Simplify ModelarDB: Remove Modelardbm For Easier Deployment

When it comes to deploying distributed databases, complexity is often the enemy of adoption. That's why the team behind ModelarDB is exploring a significant simplification: removing the modelardbm component. This move aims to streamline the deployment process for distributed ModelarDB instances, requiring only a single object store instead of the current necessity of both an object store and a manager. This article delves into the proposed changes, explaining the rationale and the exciting possibilities this simplification unlocks for users and developers alike.

The Current Deployment Challenge and the Promise of Simplification

Currently, getting ModelarDB up and running in a distributed environment involves managing two key components: an object store and a manager. While this setup is functional, it adds an extra layer of configuration and operational overhead. The core idea behind the proposed simplification hinges on the robust capabilities of Delta Lake, the object store technology that ModelarDB utilizes. Delta Lake provides inherent transactional guarantees on a per-table basis. This means that operations on tables are atomic and reliable, offering a strong foundation for managing data integrity. Recognizing this, the developers are investigating whether the manager component (modelardbm) can be effectively merged or its responsibilities migrated to the existing modelardbd instances and the object store itself. The ultimate goal is to make a distributed ModelarDB deployment as straightforward as simply pointing to an object store, significantly lowering the barrier to entry for users looking to leverage distributed data management capabilities.

Leveraging the Object Store as the Single Source of Truth

The cornerstone of the proposed simplification is to establish the object store as the definitive single source of truth for ModelarDB's distributed state. This approach is designed to inherently resolve inconsistencies that might arise between different modelardbd instances. By making the object store the ultimate authority, any discrepancies can be reconciled by referring back to it. For instance, if a modelardbd instance receives a request to write data to a table that it hasn't explicitly been informed about via a create table statement, it can query the object store to verify the table's existence. If the table exists in the object store, the operation can proceed. Conversely, if a modelardbd instance attempts to drop a table, but the table no longer exists in the object store (perhaps due to an earlier, incomplete drop operation or a direct manipulation of the object store), the transfer can be safely rejected. This principle ensures that the state recorded in the object store always dictates the true state of the database, preventing rogue operations and maintaining data integrity across the distributed system. This reliance on the object store for state validation is a critical step in removing the need for a separate managerial component.

Rethinking Workload Balancing and Instance Discovery

With the modelardbm manager out of the picture, new mechanisms are needed for crucial distributed functionalities like workload balancing and instance discovery. The proposed solution involves implementing the get_flight_info() method directly on the modelardbd instances. This method, a standard in data flight protocols, typically returns information about how to connect to and retrieve data. By having modelardbd instances respond to get_flight_info() requests and, importantly, be able to return their own address, they can actively participate in load balancing. When a client or another modelardbd instance queries for information, the responding modelardbd can direct the traffic to itself or, in a more advanced scenario, to other available and less-loaded instances. This distributed approach to routing ensures that requests are handled efficiently across the cluster. Furthermore, for new modelardbd instances to join the cluster and understand the existing topology, they need a way to discover their peers. The plan is for each modelardbd instance to write its address to the object store. This shared location acts as a central registry, allowing any new or existing instance to query the object store and learn about all the other active modelardbd nodes in the cluster. This mechanism replaces the centralized discovery function that modelardbm might have previously provided, fostering a more decentralized and resilient architecture.

Enhancing Inter-Instance Communication with Gossip Protocols

In a distributed system, efficient and reliable communication between nodes is paramount, especially when eliminating a central manager. The proposed architecture for ModelarDB intends to leverage gossip protocols for inter-modelardbd instance communication, particularly in cloud environments. A gossip protocol is a peer-to-peer communication method where nodes periodically exchange information about themselves and other nodes they know about with a random subset of their peers. This decentralized approach ensures that information propagates throughout the cluster organically and efficiently. If one node fails, its information can still reach others through its neighbors. This is significantly more resilient than relying on a single point of communication or coordination. Using a protocol like gossip allows modelardbd instances to stay updated on the status, health, and current workload of their peers. This shared, up-to-date knowledge is crucial for effective workload balancing, fault detection, and overall cluster management, all without a central coordinating entity. The ability for nodes to