In this article, we will explore how to perform a real-time query to access data on a physical standby database in Oracle 19c. Real-time query and standby database are crucial for maintaining high availability and performance. This tutorial provides a comprehensive understanding of these concepts within Oracle 19c.
Understanding Real-Time Query
Real-time selects, or live query, is a key feature of Oracle 19c that allows users to query data on a physical standby database without affecting the primary database. This ensures that the primary database remains available for transactions while read-only operations are performed on the standby database.
Benefits of Real-Time Query: Implementing real-time query in Oracle 19c helps in offloading read operations to the standby database, reducing the load on the primary database. This enhances overall system performance and availability.
Example1: Enabling Real-Time Query:
-- Stop redo apply
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
-- Open standby database in read-only mode
ALTER DATABASE OPEN READ ONLY;
-- Restart redo apply with real-time query enabled
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;
This configuration enables real-time query on the standby database by opening it in read-only mode and then restarting redo apply.
Tools for Managing Real-Time Query: Oracle 19c provides several tools for managing real-time selects, such as Oracle Data Guard and Oracle Enterprise Manager. These tools help administrators monitor and optimize query performance on the standby database.
Preparing for Real-Time Query
Before performing a real-time selects, it is essential to configure the necessary settings and understand the environment.
1. Configuring Init Parameters: Ensure that the initialization parameters related to real-time query are properly configured.
ALTER SYSTEM SET log_archive_dest_state_2=ENABLE SCOPE=BOTH;
ALTER SYSTEM SET db_block_checking=FULL SCOPE=BOTH;
ALTER SYSTEM SET compatible='11.0.0' SCOPE=SPFILE;
2. Monitoring Real-Time Query Usage: Regularly monitor query usage to identify potential performance issues and optimize settings.
Example2: Monitoring Real-Time Query Usage:
SELECT name, value FROM v$sysstat WHERE name LIKE 'physical reads%';
This query provides details about physical reads, indicating the effectiveness of real-time queries.
Accessing Data on a Standby Database
Standby database, or standby access, plays a vital role in Oracle 19c. This process involves querying data on the standby database while the primary database handles transactional operations. Oracle 19c uses advanced replication techniques to ensure data consistency between the primary and standby databases.
Accessing Standby Data: Oracle 19c provides several techniques to access data on the standby database, such as setting up Data Guard and configuring services. These techniques help ensure that the standby database is always in sync with the primary database.
Example3: Configuring Data Guard for Standby Access:
ALTER SYSTEM SET log_archive_dest_2='SERVICE=standby_db';
This code configures Data Guard to replicate data to the standby database, enabling standby access.
Managing Standby Efficiency: Effective standby access involves monitoring synchronization, identifying lag, and ensuring that the standby database is ready for queries. Tools like Oracle Enterprise Manager and V$ views aid in this process.
Example1: Checking Data Guard Status:
SELECT dest_id, status, gap_status FROM v$archive_dest_status;
This query checks the status of Data Guard and identifies any gaps in synchronization.
Implementing Real-Time Query and Standby Access in Oracle 19c
To manage real-time selects and standby access effectively, Oracle 19c utilizes several tools and techniques. These include monitoring query performance, configuring system parameters, and using Oracle Enterprise Manager for real-time insights.
Step-by-Step Implementation:
- Configuring System Parameters: Adjust system parameters to optimize real-time queries and standby access.
ALTER SYSTEM SET log_archive_config='DG_CONFIG=(primary_db,standby_db)' SCOPE=BOTH;
ALTER SYSTEM SET log_archive_dest_2='SERVICE=standby_db' SCOPE=BOTH;
- Monitoring Query Performance: Regularly monitor system statistics to identify issues and optimize performance.
Example2: Monitoring Query Performance:
SELECT instance_name, name, value FROM v$sysstat WHERE name IN ('physical reads', 'db block gets');
- Using Oracle Enterprise Manager: Utilize Oracle Enterprise Manager for comprehensive monitoring and management.
Example3: Viewing Real-Time Queries in OEM: Navigate to the “Performance” tab, then select “Standby Database” to view detailed information about current query performance and potential issues.
- Adjusting Query Settings: Adjust query settings based on monitoring results and advisory recommendations.
Example1: Adjusting Query Settings:
-- Stop redo apply
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
-- Open standby database in read-only mode
ALTER DATABASE OPEN READ ONLY;
-- Restart redo apply with real-time query enabled
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;
Monitoring and Managing Lag in Active DataGuard
Monitoring and managing lag is critical in maintaining real-time query efficiency in Active DataGuard.
Understanding Lag: Lag can occur due to insufficient CPU, high network latency, or limited bandwidth. It is crucial to monitor and manage lag to ensure optimal performance.
Example1: Monitor Apply Lag:
SELECT NAME, VALUE, DATUM_TIME, TIME_COMPUTED FROM V$DATAGUARD_STATS WHERE NAME LIKE 'apply lag';
This query provides details about the apply lag, showing the time difference between the last applied change on the standby and the primary.
Example2: Monitor Apply Lag with Histogram:
SELECT * FROM V$STANDBY_EVENT_HISTOGRAM WHERE NAME = 'apply lag' and count > 0;
This query provides a histogram of the apply lag events on the standby database.
Setting Zero Lag Between Primary and Standby: For applications with zero tolerance for lag, set STANDBY_MAX_DATA_DELAY to zero to ensure real-time synchronization.
Example3: Configure Zero Lag:
ALTER SESSION SET standby_max_data_delay=0;
Benefits of Effective Real-Time Query and Standby Access Management
Effective real-time selects and standby access management, including live query and standby access, offer numerous benefits in an Oracle 19c environment. Firstly, it improves overall system performance by offloading read operations to the standby database. Secondly, it enhances data consistency and integrity by maintaining synchronization between primary and standby databases. Lastly, effective management facilitates easier troubleshooting and resolution of issues.
Performance Improvement: Improving performance is one of the main benefits of effective real-time query and standby access management. By optimizing query settings and reducing load on the primary database, Oracle 19c ensures smooth and efficient database operations.
Enhanced Stability: Enhancing stability is another key benefit. By managing real-time selects and standby access effectively, Oracle 19c reduces the risk of system crashes and data corruption. This results in a more stable and reliable database environment.
Scalability: Scalability is crucial for growing businesses. With effective real-time query and standby access management, Oracle 19c can easily scale to handle increased workloads. By ensuring efficient resource allocation and usage, the system can accommodate more users and higher transaction volumes without compromising performance.
Conclusion
In summary, performing real-time selects to access data on a physical standby database in Oracle 19c is a complex but essential task. By understanding and implementing effective real-time query and standby access management techniques, administrators can ensure optimal performance and stability of their Oracle systems. The key to success lies in continuously monitoring, adjusting, and optimizing query settings to meet the demands of the database system.
See more on Oracle’s website!
Be Oracle Dataguard Certified Professional, this world is full of opportunities for qualified DBAs!
