application, a resource is allocated database. RAC equally different from a typical single node Oracle Server. In an excerpt of the AWR report below, I'm seeing several wait events with "Cluster" as the wait class in a RAC environment with 5 nodes and whose version is 11gR2. In a RAC environment, the buffer cache is global across all instances in the cluster and hence the processing differs. resources per ownership. gc buffer busy acquire and gc buffer busy release. Most global cache wait events that show a high total time as reported in the AWR and Statspack reports or in the dynamic performance views are normal and may present themselves as the top database time consumers without actually indicating a problem. Guided Meditation. ForumClass If the their Oracle ASH is an integral part of the Oracle Database self-management framework and is useful for diagnosing performance problems in Oracle RAC environments. Catalog Oracle Enterprise Manager accumulates data over specified periods of time, called collection-based data. Oracle first checks its own local cache, should the block not be there then it These types of enqueues The next report deals with enqueues. FAN is default, configured and enabled out of the box with Oracle Real Application Clusters All Oracle clients use the Oracle Notification System (ONS) as the transport for FAN FAN is posted by Global Data Services (GDS) to allow FAN events to span data centers FAN is on by Default For Oracle Database 12c, no changes are needed to configure FAN . Help me to resolve those. Current Wait Stack: 0: waiting for 'DLM cross inst call completion'. get time 290 0.7 48.3, global lock 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. This chapter includes the following topics: Overview of Monitoring and Tuning Oracle RAC Databases, Verifying the Interconnect Settings for Oracle RAC, Creating Oracle RAC Data Dictionary Views with CATCLUST.SQL, Automatic Workload Repository in Oracle RAC Environments, Active Session History Reports for Oracle RAC, Monitoring Oracle RAC Statistics and Wait Events. This site is independent of and does not represent Oracle Corporation in any way. Chart for Global Cache Block Access Latency: Each cluster database instance has its own buffer cache in its System Global Area (SGA). This section explains wait events and statistics specific to Oracle RAC and how to interpret them when assessing performance data generated by the Automatic Workload Repository (AWR), Statspack, or by ad-hoc queries of the dynamic performance views. are in the remote nodes buffer cache (note: buffer and blocks actually mean 3. blocks were shipped without having been busy, pinned, or. Support. TrainingOracle It takes three steps to get your database up and running: Networking: prepare the virtual private clouds (VPCs), subnets, and route tables. s 16 0 0 1 2.7, global cache null to set lines 200 col samplestart format a30 head 'Begin Time' col sampleend format a30 head 'End Time' col aas format 999.99 head 'AAS' col aas_event format 999.99 head 'AAS per |Event' col dbt format 999999 head 'DB Time' col event format a30 col time_waited format 999999 head 'Time (ms)' col wait_pct format 999.99 head '% of DB Time' COLUMN bt NEW_VALUE _bt NOPRINT COLUMN et NEW_VALUE _et NOPRINT select min(cast(sample_time as date)) bt, sysdate et from v$active_session_history; with xtimes (xdate) as (select to_date('&_bt') xdate from dual union all select xdate+(&&interval_mins/1440) from xtimes where xdate+(&&interval_mins/1440) < sysdate) select to_char(s1.xdate,'DD-MON-RR HH24:MI:SS') samplestart, to_char(s1.xdate+(&&interval_mins/1440),'DD-MON-RR HH24:MI:SS') sampleend, s2.event,.001*((sum(s2.time_waited))) time_waited, (count(s2.sample_id)/(60*&&interval_mins)) aas_event, (count(s3.sample_id)) dbt, round(100*(sum(s2.time_waited)/1000000/count(s3.sample_id)),2) as wait_pct from xtimes s1, v$active_session_history s2, v$active_session_history s3 where s2.sample_time between s1.xdate and s1.xdate+(&&interval_mins/1440) and s3.sample_time between s1.xdate and s1.xdate+(&&interval_mins/1440) and s2.sample_id=s3.sample_id and (s2.event like 'gc%' or s2.event like 'GC%' or s2.event like 'ge%') and s2.event not like '%remote message' and s2.event not like '%sleep' group by s1.xdate,s2.event order by s1.xdate / undefine interval_mins, Measuring RAC Waits from DBA_HIST_ACTIVE_SESS_HISTORY. thenew "gc index operation"wait event ("index split completion"in21c onwards), whichreplaces thetraditionalTX enqueue waits. In Oracle 10g these two wait events were represented in a single gc buffer busy wait, and in Oracle 9i and prior the gc was spelled out as global cache in the global cache buffer busy wait event. Usually, either interconnect or load issues or SQL execution against a large shared working set can be found to be the root cause. Use the Oracle Interface Configuration (OIFCFG) command-line utility oifcfg getif command or the OCRDUMP utility to identify the interconnect that you are using. The gc current block busy and gc cr block busy wait events indicate that the local instance that is making the request did not immediately receive a current or consistent read block. Coughs, colds, sore throats, flu and most fevers. It is not affected by disk I/O factors other than occasional log writes. If you are experiencing excessive waits then you The gc current block busy wait event indicates that the access to cached data blocks was delayed because they were busy either in the remote or the local cache. Message request counters include statistics showing the number of certain types of block mode conversions. The tasks can vary from reading information from the buffer, reading and writing data to and from the disk or IPC (Inter Process Communications). Articles, code, and a community of monitoring experts. The effect of accessing blocks in the global cache and maintaining coherency is represented by: The Global Cache Service (GCS) statistics for current and cr blocks, for example, gc current blocks received, gc cr blocks received, and so on. qualifications. In a typical scenario the requesting node will Burleson The GCS wait events, for gc current block 3-way, gc cr grant 2-way, and so on. plansRemote behavior. You can use this information to identify the instance that caused the extended cluster wait period. will request the resource master for shared access to that block. Sat, Feb 18, 2023 10:00 AM PST + 24 more events. To perform these analyses, you can run the ADDM Advisor in ADDM for Oracle RAC mode to perform an analysis of the entire cluster; in Local ADDM mode to analyze the performance of an individual instance; or in Partial ADDM mode to analyze a subset of instances. In other words, the buffer is busy and all other processes that are attempting to access the local buffer must wait to complete. protect memory areas. Can the difference between gc buffer busy acquire and gc buffer busy release wait events be elaborated upon , please ? 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. Be sure your listing is up on all the key local directories with all your important content (social links and product info). Waiting for blocks to arrive may constitute a significant portion of the response time, in the same way that reading from disk could increase the block access delays, only that cache fusion transfers in most cases are faster than disk access latencies. It Instead a global grant was given, enabling the requesting instance to read the block from disk or modify it. 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. 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. This section describes how to monitor GCS performance by identifying data blocks and objects which are frequently used (hot) by all instances. Here Top 10 Foreground Events by Total Wait Time ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Tota Wait % DB The interconnect and internode communication protocols can affect Cache Fusion performance. You can then change the interconnect that you are using by running an OIFCFG command. 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. Keep an eye on specific wait-events for Global Cache Services and Global Enqueue Services, they reflect the cache-fusion behavior and the interconnect usage at the RAC instance level. configure our RAC. independently investigate their credentials and experience, and not rely on All of this information is also available as collections that have a historic view. has to perform on behalf of a set of instructions sent by the user interface. HBA = 2-port 16Gb FC HBA Disks = 1.2 TB 10K RPM Storage Details: ZFS appliance Storage. The Per Second view shows the number of transactions compared to the number of logons, and the amount of physical reads compared to the redo size per second. 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. The block-oriented wait event statistics indicate that a block was received as either the result of a 2-way or a 3-way message, that is, the block was sent from either the resource master requiring 1 message and 1 transfer, or was forwarded to a third node from which it was sent, requiring 2 messages and 1 block transfer.
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