MongoDB CDC: When to Use Kafka, Debezium, Change Streams, Rockset


MongoDB has grown from a fundamental JSON key-value retailer to one of the fashionable NoSQL database options in use at the moment. It’s broadly supported and supplies versatile JSON doc storage at scale. It additionally supplies native querying and analytics capabilities. These attributes have precipitated MongoDB to be broadly adopted particularly alongside JavaScript internet purposes.

As succesful as it’s, there are nonetheless situations the place MongoDB alone cannot fulfill all the necessities for an utility, so getting a duplicate of the information into one other platform by way of a change information seize (CDC) answer is required. This can be utilized to create information lakes, populate information warehouses or for particular use instances like offloading analytics and textual content search.

On this submit, we’ll stroll by way of how CDC works on MongoDB and the way it may be carried out, after which delve into the the explanation why you may need to implement CDC with MongoDB.

Bifurcation vs Polling vs Change Information Seize

Change information seize is a mechanism that can be utilized to maneuver information from one information repository to a different. There are different choices:

  • You may bifurcate information coming in, splitting the information into a number of streams that may be despatched to a number of information sources. Typically, this implies your purposes would submit new information to a queue. This isn’t an ideal possibility as a result of it limits the APIs that your utility can use to submit information to be those who resemble a queue. Functions have a tendency to wish the help of upper stage APIs for issues like ACID transactions. So, this implies we usually need to permit our utility to speak on to a database. The appliance may submit information by way of a micro-service or utility server that talks on to the database, however this solely strikes the issue. These companies would nonetheless want to speak on to the database.
  • You could possibly periodically ballot your entrance finish database and push information into your analytical platform. Whereas this sounds easy, the small print get tough, notably if you have to help updates to your information. It seems that is arduous to do in observe. And you’ve got now launched one other course of that has to run, be monitored, scale and so forth.

So, utilizing CDC avoids these issues. The appliance can nonetheless leverage the database options (possibly by way of a service) and you do not have to arrange a polling infrastructure. However there may be one other key distinction — utilizing CDC provides you with the freshest model of the information. CDC permits true real-time analytics in your utility information, assuming the platform you ship the information to can eat the occasions in actual time.

Choices For Change Information Seize on MongoDB

Apache Kafka

The native CDC structure for capturing change occasions in MongoDB makes use of Apache Kafka. MongoDB supplies Kafka supply and sink connectors that can be utilized to jot down the change occasions to a Kafka subject after which output these adjustments to a different system akin to a database or information lake.


The out-of-the-box connectors make it pretty easy to arrange the CDC answer, nonetheless they do require using a Kafka cluster. If this isn’t already a part of your structure then it could add one other layer of complexity and price.


It is usually potential to seize MongoDB change information seize occasions utilizing Debezium. If you’re conversant in Debezium, this may be trivial.


MongoDB Change Streams and Rockset

In case your aim is to execute real-time analytics or textual content search, then Rockset’s out-of-the-box connector that leverages MongoDB change streams is an effective alternative. The Rockset answer requires neither Kafka nor Debezium. Rockset captures change occasions straight from MongoDB, writes them to its analytics database, and robotically indexes the information for quick analytics and search.


Your alternative to make use of Kafka, Debezium or a totally built-in answer like Rockset will rely in your use case, so let’s check out some use instances for CDC on MongoDB.

Use Circumstances for CDC on MongoDB

Offloading Analytics

One of many principal use instances for CDC on MongoDB is to dump analytical queries. MongoDB has native analytical capabilities permitting you to construct up advanced transformation and aggregation pipelines to be executed on the paperwork. Nonetheless, these analytical pipelines, resulting from their wealthy performance, are cumbersome to jot down as they use a proprietary question language particular to MongoDB. This implies analysts who’re used to utilizing SQL can have a steep studying curve for this new language.

Paperwork in MongoDB may also have advanced buildings. Information is saved as JSON paperwork that may comprise nested objects and arrays that every one present additional intricacies when increase analytical queries on the information akin to accessing nested properties and exploding arrays to investigate particular person parts.

Lastly, performing massive analytical queries on a manufacturing entrance finish occasion can negatively impression consumer expertise, particularly if the analytics is being run steadily. This might considerably decelerate learn and write speeds that builders typically need to keep away from, particularly as MongoDB is usually chosen notably for its quick write and skim operations. Alternatively, it will require bigger and bigger MongoDB machines and clusters, growing value.

To beat these challenges, it’s common to ship information to an analytical platform by way of CDC in order that queries may be run utilizing acquainted languages akin to SQL with out affecting efficiency of the front-end system. Kafka or Debezium can be utilized to extract the adjustments after which write them to an appropriate analytics platform, whether or not it is a information lake, information warehouse or a real-time analytics database.

Rockset takes this a step additional by not solely straight consuming CDC occasions from MongoDB, but in addition supporting SQL queries natively (together with JOINs) on the paperwork, and supplies performance to control advanced information buildings and arrays, all inside SQL queries. This permits real-time analytics as a result of the necessity to rework and manipulate the paperwork earlier than queries is eradicated.

Search Choices on MongoDB

One other compelling use case for CDC on MongoDB is to facilitate textual content searches. Once more, MongoDB has carried out options akin to textual content indexes that help this natively. Textual content indexes permit sure properties to be listed particularly for search purposes. This implies paperwork may be retrieved based mostly on proximity matching and never simply actual matches. You can even embrace a number of properties within the index akin to a product identify and an outline, so each are used to find out whether or not a doc matches a selected search time period.

Whereas that is highly effective, there should be some situations the place offloading to a devoted database for search is likely to be preferable. Once more, efficiency would be the principal purpose particularly if quick writes are essential. Including textual content indexes to a set in MongoDB will naturally add an overhead on each insertion as a result of indexing course of.

In case your use case dictates a richer set of search capabilities, akin to fuzzy matching, then it’s possible you’ll need to implement a CDC pipeline to repeat the required textual content information from MongoDB into Elasticsearch. Nonetheless, Rockset continues to be an possibility in case you are pleased with proximity matching, need to offload search queries, and likewise retain all the real-time analytics advantages mentioned beforehand. Rockset’s search functionality can be SQL based mostly, which once more may cut back the burden of manufacturing search queries as each Elasticsearch and MongoDB use bespoke languages.


MongoDB is a scalable and highly effective NoSQL database that gives plenty of performance out of the field together with quick learn (get by major key) and write speeds, JSON doc manipulation, aggregation pipelines and textual content search. Even with all this, a CDC answer should allow better capabilities and/or cut back prices, relying in your particular use case. Most notably, you may need to implement CDC on MongoDB to cut back the burden on manufacturing situations by offloading load intensive duties, akin to real-time analytics, to a different platform.

MongoDB supplies Kafka and Debezium connectors out of the field to help with CDC implementations; nonetheless, relying in your present structure, this will likely imply implementing new infrastructure on prime of sustaining a separate database for storing the information.

Rockset skips the requirement for Kafka and Debezium with its inbuilt connector, based mostly on MongoDB change streams, decreasing the latency of information ingestion and permitting real-time analytics. With automated indexing and the flexibility to question structured or semi-structured natively with SQL, you possibly can write highly effective queries on information with out the overhead of ETL pipelines, that means queries may be executed on CDC information inside one to 2 seconds of it being produced.

Lewis Gavin has been an information engineer for 5 years and has additionally been running a blog about abilities inside the Information neighborhood for 4 years on a private weblog and Medium. Throughout his laptop science diploma, he labored for the Airbus Helicopter workforce in Munich enhancing simulator software program for army helicopters. He then went on to work for Capgemini the place he helped the UK authorities transfer into the world of Massive Information. He’s at present utilizing this expertise to assist rework the information panorama at, a web-based charity cashback website, the place he’s serving to to form their information warehousing and reporting functionality from the bottom up.


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