For mission critical systems, you must be able to perform failover and recovery, and your environment must be resilient to all types of failures.

For mission critical systems, you must be able to perform failover and recovery, and your environment must be resilient to all types of failures. To reach these goals, start by defining service level requirements for your business. The requirements should include definitions of maximum transaction response time and recovery expectations for failures within the data center (such as for node failure) or for disaster recovery (if the entire data center fails). Typically, the service level objective is a target response time for work, regardless of failures. Determine the recovery time for each redundant component. Even though you may have hardware components that are running in an active/active mode, do not assume that if one component fails the other hardware components can remain operational while the faulty components are being repaired. Also, when components are running in active/passive mode, perform regular tests to validate the failover time. For example, recovery times for storage channels can take minutes. Ensure that the outage times are within your business' service level agreements, and where they are not, work with the hardware vendor to tune the configuration and settings.

When deploying mission critical systems, the testing should include functional testing, destructive testing, and performance testing. Destructive testing includes the injection of various faults in the system to test the recovery and to make sure it satisfies the service level requirements. Destructive testing also allows the creation of operational procedures for the production system.

To help you design and implement a mission critical or highly available system, Oracle provides a range of solutions for every organization regardless of size. Small work groups and global enterprises alike are able to extend the reach of their critical business applications. With Oracle and the Internet, applications and their data are now reliably accessible everywhere, at any time. The Oracle Maximum Availability Architecture (MAA) is the Oracle best practices blueprint that is based on proven Oracle high availability technologies and recommendations. The goal of the MAA is to remove the complexity in designing an optimal high availability architecture.

Applications can take advantage of many Oracle Database, Oracle Clusterware, and Oracle RAC features and capabilities to minimize or mask any failure in the Oracle RAC environment. For example, you can:

• Remove TCP/IP timeout waits by using the VIP address to connect to the database.

• Create detailed operational procedures and ensure you have the appropriate support contracts in place to match defined service levels for all components in the infrastructure.

• Take advantage of the Oracle RAC Automatic Workload Management features such as connect time failover, Fast Connection Failover, Fast Application Notification, and the Load Balancing Advisory.

• Place voting disks on separate volume groups to mitigate outages due to slow I/O throughput. To survive the failure of x voting devices, configure 2x + 1 mirrors.

• Use Oracle Database Quality of Service Management (Oracle Database QoS Management) to monitor your system and detect performance bottlenecks.

• Place OCR with I/O service times in the order of 2 milliseconds (ms) or less.

• Tune database recovery using the FAST_START_MTTR_TARGET initialization parameter.

• Use Oracle Automatic Storage Management (Oracle ASM) to manage database storage.

• Ensure that strong change control procedures are in place.

• Check the surrounding infrastructure for high availability and resiliency, such as LDAP, NIS, and DNS. These entities affect the availability of your Oracle RAC database. If possible, perform a local backup procedure routinely.

• Use Oracle Enterprise Manager to administer your entire Oracle RAC environment, not just the Oracle RAC database. Use Oracle Enterprise Manager to create and modify services, and to start and stop the cluster database instances and the cluster database.

• Use Recovery Manager (RMAN) to back up, restore, and recover data files, control files, server parameter files (SPFILEs) and archived redo log files. You can use RMAN with a media manager to back up files to external storage. You can also configure parallelism when backing up or recovering Oracle RAC databases. In Oracle RAC, RMAN channels can be dynamically allocated across all of the Oracle RAC instances. Channel failover enables failed operations on one node to continue on another node. You can start RMAN from Oracle Enterprise Manager Backup Manager or from the command line.

• If you use sequence numbers, then always use CACHE with the NOORDER option for optimal performance in sequence number generation. With the CACHE option, however, you may have gaps in the sequence numbers. If your environment cannot tolerate sequence number gaps, then use the NOCACHE option or consider pre-generating the sequence numbers. If your application requires sequence number ordering but can tolerate gaps, then use CACHE and ORDER to cache and order sequence numbers in Oracle RAC. If your application requires ordered sequence numbers without gaps, then use NOCACHE and ORDER. The NOCACHE and ORDER combination has the most negative effect on performance compared to other caching and ordering combinations.

  Note:

  If your environment cannot tolerate sequence number gaps, then consider pre-generating the sequence numbers or use the ORDER and CACHE options.

  Starting with Oracle Database 18c, you can use scalable sequences to provide better data load scalability instead of configuring a very large sequence cache. Scalable sequences improve the performance of concurrent data load operations, especially when the sequence values are used for populating primary key columns of tables.

• If you use indexes, then consider alternatives, such as reverse key indexes to optimize index performance. Reverse key indexes are especially helpful if you have frequent inserts to one side of an index, such as indexes that are based on insert date.

Many people want to consolidate multiple applications in a single database or consolidate multiple databases in a single cluster. Oracle Clusterware and Oracle RAC support both types of consolidation.

Creating a cluster with a single pool of storage managed by Oracle ASM provides the infrastructure to manage multiple databases whether they are single instance databases or Oracle RAC databases.

Oracle RAC provides concurrent, transactionally consistent access to a single copy of the data from multiple systems. It provides scalability beyond the capacity of a single server. If your application scales transparently on symmetric multiprocessing (SMP) servers, then it is realistic to expect the application to scale well on Oracle RAC, without the need to make changes to the application code.

Traditionally, when a database server runs out of capacity, it is replaced with a new larger server. As servers grow in capacity, they become more expensive. However, for Oracle RAC databases, you have alternatives for increasing the capacity:

• You can migrate applications that traditionally run on large SMP servers to run on clusters of small servers.

• You can maintain the investment in the current hardware and add a new server to the cluster (or create or add a new cluster) to increase the capacity.

Adding servers to a cluster with Oracle Clusterware and Oracle RAC does not require an outage. As soon as the new instance is started, the application can take advantage of the extra capacity.

All servers in the cluster must run the same operating system and same version of Oracle Database but the servers do not have to have the same capacity. With Oracle RAC, you can build a cluster that fits your needs, whether the cluster is made up of servers where each server is a two-CPU commodity server or clusters where the servers have 32 or 64 CPUs in each server. The Oracle parallel execution feature allows a single SQL statement to be divided up into multiple processes, where each process completes a subset of work. In an Oracle RAC environment, you can define the parallel processes to run only on the instance where the user is connected or to run across multiple instances in the cluster.

In addition to using locally managed tablespaces, you can further simplify space administration by using automatic segment space management (ASSM) and automatic undo management.

ASSM distributes instance workloads among each instance's subset of blocks for inserts. This improves Oracle RAC performance because it minimizes block transfers. To deploy automatic undo management in an Oracle RAC environment, each instance must have its own undo tablespace.

As a general rule, only use DDL statements for maintenance tasks and avoid executing DDL statements during peak system operation periods. In most systems, the amount of new object creation and other DDL statements should be limited. Just as in noncluster Oracle databases, excessive object creation and deletion can increase performance overhead.

If you add nodes to your Oracle RAC database environment, then you may need to increase the size of the SYSAUX tablespace. Conversely, if you remove nodes from your cluster database, then you may be able to reduce the size of your SYSAUX tablespace.

If you are running XA Transactions in an Oracle RAC environment and the performance is poor, then direct all branches of a tightly coupled distributed transaction to the same instance by creating multiple Oracle Distributed Transaction Processing (DTP) services, with one or more on each Oracle RAC instance.

Each DTP service is a singleton service that is available on one and only one Oracle RAC instance. All access to the database server for distributed transaction processing must be done by way of the DTP services. Ensure that all of the branches of a single global distributed transaction use the same DTP service. In other words, a network connection descriptor, such as a TNS name, a JDBC URL, and so on, must use a DTP service to support distributed transaction processing.

Cache Fusion makes Oracle RAC databases the optimal deployment servers for online transaction processing (OLTP) applications. This is because these types of applications require:

• High availability if there are failures

• Scalability to accommodate increased system demands

• Load balancing according to demand fluctuations

The high availability features of Oracle Database and Oracle RAC can re-distribute and load balance workloads to surviving instances without interrupting processing. Oracle RAC also provides excellent scalability so that if you add or replace a node, then Oracle Database re-masters resources and re-distributes processing loads.

To accommodate the frequently changing workloads of online transaction processing systems, Oracle RAC remains flexible and dynamic despite changes in system load and system availability. Oracle RAC addresses a wide range of service levels that, for example, fluctuate due to:

• Varying user demands

• Peak scalability issues like trading storms (bursts of high volumes of transactions)

• Varying availability of system resources

This section discusses how to deploy data warehouse systems in Oracle RAC environments by briefly describing the data warehouse features available in shared disk architectures.

This section includes the following topics:

• Speed-Up for Data Warehouse Applications on Oracle RAC

• Parallel Execution in Data Warehouse Systems and Oracle RAC

This section describes the following two Oracle RAC security considerations:

• Transparent Data Encryption and Keystores

• Windows Firewall Considerations

Hang Manager autonomously runs as a DIA0 task within the database.

Figure 13-1 Hang Manager Architecture

Description of "Figure 13-1 Hang Manager Architecture"

Hang Manager works in the following three phases:

• Detect: In this phase, Hang Manager collects the data on all the nodes and detects the sessions that are waiting for the resources held by another session.

• Analyze: In this phase, Hang Manager analyzes the sessions detected in the Detect phase to determine if the sessions are part of a potential hang. If the sessions are suspected as hung, Hang Manager then waits for a certain threshold time period to ensure that the sessions are hung.

• Verify: In this phase, after the threshold time period is up, Hang Manager verifies that the sessions are hung and selects a victim session. The victim session is the session that is causing the hang.

After the victim session is selected, Hang Manager applies hang resolution methods on the victim session. If the chain of sessions or the hang resolves automatically, then Hang Manager does not apply hang resolution methods. However, if the hang does not resolve by itself, then Hang Manager resolves the hang by terminating the victim session. If terminating the session fails, then Hang Manager terminates the process of the session. This entire process is autonomous and does not block resources for a long period and does not affect the performance.

Hang Manager also considers Oracle Database QoS Management policies, performance classes, and ranks that you use to maintain performance objectives.

For example, if a high rank session is included in the chain of hung sessions, then Hang Manager expedites the termination of the victim session. Termination of the victim session prevents the high rank session from waiting too long and helps to maintain performance objective of the high rank session.

You can adjust the sensitivity, and control the size and number of the log files used by Hang Manager.

exec dbms_hang_manager.set(dbms_hang_manager.base_file_size_limit, 104857600);

exec dbms_hang_manager.set(dbms_hang_manager.base_file_set_count,6);

Hang Manager autonomously resolves hangs and continuously logs the resolutions in the database alert logs and the diagnostics in the trace files.

Trace Log File .../oracle/log/diag/rdbms/hm1/hm11/incident/incdir_111/hm11_dia0_11111_i111.trc
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
...
*** 2016-07-16T12:39:02.715475-07:00
HM: Hang Statistics - only statistics with non-zero values are listed

            current number of active sessions 3
              current number of hung sessions 1
  instance health (in terms of hung sessions) 66.67%
       number of cluster-wide active sessions 9
         number of cluster-wide hung sessions 5
   cluster health (in terms of hung sessions) 44.45%

*** 2016-07-16T12:39:02.715681-07:00
Resolvable Hangs in the System
                      Root       Chain Total               Hang
   Hang Hang          Inst Root  #hung #hung  Hang   Hang  Resolution
     ID Type Status   Num  Sess   Sess  Sess  Conf   Span  Action
  ----- ---- -------- ---- ----- ----- ----- ------ ------ -------------------
      1 HANG RSLNPEND    3    44     3     5   HIGH GLOBAL Terminate Process
  Hang Resolution Reason: Although hangs of this root type are typically
    self-resolving, the previously ignored hang was automatically resolved.

kjznshngtbldmp: Hang's QoS Policy and Multiplier Checksum 0x0

  Inst  Sess   Ser             Proc  Wait
   Num    ID    Num      OSPID  Name Event
  ----- ------ ----- --------- ----- -----
      1    111  1234     34567    FG gc buffer busy acquire
      1     22 12345     34568    FG gc current request
      3     44 23456     34569    FG not in wait

2016-07-16T12:39:02.616573-07:00
Errors in file .../oracle/log/diag/rdbms/hm1/hm1/trace/hm1_dia0_i1111.trc  (incident=1111):
ORA-32701: Possible hangs up to hang ID=1 detected
Incident details in: .../oracle/log/diag/rdbms/hm1/hm1/incident/incdir_1111/hm1_dia0_11111_i1111.trc
2016-07-16T12:39:02.674061-07:00
DIA0 requesting termination of session sid:44 with serial # 23456 (ospid:34569) on instance 3
     due to a GLOBAL, HIGH confidence hang with ID=1.
     Hang Resolution Reason: Although hangs of this root type are typically
    self-resolving, the previously ignored hang was automatically resolved.
DIA0: Examine the alert log on instance 3 for session termination status of hang with ID=1.

2016-07-16T12:39:02.707822-07:00
Errors in file .../oracle/log/diag/rdbms/hm1/hm11/trace/hm11_dia0_11111.trc  (incident=169):
ORA-32701: Possible hangs up to hang ID=1 detected
Incident details in: .../oracle/log/diag/rdbms/hm1/hm11/incident/incdir_169/hm11_dia0_30676_i169.trc
2016-07-16T12:39:05.086593-07:00
DIA0 terminating blocker (ospid: 30872 sid: 44 ser#: 23456) of hang with ID = 1
     requested by master DIA0 process on instance 1
     Hang Resolution Reason: Although hangs of this root type are typically
    self-resolving, the previously ignored hang was automatically resolved.
     by terminating session sid:44 with serial # 23456 (ospid:34569)
...
DIA0 successfully terminated session sid:44 with serial # 23456 (ospid:34569) with status 0.