Storage and Compute Node Communication

The storage tier in Exadata is not only providing the feature of persistent storage or alternatively its capability is not only limited to storing the data rather than the storage tier in Exadata is very well aware about database architecture and it also has the capability to filter out the data at the storage level so that only the required set of data will be transferred to the compute node which eventually provide the benefit of extreme database performance, however we still need to understand how the data transfer initiates and how it moves between storage tier and compute node and vice-versa.

                      Stages of query processing or data transfer

STAGE 1: Query Execution

When the query got executed at compute node, the database sends the query plan to the storage tier using InfiniBand switches or ROCE switches vary from version to version of Exadata.

STAGE 2: Query Processing

Once the storage tier receives the query plan sent by the database server and determine what data need to be retrieved and it then initiates the data transfer request using iDB protocol.

STAGE 3: Data Transfer

The data transfer will happen directly between storage tier and the compute node using RDMA protocol using either InfiniBand switch or ROCE switch.

STATE 4: Query Completion

Once the data will be received by the compute node, it then transfers the query’s data to the application user.

                   Benefit provided at Exadata storage tier

Smart Scan: The feature of smart scan which filter out the require set of data will be provide at storage tier level which help in boosting the data transfer speed by mitigating the traffic of unnecessary data transfer.

High Speed Data Transfer Rate: Exadata provide the benefit of using either InfiniBand or ROCE switch which helps to provide ultra-fast speed to transfer the data from storage tier to compute node and it ranges from 40 GB/sec in InfiniBand and up to 100 GB/sec while using ROCE switch.

Use Of iDB protocol: iDB protocol is specifically designed for oracle Exadata which helps in optimizing the data transfer by reducing the number of round trips and efficiently packing data into infiniband packet.

RDMA: RDMA protocol helps to boost the performance by providing the feature of memory-to-memory transfer which ultimately mitigate the cpu involvement at compute node and less involvement of the cpu cycle means the more and more usage of resources for further activity at compute node level.

                                Who manages the IO request

CELLSRV: cellsrv process is the core component of storage tier which help in handing the I/O request from compute node, managing storage resources and executing smart scan operations.

IORM: IORM stands for I/O resource manager, in Exadata storage tier IORM helps in prioritizing and distributing the resources for handing the I/O request to get the maximum performance benefit.