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







MongoDB has grown from a primary JSON key-value retailer to some of the common NoSQL database options in use in the present day. It’s extensively supported and gives versatile JSON doc storage at scale. It additionally gives native querying and analytics capabilities. These attributes have brought about MongoDB to be extensively adopted particularly alongside JavaScript internet purposes.

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

On this put up, we’ll stroll via how CDC works on MongoDB and the way it may be applied, after which delve into the explanation why you may need to implement CDC with MongoDB.

Bifurcation vs Polling vs Change Information Seize

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

  • You may bifurcate knowledge coming in, splitting the information into a number of streams that may be despatched to a number of knowledge sources. Usually, this implies your purposes would submit new knowledge to a queue. This isn’t an ideal possibility as a result of it limits the APIs that your software can use to submit knowledge to be those who resemble a queue. Functions have a tendency to wish the assist of upper degree APIs for issues like ACID transactions. So, this implies we typically need to permit our software to speak on to a database. The applying might submit knowledge by way of a micro-service or software server that talks on to the database, however this solely strikes the issue. These providers would nonetheless want to speak on to the database.
  • You possibly can periodically ballot your entrance finish database and push knowledge into your analytical platform. Whereas this sounds easy, the main points get tough, significantly if you could assist updates to your knowledge. It seems that is onerous to do in apply. And you’ve got now launched one other course of that has to run, be monitored, scale and many others.

So, utilizing CDC avoids these issues. The applying can nonetheless leverage the database options (perhaps by way of a service) and you do not have to arrange a polling infrastructure. However there’s one other key distinction — utilizing CDC provides you with the freshest model of the information. CDC allows true real-time analytics in your software knowledge, assuming the platform you ship the information to can devour 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 gives Kafka supply and sink connectors that can be utilized to put in writing the change occasions to a Kafka matter after which output these adjustments to a different system similar to a database or knowledge lake.


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


It is usually doable to seize MongoDB change knowledge seize occasions utilizing Debezium. In case you are conversant in Debezium, this may be trivial.


MongoDB Change Streams and Rockset

In case your objective 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 efficient selection. The Rockset resolution 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 selection to make use of Kafka, Debezium or a completely built-in resolution like Rockset will rely in your use case, so let’s check out some use circumstances for CDC on MongoDB.

Use Circumstances for CDC on MongoDB

Offloading Analytics

One of many essential use circumstances for CDC on MongoDB is to dump analytical queries. MongoDB has native analytical capabilities permitting you to construct up complicated transformation and aggregation pipelines to be executed on the paperwork. Nevertheless, these analytical pipelines, as a consequence of their wealthy performance, are cumbersome to put in writing as they use a proprietary question language particular to MongoDB. This implies analysts who’re used to utilizing SQL could have a steep studying curve for this new language.

Paperwork in MongoDB can even have complicated buildings. Information is saved as JSON paperwork that may include nested objects and arrays that every one present additional intricacies when build up analytical queries on the information similar to accessing nested properties and exploding arrays to investigate particular person parts.

Lastly, performing giant analytical queries on a manufacturing entrance finish occasion can negatively impression person expertise, particularly if the analytics is being run ceaselessly. This might considerably decelerate learn and write speeds that builders typically need to keep away from, particularly as MongoDB is commonly chosen significantly for its quick write and skim operations. Alternatively, it might require bigger and bigger MongoDB machines and clusters, rising price.

To beat these challenges, it’s common to ship knowledge to an analytical platform by way of CDC in order that queries might be run utilizing acquainted languages similar 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 acceptable analytics platform, whether or not it is a knowledge lake, knowledge warehouse or a real-time analytics database.

Rockset takes this a step additional by not solely straight consuming CDC occasions from MongoDB, but additionally supporting SQL queries natively (together with JOINs) on the paperwork, and gives performance to govern complicated knowledge buildings and arrays, all inside SQL queries. This allows 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 applied options similar to textual content indexes that assist this natively. Textual content indexes permit sure properties to be listed particularly for search purposes. This implies paperwork might be retrieved primarily based on proximity matching and never simply precise matches. You can even embrace a number of properties within the index similar to a product title 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 cases the place offloading to a devoted database for search may be preferable. Once more, efficiency would be the essential purpose particularly if quick writes are necessary. Including textual content indexes to a group in MongoDB will naturally add an overhead on each insertion because of the indexing course of.

In case your use case dictates a richer set of search capabilities, similar to fuzzy matching, then you could need to implement a CDC pipeline to repeat the required textual content knowledge from MongoDB into Elasticsearch. Nevertheless, 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 also be SQL primarily based, 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 a variety 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 resolution 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 cases by offloading load intensive duties, similar to real-time analytics, to a different platform.

MongoDB gives Kafka and Debezium connectors out of the field to help with CDC implementations; nonetheless, relying in your present structure, this may occasionally 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, primarily based on MongoDB change streams, lowering the latency of information ingestion and permitting real-time analytics. With automated indexing and the power to question structured or semi-structured natively with SQL, you may write highly effective queries on knowledge with out the overhead of ETL pipelines, which means queries might be executed on CDC knowledge inside one to 2 seconds of it being produced.

Lewis Gavin has been a knowledge engineer for 5 years and has additionally been running a blog about expertise throughout the Information group 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 navy helicopters. He then went on to work for Capgemini the place he helped the UK authorities transfer into the world of Huge Information. He’s presently utilizing this expertise to assist rework the information panorama at easyfundraising.org.uk, a web based charity cashback web site, the place he’s serving to to form their knowledge warehousing and reporting functionality from the bottom up.


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