The Missing MultipartUploads Table: A Database Migration That Unlocks Cross-Node Multipart Coordination

The Message

[assistant] [task] {"description":"Create MultipartUploads table","prompt":"In /home/theuser/gw, create a new CQL migration for the MultipartUploads table needed by the S3 frontend proxy.\n\n1. Look at server/s3frontend/multipart.go to see what columns are needed\n2. Create a new migration file in database/cqldb/migra...
Created the migration file at `database/cqldb/migrations/1756300000_multipart_uploads.up.cql` with the following schema:

- `upload_id` (text) - primary key
- `bucket` (text)
- `key` (text)
- `node_id` (text) - the coordinator node
- `created_at` (timestamp)
- `expires_at` (timestamp)
- `status` (text) - for tracking "active", "completed", "aborted" states

The schema matches the `MultipartUpload` struct and queries in `server/s3frontend/multipart.go:18-26`.

<task_metadata>
session_id: ses_3ee8...

This message, at first glance, appears to be a routine report about creating a database migration file. But beneath its straightforward surface lies a pivotal moment in the construction of a horizontally scalable S3 architecture—a moment where a fundamental architectural assumption was unearthed, examined, and corrected. The creation of the MultipartUploads CQL table was not a simple additive change; it was the direct consequence of recognizing that the architecture had outgrown its original design constraints and needed a new coordination primitive to function correctly across multiple storage nodes.

Context: The Architecture That Needed a Table

To understand why this message was written, we must step back into the broader context of the session. The assistant and user had been building a horizontally scalable S3-compatible storage system on top of the Filecoin Gateway's Kuri storage nodes. The architecture followed a three-layer design: stateless S3 frontend proxies (port 8078) routing requests to independent Kuri storage nodes, which in turn stored data in a shared YugabyteDB database with per-node keyspaces for blockstore data and a shared keyspace for S3 object routing metadata.

This architecture had been through a major correction earlier in the session. The assistant had initially configured Kuri nodes to act as direct S3 endpoints, violating the roadmap's requirement for separate stateless frontend proxy nodes. The user caught this error, and the assistant redesigned the entire test cluster to properly separate the S3 proxy layer from the Kuri storage layer. This architectural reset was the foundation upon which all subsequent work was built.

After the reset, the assistant conducted a comprehensive review of the codebase against the roadmap (message 551-558), identifying several critical gaps. Among the findings were two database schema issues flagged as 🔴 CRITICAL: the S3Objects CQL migration was missing the node_id and expires_at columns, and the MultipartUploads table did not exist at all. The user then reported (message 559) that the UIs on ports 9010 and 8078 were failing to load, and explicitly instructed: "fix S3 schema and update related code, add multiparts table."

Why This Table Was Never Needed Before

The user's explanation for why the MultipartUploads table was now necessary is one of the most illuminating parts of the conversation. They wrote: "it wasn't needed before because we used unixfs dags which had all related blocks in one blockstore but now it's no longer the case / we have multiple blockstores."

This single sentence reveals the entire architectural shift that made the new table essential. In the previous design, when multipart uploads were assembled, all the blocks of the resulting file were stored in a single blockstore—specifically, the blockstore of the Kuri node that coordinated the upload. The UnixFS DAG (Directed Acyclic Graph) format used by IPFS/Filecoin naturally groups all related blocks into one data structure. If all blocks live in one place, you don't need a global registry of multipart uploads; you can track them locally within that node's blockstore.

But the scalable architecture changed this fundamentally. With multiple Kuri storage nodes, each having its own isolated blockstore (via per-node RIBS keyspaces), a multipart upload's parts could be distributed across different nodes. The S3 frontend proxy, which is stateless and can run on any node, needs to know which parts belong to which upload, where they are stored, and what state the upload is in. This information must be globally visible across all nodes, which means it must live in the shared database layer—not in any single node's private blockstore.

The MultipartUploads table was the solution to this coordination problem. It provides a single source of truth for multipart upload state that any S3 proxy or Kuri node can query, regardless of which node originally initiated or coordinated the upload.

Input Knowledge Required

To fully understand this message, several pieces of prior knowledge are essential:

The CQL Migration System: The migration file lives in database/cqldb/migrations/ and follows a naming convention of Unix timestamps with .up.cql suffixes. The assistant had already fixed the S3Objects migration in the preceding message (index 565), adding node_id and expires_at columns. The new migration for MultipartUploads would follow the same pattern.

The Multipart Upload Code: The assistant referenced server/s3frontend/multipart.go:18-26 as the source of truth for the schema. This file contains the Go struct definition and CQL queries for multipart upload tracking. The assistant had reviewed this file during the earlier codebase audit (message 557) and understood its requirements.

The Three-Layer Architecture: The distinction between the stateless S3 frontend proxy (port 8078), the Kuri storage nodes (each with independent RIBS keyspaces), and the shared YugabyteDB (with both per-node and shared keyspaces) is the conceptual framework that makes this table meaningful. Without understanding that the S3 proxy needs to coordinate across multiple Kuri nodes, the need for a globally visible multipart uploads table would not be apparent.

The UnixFS DAG Context: The user's explanation about why the table wasn't needed before—because UnixFS DAGs kept all related blocks in one blockstore—is crucial background. This is a domain-specific insight about how IPFS/Filecoin data structures work, and it directly motivated the architectural change.

Output Knowledge Created

This message produced several concrete outputs:

  1. A new migration file at database/cqldb/migrations/1756300000_multipart_uploads.up.cql containing the CQL CREATE TABLE statement for the MultipartUploads table.
  2. A defined schema with seven columns: upload_id (text, primary key), bucket (text), key (text), node_id (text) for the coordinator node, created_at (timestamp), expires_at (timestamp), and status (text) for tracking "active", "completed", "aborted" states.
  3. Schema-to-code alignment: The assistant explicitly verified that the schema matches the MultipartUpload struct and queries in server/s3frontend/multipart.go:18-26, ensuring that the database layer and the application layer are consistent.
  4. A coordination primitive: The table enables the S3 frontend proxy to query the status and location of any multipart upload across the entire cluster, regardless of which Kuri node is handling the request. This is essential for the "complete multipart upload" operation, which needs to assemble parts that may be stored on different nodes.

The Decision Process

The decision to create this table was not made in isolation. It emerged from a chain of reasoning that spanned multiple messages:

  1. Review identified the gap: In message 558, the assistant's codebase review flagged the missing MultipartUploads table as a 🔴 CRITICAL issue, noting "No migration exists."
  2. User confirmed the priority: In message 559, the user explicitly listed "add multiparts table" as a required fix, providing the UnixFS DAG reasoning that explained why the table was now needed.
  3. Commits were staged first: The user instructed "But first - make commits for all changes so far," and the assistant executed 14 logical commits across messages 560-564, covering configuration, interfaces, Kuri S3 plugin changes, dual CQL connections, the s3frontend package, build system, test cluster infrastructure, documentation, and database schema fixes.
  4. S3Objects migration was fixed first: Message 565 (immediately preceding the subject message) fixed the S3Objects migration to include node_id and expires_at. This was the companion schema fix.
  5. The MultipartUploads migration was created: The subject message (566) completes the database schema work by adding the missing table. The assistant used a sub-agent task pattern throughout, delegating the migration creation to an automated agent with a specific prompt. This approach, suggested by the user in message 559 ("Use agents for everything even if not really needed - this will save top level context"), allowed the assistant to parallelize work while keeping the conversation focused on high-level decisions.

Assumptions and Potential Issues

Several assumptions underlie this message:

The migration will be applied to new deployments only: The roadmap explicitly states "No migration files - new deployments only" for the scalable architecture. The assistant is creating migration files that would be run against a fresh YugabyteDB instance, not patching an existing production database. This is consistent with the overall approach.

The schema matches the application code: The assistant asserts that the schema matches server/s3frontend/multipart.go:18-26. This is a critical correctness claim—if the Go struct and the CQL table are out of sync, queries will fail at runtime. The assistant verified this by reading the multipart.go file during the earlier review.

The node_id column identifies the coordinator, not necessarily the storage location: The schema includes node_id as "the coordinator node." This is subtly different from the node_id in the S3Objects table, which identifies the node storing the object. For multipart uploads, the coordinator node is the one that initiated the upload, but individual parts may be stored on different nodes. The complete multipart upload operation will need to query both tables to assemble the final object.

The status field is sufficient for state tracking: The schema uses a simple text field with values "active", "completed", "aborted". This is a straightforward state machine, but it assumes that no additional states (like "failed" or "expired") will be needed, and that concurrent operations won't create race conditions on status transitions.

The Thinking Process Visible in the Message

The message itself is a task report, so it doesn't contain extensive reasoning traces. However, the structure of the report reveals the assistant's thinking:

  1. The task description shows the method: The prompt instructs the agent to "Look at server/s3frontend/multipart.go to see what columns are needed." This indicates a deliberate, code-driven approach: derive the database schema from the application code, not from abstract design documents.
  2. The response confirms alignment: By stating "The schema matches the MultipartUpload struct and queries," the assistant is performing a cross-reference validation. This is not just a creation report—it's a correctness assertion.
  3. The column list is prioritized: The columns are listed in a specific order, with upload_id first as the primary key. The node_id column is annotated with "the coordinator node," showing the assistant's understanding of its role in the distributed architecture.
  4. The migration timestamp is chosen: The file is named 1756300000_multipart_uploads.up.cql. The timestamp 1756300000 is a Unix timestamp (approximately June 2025), chosen to be after the existing 1754293669_init_s3_object_index.up.cql migration. This ordering ensures that the S3Objects table is created before the MultipartUploads table, which is a logical dependency since multipart uploads reference objects.

Conclusion

The creation of the MultipartUploads migration file was a small but essential piece of a much larger architectural puzzle. It represents the moment when the system's distributed nature was fully acknowledged in the database schema—when the design stopped pretending that all data lives in one place and started providing the coordination infrastructure that a multi-node system requires. The table is, in essence, a distributed state machine for multipart uploads, enabling the stateless S3 frontend proxies to orchestrate complex multi-node operations without any single node holding all the state.

This message also illustrates a broader principle of distributed systems design: the database schema is not just a data storage concern—it is an architectural document. Every table, every column, every key choice encodes assumptions about how the system will behave under load, how it will scale, and how its components will coordinate. The MultipartUploads table, with its node_id coordinator field and its status state machine, tells the story of a system that learned it could no longer keep all its state in one place and had to build bridges between its distributed parts.