Limits

These are the physics, not a temporary bug list.

Envelope

Constraint	Value
DuckDB memory_limit	64 MB
Threads	1
Parquet working-set gate	48 MB
WASM binary	~41 MB (~9.9 MiB gzip)
Paid Worker gzip cap	10 MiB

Cross the working-set gate and the engine should refuse with a graduate-to-native style error. On Cloudflare that native path is not wired yet (HTTP 501).

What fits

• TPC-H SF0.1 (~21 MB, 600k lineitems)
• ClickBench-style 1M hits (~5 MB)
• Warm count / groupby / modest joins in hundreds of ms
• Many idle tenants

What does not

• Multi-GB hot working sets on Workers
• High-cardinality aggs that spill past 64 MB (pnpm memory-boundary)
• Firehose ingest (batch Parquet into R2)
• Hard sub-50ms p99 SLOs

Platform

Workers Paid is required. Free tier dies at 3 MiB gzip. DuckDB alone is basically the whole 10 MiB budget, which is why the engine is its own Worker.

Latency shape

Warm engine wall ~150–300ms on sample groupbys. Client often 400–800ms. Occasional 2–3s outliers with a still-fast wallTimeMs means routing / cold isolate / view reload, not “Parquet is slow.”