Oracle Change Data Capture – An Event-Driven Architecture for Cloud Adoption
How to replace batch ETL by event-driven distributed stream processing
Use non-intrusive CDC to Kafka to create persistent streams that can be accessed by multiple consumers and automatically reflect upstream schema changes
Tools you need
Striim’s unified data integration and streaming platform connects clouds, data and applications.
Oracle is a multi-model relational database management system.
Kafka is an open-source event-streaming platform
Azure Cosmos is a fully managed NoSQL database.
Azure Blob Storage
Azure Blob Storage is an object store designed to store massive amounts of unstructured data.
All businesses rely on data. Historically, this data resided in monolithic databases, and batch ETL processes were used to move that data to warehouses and other data stores for reporting and analytics purposes. As businesses modernize, looking to the cloud for analytics, and
striving for real-time data insights, they often find that these databases are difficult to completely replace, yet the data and transactions happening within them are essential for analytics. With over 80% of businesses noting that the volume &
velocity of their data is rapidly increasing, scalable cloud adoption and change data capture from databases like Oracle, SQLServer, MySQL and others is more critical than ever before. Oracle change data capture is specifically one area where companies are seeing an influx of modern data
integration use cases.
To resolve this, more and more companies are moving to event-driven architectures, because of the dynamic distributed scalability which makes sharing large volumes of data across systems possible.
In this post we will look at an example which replaces batch ETL by event-driven distributed stream processing: Oracle change data capture events are extracted as they are created; enriched with in-memory,
SQL-based denormalization; then delivered to the Azure Cloud to provide scalable, real-time, low-cost analytics, without affecting the source database. We will also look at using the enriched events, optionally backed by Kafka, to incrementally add other event-driven applications or services.
Event-Driven Architecture Patterns
Most business data is produced as a sequence of events, or an event stream: for example, web or mobile app interactions, devices, sensors, bank transactions, all continuously generate events. Even the current state of a database is the outcome of a sequence of events.
Treating state as the result of a sequence of events forms the core of several event-driven patterns.
Event Sourcing is an architectural pattern in which the state of the application is determined by a sequence of events. As an example, imagine that each “event” is an incremental update to an entry in a database. In this case, the
state of a particular entry is simply the accumulation of events pertaining to that entry. In the example below the stream contains the queue of all deposit and withdrawal events, and the database table persists the current account balances.
The events in the stream can be used to reconstruct the current account balances in the database, but not the other way around. Databases can be replicated with a technology called Change Data Capture (CDC), which collects the changes being applied to a source database, as soon as they occur by
monitoring its change log, turns them into a stream of events, then applies those changes to a target database. Source code version control is another well known example of this, where the current state of a file is some base version, plus the accumulation of all changes that have been made to
What if you need to have the same set of data for different databases, for different types of use? With a stream, the same message can be processed by different consumers for different purposes. As shown below, the stream can act as a distribution point, where, following the polygot persistence pattern, events can be delivered to a variety of data stores, each using the most suited technology for a particular use case or materialized view.
Event-Driven Streaming ETL Use Case Example
Below is a diagram of the Event-Driven Streaming ETL use case example:
Striim’s low-impact, real-time Oracle change data capture (CDC) feature is used to stream database changes (inserts, updates and deletes) from an Operational Oracle database into Striim
CDC Events are enriched and denormalized with Streaming SQL and Cached data, in order to make relevant data available together
Enriched, denormalized events are streamed to CosmosDB for real-time analytics
Enriched streaming events can be monitored in real time with the Striim Web UI, and are available for further Streaming SQL analysis, wizard-based dashboards, and other applications on-premise
or in the cloud.
Replacing Batch Extract with Real Time Streaming of CDC Order Events
Striim’s easy-to-use CDC wizards automate the creation of applications that leverage change data capture, to stream events as they are created, from various source systems to various targets. In this example, shown below, we use Striim’s OracleReader (Oracle Change Data Capture) to read the Order OLTP transactions in Oracle redo logs and stream these insert, update, delete operations, as soon as the transactions commit, into Striim, without impacting the performance of the source database.
Utilizing Caches For Enrichment
Relational Databases typically have a normalized schema which makes storage efficient, but causes joins for queries, and does not scale well horizontally. NoSQL databases typically have a denormalized schema which scales across a cluster because data that is read together is stored together.
With a normalized schema, a lot of the data fields will be in the form of IDs. This is very efficient for the database, but not very useful for downstream queries or analytics without any meaning or context. In this example we want to enrich the raw Orders data with reference data from the SalesRep table, correlated by the Order Sales_Rep_ID, to produce a denormalized record including the Sales Rep Name and Email information in order to make analysis easier by making this data available together.
Since the Striim platform is a high-speed, low latency, SQL-based stream processing platform, reference data also needs to be loaded into memory so that it can be joined with the streaming data without slowing things down. This is achieved through the use of the Cache component. Within the Striim platform, caches are backed by a distributed in-memory data grid that can contain millions of reference items distributed around a Striim cluster. Caches can be loaded from database queries, Hadoop, or files, and maintain data in-memory so that joining with them can be very fast. In this example, shown below, the cache is loaded with a query on the SalesRep table using the Striim DatabaseReader.
Joining Streaming and Cache Data For Real Time Transforming and Enrichment With SQL
We can process and enrich data-in-motion using continuous queries written in Striim’s SQL-based stream processing language. Using a SQL-based language is intuitive for data processing tasks, and most common SQL constructs can be utilized in a streaming environment. The main differences between using SQL for stream processing, and its more traditional use as a database query language, are that all processing is in-memory, and data is processed continuously, such that every event on an input data stream to a query can result in an output.
This is the query we will use to process and enrich the incoming data stream:
In this query we select the Order stream and SalesRep cache fields that we want, apply transformations to convert data types, put the Order stream and SalesRep cache in the FROM clause, and include a join on SALES_REP_ID as part of the WHERE clause. The result of this query is to continuously output enriched (denormalized) events, shown below, for every CDC event that occurs for the Orders table. So with this approach we can join streams from an Oracle Change Data Capture reader with cached data for enrichment.
Loading the Enriched Data to the Cloud for Real Time Analytics
Now the Oracle CDC (Oracle change data capture) data, streamed and enriched through Striim,
can be stored simultaneously in Azure Cloud blob storage and Azure Cosmos DB, for elastic storage with advanced big data analytics, using the Striim AzureBlobWriter
and the CosmosDBWriter shown below.
The image below shows the Striim flow web UI for our streaming ETL application. Flows define what data an application receives, how it processes the data, and what it does with the results.
Using Kafka for Streaming Replay and Application Decoupling
The enriched stream of order events can be backed by or published to Kafka for stream persistence, laying the foundation for streaming replay and application decoupling. Striim’s native Integration with Apache Kafka makes it quick and easy to leverage Kafka to make every data source re-playable, enabling recovery even for streaming sources that cannot be rewound. This also acts to decouple applications, enabling multiple applications to be powered by the same data source, and for new applications, caches or views
to be added later.
Streaming SQL for Aggregates
We can further use Striims Streaming SQL on the denormalized data to make a real time stream of summary metrics about the events being processed available to Striim
Real-Time Dashboards and other applications. For example, to create a running count and sum of orders per SalesRep in the last hour, from the stream of enriched orders, you would use a window, and the familiar group by clause.
CREATE WINDOW OrderWindow
KEEP WITHIN 1 HOUR
PARTITION BY sales_rep_id
SELECT sales_rep_id, sales_rep_Name,
COUNT(*) as orderCount,
SUM(order_total) as totalAmount
GROUP BY sales_rep_id
With the Striim Monitoring Web UI we can now monitor our data pipeline with real-time information for the cluster, application components, servers, and agents. The Main monitor page allows to visualize summary statistics for Events
Processed, App CPU%, Server Memory, or Server CPU%. Below the Monitor App page displays our App Resources, Performance and Components.
Clicking on an app component ‘more details’ button will display more detailed performance information such as CPU and Event rate as shown below:
In this blog post, we discussed how we can use Striim to:
Use streaming SQL and caches to easily denormalize data in order to make relevant data available together
Load streaming enriched data to the cloud for real-time analytics
Use Kafka for persistent streams
Create rolling aggregates with streaming SQL
Continuously monitor data pipelines
To read more about real-time data ingestion, please visit our Real-Time Data Integration solutions page.
To learn more about the power of streaming SQL, visit Striim Platform Overview product page, schedule a demo with a Striim technologist, or download a free trial of the platform and try it for yourself!
To learn more about Striim’s capabilities to support the data integration requirements for an Azure hybrid cloud architecture check out all of Striim’s solutions for Azure.