Fast Application Notification [FAN] overview

As the Oracle docs say, The Oracle RAC, FAN, Oracle 12c Fast Application Notification (FAN) feature provides a simplified API for accessing FAN events through a callback mechanism. This mechanism enables third-party drivers, connection pools, and containers to subscribe, receive and process FAN events. These APIs are referred to as Oracle RAC FAN APIs. If […]

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Grid Naming Service in Oracle RAC

When we use Oracle RAC, all clients must be able to reach the database. All public addresses, VIP addresses and SCAN addresses of Cluster must be resolved by the clients.And GNS[Grid Naming Service] helps us resolve this problem. GNS is linked to the domain name server (DNS) so that clients can resolve these dynamic addresses […]

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Miscellaneous Oracle RAC wait events

Miscellaneous Oracle RAC wait events 1. gc remaster : resource remastering happens based on 2 situation : 1.When Instance leaves or joins 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. 2. gc cr grant busy : The gc cr […]

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Rebootless node fencing in Oracle RAC

Oracle Grid Infrastructure 11.2.0.2 has many features including Cluster Node Membership, Cluster Resource Management, and Cluster Resources monitoring. One of the key areas where DBA need to have expert knowledge on how the cluster node membership works and how the cluster decides to take out node should there be a heartbeat network, voting disk or […]

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Node eviction in Oracle RAC

Node eviction is quite sometimes happening in Oracle RAC environment on any platform and troubleshooting and finding root cause for node eviction is very important for DBAs to avoid same in the future. There can be many reasons behind node eviction like , Network Heartbeat Missed Voting Heartbeat Missed CSSD Agent/ Monitor hung RDBMS instance […]

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Split Brain and Amnesia in Oracle RAC

Split Brain and Amnesia Two types of problems can arise from cluster partitions: split brain and amnesia. Split brain occurs when the cluster interconnect between hosts is lost and the cluster becomes partitioned into subclusters, and each subcluster believes that it is the only partition. A sub-cluster that is not aware of the other subclusters […]

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Oracle RAC Cache Fusion

Cache Fusion is one of the most Important concepts in Oracle RAC. As we know each and every instance of RAC cluster is having its own local buffer cache where it does cache functionality.But when multiple users are connected to different nodes , a need to access or lock a data block owned by other […]

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How GRD works in Oracle RAC

An Oracle RAC database has the same processes and memory structures as a single instance.Oracle database have additional process and memory structures that are specific to Oracle RAC.The global cache service and global enqueue service processes, and the global resource directory (GRD) collaborate to enable cache fusion. Global Resource Directory [GRD] : Cluster operations require […]

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Downgrading Grid Infrastructure from 12.1.0.2 to 11.2.0.4

In the last article, we performed downgrade of Oracle RAC Database from 12c to 11gR2. In this article, we are going to downgrade Oracle Grid Infrastructure from 12c (12.1.0.2) to 11gR2 (11.2.0.4) which contains two nodes ( node 1 & node 2). Before doing CRS downgrade we need to take backup of following files : Take tar […]

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Downgrading a RAC database from 12.1.0.2 to 11.2.0.4

In the last article, we performed downgrade of Oracle Standalone Database from 12c to 11gR2. In this article, we can downgrade the 2 node RAC 12.1.0.2 database to 11.2.0.4, downgraded the database only and not the grid home. Assume all commands are being run on node 1, any commands that need to be run on node 2 […]

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