Lesson 1

The purpose of this module is to examine the new Oracle features related to distributed databases. As you know, Oracle software is evolving constantly to improve database connectivity between distributed systems. With the introduction of Oracle, we see several new features that improve connectivity between remote databases and offer improved security and replication reliability.
After completing this module, you will be able to:

1. List primary Oracle enhancements for distributed databases
2. Work with queue propagation
3. Describe enhanced LOB support in Oracle
4. Monitor replication by querying V$ views
5. Implement snapshot security
6. Walk through the steps for creating snapshots offline
7. Identify the new features of snapshot deployment templates

The objective of this module is to provide you with enough detailed information about the new Oracle distributed features to enable you to use them in your organization and to understand their functions well enough to pass the OCT exam. This module assumes that you already have a baseline understanding of Oracle distributed database concepts, including snapshots and replication techniques. Let us began by taking a closer look at each of the enhancements for distributed databases.

Oracle has introduced several enhancements for distributed databases between Oracle 12c (released in 2013) and Oracle 19c (released in 2019). These improvements focus on performance, scalability, availability, and ease of management in distributed environments. Below is a list of the primary enhancements relevant to distributed databases:

1. Multitenant Architecture Enhancements
   • Oracle 12c: Introduced the multitenant architecture with Container Databases (CDBs) and Pluggable Databases (PDBs), allowing multiple databases to share a single instance. Distributed database operations could leverage this for consolidation and simplified management across nodes.
   • Oracle 19c: Enhanced multitenant capabilities with features like:
     • PDB Snapshot Carousel: Improved point-in-time recovery and cloning for distributed PDBs, making it easier to manage distributed data snapshots.
     • Hot Cloning: Enabled cloning of PDBs without downtime, improving availability in distributed setups.
     • Increased PDB Scalability: Support for up to 252 PDBs per CDB in 12c grew to more efficient resource management and higher consolidation density by 19c.
2. Data Guard Improvements
   • Oracle 12c: Introduced Active Data Guard with real-time query offloading to standby databases and Far Sync for zero-data-loss replication over long distances.
   • Oracle 19c: Enhanced Data Guard with:
     • Automatic Flashback Standby: When a primary database flashes back, the standby automatically follows, improving consistency in distributed disaster recovery.
     • Multi-Instance Redo Apply: Parallel redo application across multiple RAC instances on the standby, boosting performance in distributed high-availability setups.
     • DML Redirection: Allowed DML operations on Active Data Guard standbys to be redirected to the primary, enhancing read-write separation in distributed systems.
3. Global Data Services (GDS)
   • Oracle 12c: Introduced GDS to manage load balancing and failover across distributed databases, particularly in Oracle RAC and Data Guard environments.
   • Oracle 19c: Improved GDS with:
     • Better Service Management: Enhanced connection pooling and workload routing across geographically distributed databases.
     • Simplified Configuration: Easier integration with sharded databases and replicas, improving distributed application performance.
4. Sharding Enhancements
   • Oracle 12c: Introduced database sharding as a scalability feature, allowing horizontal partitioning of data across independent databases (shards) with a shard catalog for coordination.
   • Oracle 19c: Advanced sharding with:
     • Automated Shard Management: Improved tools for rebalancing and splitting shards without downtime.
     • Direct Routing: Applications can connect directly to shards without always going through the shard catalog, reducing latency in distributed queries.
     • Support for JSON and Spatial Data: Enhanced sharding compatibility with modern data types, making it more versatile for distributed applications.
5. In-Memory Enhancements
   • Oracle 12c: Introduced the In-Memory Column Store for accelerating queries, available in distributed setups like RAC.
   • Oracle 19c: Extended In-Memory features with:
     • Automatic In-Memory Management: Optimized memory usage across distributed nodes without manual intervention.
     • In-Memory Active Data Guard: Allowed standby databases to use In-Memory Column Store for real-time analytics, enhancing distributed query performance.
6. Real Application Clusters (RAC) Improvements
   • Oracle 12c: Enhanced RAC with Flex Clusters and improved scalability for distributed workloads.
   • Oracle 19c: Added:
     • Autonomous Health Framework: Proactive monitoring and self-healing for RAC nodes in distributed environments.
     • Zero-Downtime Patching: Reduced disruptions during maintenance across distributed RAC clusters.
7. Advanced Replication
   • Oracle 12c: Continued support for Oracle GoldenGate and basic replication features for distributed data synchronization.
   • Oracle 19c: Improved replication with:
     • GoldenGate Integration: Tighter integration with Oracle Database for real-time data replication across distributed systems.
     • Conflict Resolution Enhancements: Better handling of data conflicts in multi-master replication setups.
8. Performance and Query Optimization
   • Oracle 12c: Introduced Adaptive Query Optimization and improved distributed query execution plans.
   • Oracle 19c: Enhanced with:
     • Quarantine of Rogue SQL: Prevented poorly performing distributed queries from impacting system-wide performance.
     • Real-Time Statistics: Improved execution plans for distributed queries by gathering statistics dynamically.
9. Security Enhancements
   • Oracle 12c: Added Transparent Data Encryption (TDE) and Data Redaction for distributed environments.
   • Oracle 19c: Strengthened security with:
     • Online Encryption: Enabled tablespace encryption without downtime, critical for distributed databases.
     • Privilege Analysis: Improved auditing and control of access across distributed nodes.
10. Backup and Recovery
    • Oracle 12c: Enhanced Recovery Manager (RMAN) for distributed backup operations.
    • Oracle 19c: Added:
      • Cross-Platform PDB Backups: Simplified backup and restore across distributed multitenant environments.
      • Standby Duplication Improvements: Faster creation of standby databases for distributed recovery.

These enhancements collectively improve Oracle’s capabilities for distributed databases by focusing on scalability (sharding, multitenant), availability (Data Guard, RAC), performance (In-Memory, query optimization), and management simplicity (GDS, automation). Let me know if you’d like a deeper dive into any specific feature!

When an organization is geographically dispersed, it may choose to store its databases on a central database server or to distribute them to local servers (or a combination of both). A distributed database is a single logical database that is spread physically across computers in multiple locations that are connected by a data communications network. We emphasize that a distributed database is truly a database, not a loose collection of files. The distributed database is still centrally administered as a corporate resource while providing local flexibility and customization. The network must allow the users to share the data; thus a user (or program) at location A must be able to access (and perhaps update) data at location B. The sites of a distributed system may be spread over a large area (e.g., the United States or the world) or over a small area (e.g., a building or campus). The computers may range from PCs to large-scale servers or even supercomputers. A distributed database requires multiple instances of a database management system (or several DBMSs), running at each remote site. The degree to which these different DBMS instances cooperate, or work in partnership, and whether there is a master site that coordinates requests involving data from multiple sites distinguish different types of distributed database environments.

• Distributed Database System
  A distributed database system allows applications to access data from local and remote databases. In a homogenous distributed database system, each database is an Oracle Database. In a heterogeneous distributed database system, at least one of the databases is not an Oracle Database. Distributed databases use a client/server architecture to process information requests. This section contains the following topics:
  
  1. Homogenous Distributed Database Systems
  2. Heterogeneous Distributed Database Systems
  3. Client/Server Database Architecture