How does RAC cache fusion work in Oracle?

Cache fusion writes occur when a block previously changed by another instance needs to be written to disk in response to a checkpoint or cache aging. When this occurs, Oracle sends a message to notify the other instance that a fusion write will be performed to move the data block to disk.

What is Cache Fusion and cache coherence in Oracle RAC?

Cache Coherency demands that even though there are multiple instances (each with a separate db_cache_size data buffer region) in which data blocks can reside or brought in, block consistency must be maintained. Oracle RAC achieves this by following the inter-instance block transfers through Cache Fusion mechanism.

Which process is responsible for cache fusion?

Cache Fusion is implemented by a controlling mechanism called Global Cache Service[GCS]. And yes, to maintain the integrity of data is a task of GCS. We can say that GCS is a heart of CACHE FUSION process. GCS is available in RAC as LMS background process.

What is Cache Fusion and how does this affect applications?

Cache Fusion uses a high-speed IPC interconnect to provide cache-to-cache transfers of data blocks between instances in a cluster. This data-block shipping eliminates the disk I/O and optimizes read/write concurrency.”

What is split brain in RAC?

Split Brain is often used to describe the scenario when two or more nodes in a cluster, lose connectivity with one another but then continue to operate independently of each other, including acquiring logical or physical resources, under the incorrect assumption that the other process(es) are no longer operational or …

What is scan listener in Oracle RAC?

Single Client Access Name (SCAN) is an Oracle Real Application Clusters (Oracle RAC) feature that provides a single name for clients to access Oracle Databases running in a cluster. The benefit is that SCAN-NAME you provide for client connection is enough to connect to your database in RAC cluster.

What is split brain syndrome in RAC?

Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect, Although the servers are physically up and running and the database instances on these servers is also running.

What do you understand by Cache Fusion?

Cache Fusion is a new technology that uses a high speed interprocess communication (IPC) interconnect to provide cache to cache transfers of data blocks between instances in a cluster. This eliminates disk I/O (which is inherently slow, since it is a mechanical process) and optimizes read/write concurrency.

What is GES and GCS in Oracle RAC?

Global Cache Service (GCS) and Global Enqueue Service (GES) GCS and GES (which are basically RAC processes) play the key role in implementing Cache Fusion. GCS ensures a single system image of the data even though the data is accessed by multiple instances.

What is GCS and GES in RAC?

Why are there 3 scan listener in Oracle RAC?

SCAN provides location independence for the databases. Allow clients to use EZConnect or JDBC connections. SCAN Listener would forward the request to local listener that’s running on VIPs. Each cluster will have 3 SCAN listeners, each having a SCAN VIP defined as cluster resources.

How does Cache Fusion work in my Oracle?

Cache Fusion Oracle RAC transfer the data block from buffer cache of one instance to the buffer cache of another instance using the cluster high speed interconnect. For instance, Instance A read the block and it is in local buffer cache.

What is the concept of Cache Fusion in RAC?

This concept is known as CACHE FUSION where one instance can work on or access a data block in other instance’s cache via the high speed interconnect. Cache Fusion architecture helps resolve each possible type of contentions that could be thought of in a multi-node RAC setup.

How did Oracle use disk pinging before RAC fusion?

Oracle used disk pinging Prior to Oracle RAC Cache Fusion concept. There was no data block transfer between the buffer cache of one instance buffer cache of another instance.

Do you need a shared cache for Oracle RAC?

In order to facilitate Cache Fusion, we still need the Buffer Cache, the Shared Pool and the Undo tablespace just like a single-instance database. However, for Oracle RAC, we need the Buffer Caches on all instances to appear to be global across the cluster.