RAC

Quiescing RAC Databases To quiesce a RAC database, use the ALTER SYSTEM QUIESCE RESTRICTED statement from one instance. It is not possible to open the database from any instance while the database is in the process of being quiesced from another instance. After all the non-DBA sessions become inactive, the ALTER SYSTEM QUIESCE RESTRICTED statement executes and the database is considered to be quiesced. In RAC, this statement affects all instances. SQL> ALTER SYSTEM QUIESCE RESTRICTED; To … [Read more...] about How to quiesce an Oracle 12c RAC database

Starting and Stopping RAC Instances In a RAC environment, multiple instances can have the same RAC database open at the same time. The procedures for starting up and shutting down RAC instances are identical to the procedures used in single-instance Oracle, with the following exception: - The SHUTDOWN TRANSACTIONAL command with the LOCAL option is useful to shut down an instance after all active transactions on the instance have either committed or rolled back. Transactions on other … [Read more...] about How to Start and Stop Oracle RAC Instances (CDB/PDB)

Local Temporary Tablespaces To improve I/O operations, Oracle introduces a local temporary tablespace in Oracle Database 12c release 2 (12.2), so that spill-overs are written to the local disks on the reader nodes. It is still possible for SQL operations, such as hash aggregation, sort, hash join, creation of cursor-duration temporary tables for the WITH clause, and star transformation to spill over to disk (specifically to the global temporary tablespace on shared disks). Management of the … [Read more...] about Oracle Database 12c New feature: Local Temporary Tablespaces

The Oracle database automatically manages undo segments within a specific undo tablespace that is assigned to an instance. Under normal circumstances, only the instance assigned to the undo tablespace can modify the contents of that tablespace. However, all instances can always read all undo blocks for consistent-read purposes. Also, any instance can update any undo tablespace during transaction recovery, as long as that undo tablespace is not currently used by another instance for undo … [Read more...] about Automatic Undo Management and Oracle RAC

Redo Log Files and RAC In an Oracle RAC database, each instance must have at least two groups of redo log files. You must allocate the redo log groups before enabling a new instance with the ALTER DATABASE ENABLE INSTANCE instance_name command. When you use DBCA to create the database, DBCA allocates redo log files to instances, as required, automatically. You can change the number of redo log groups and the size of the redo log files as required either during the initial database creation or … [Read more...] about Define redo log files in an Oracle RAC environment

Separation of Duty for Administering Oracle Real Application Clusters. Starting with Oracle Database 12c Release 2, Oracle Database provides support for separation of duty best practices when administering Oracle RAC by introducing the SYSRAC administrative privilege for the clusterware agent. This feature removes the need to use the powerful SYSDBA administrative privilege for Oracle RAC. SYSRAC, like SYSDG, SYSBACKUP and SYSKM, helps enforce separation of duties and reduce reliance on the … [Read more...] about Oracle Database 12c New Feature: SYSRAC administrative privilege

Starting with Oracle Grid Infrastructure 12c Release 2, it is now possible to run read-only instances on Leaf nodes. Oracle Grid Infrastructure 12c introduced the concept of Oracle Flex cluster in which nodes can be classified as a Hub node or a Leaf node. In Oracle Grid Infrastructure12c Release 1, database instances could only be installed on Hub nodes and Leaf nodes were used to host applications. Starting with Oracle Grid Infrastructure 12c Release 2, it is now possible to run read-only … [Read more...] about Oracle Grid 12c: Read Only Instances on Leaf Nodes

An Oracle RAC database has the same processes and memory structures as a single-instance Oracle database and 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. The Oracle RAC processes and their identifiers are as follows: ACMS Atomic Control File to Memory Service GTX[0-j] Global Transaction Process LMON Global Enqueue Service … [Read more...] about Background Processes Specific to Oracle RAC

Oracle Net Services Overview Oracle Net Services provide enterprise-wide connectivity solutions in distributed, heterogeneous computing environments. It enables a network session from a client application to an Oracle Database server. A dedicated server process is a type of service handler that the listener starts when it receives a client request. The slide depicts the process of establishing a connection from a client to an Oracle Database (non-shared server architecture) by using … [Read more...] about Basics of client connectivity in Oracle Data Guard configuration