Lambda Reader Pattern¶

RockLake supports a read-only serverless reader pattern for AWS Lambda and similar Function-as-a-Service environments. A Lambda function can query the catalog without running a persistent sidecar or holding a write lock.

Architecture¶

     ┌─────────────────────────────────────┐
     │  AWS Lambda (cold start: ~200ms)    │
     │                                     │
     │  1. open DbReader (no Db writer)    │
     │  2. read checkpoint-pinned snapshot │
     │  3. list_data_files(table_id)       │
     │  4. return JSON response            │
     └──────────────┬──────────────────────┘
                    │  S3 GetObject (SST files)
                    ▼
     ┌─────────────────────────────────────┐
     │  Amazon S3 Express One Zone         │
     │  (catalog prefix, read-only)        │
     └─────────────────────────────────────┘

Key Properties¶

• No writer handle opened. The handler uses CatalogClientBuilder which opens the store in read-only mode. No write epochs are acquired.
• Checkpoint-pinned reads. By pinning a named checkpoint with rocklake checkpoint pin --name release --snapshot-id N, the Lambda always reads a stable, well-known snapshot even if concurrent writers advance the catalog.
• /tmp caching. On warm invocations the SlateDB SST files cached in /tmp avoid re-downloading from S3 Express, reducing cold-start latency to under 50ms on subsequent calls.

IAM Policy¶

Minimum required permissions for the Lambda execution role:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:ListBucket",
        "s3express:CreateSession"
      ],
      "Resource": [
        "arn:aws:s3:::my-rocklake-bucket/catalog/*",
        "arn:aws:s3:::my-rocklake-bucket"
      ]
    }
  ]
}

Pinning a Checkpoint for Lambda Readers¶

Before deploying a Lambda release, pin a named checkpoint so readers always get a stable view:

# Pin the current latest snapshot as "production"
rocklake checkpoint pin --name production --snapshot-id $(rocklake snapshot current)

# List all pins
rocklake checkpoint list

# Unpin when no longer needed
rocklake checkpoint unpin --name production

Example Handler¶

See crates/rocklake-client/examples/lambda_reader.rs for a complete example handler that:

1. Opens the catalog from ROCKLAKE_CATALOG_URI
2. Lists data files for ROCKLAKE_TABLE_ID
3. Prints them as a JSON-compatible list

To build and test locally:

ROCKLAKE_CATALOG_URI=file:///tmp/my-catalog \
ROCKLAKE_TABLE_ID=1 \
cargo run --example lambda_reader -p rocklake-client

Cold-Start Latency¶

S3 Express One Zone is recommended for the catalog prefix to minimise cold-start latency. See S3 Express Validation for acceptance benchmarks.