docs: RFC — Keboola bez backendu — File-based architektura na S3 + DuckDB (TCRD-17)

[ZdenekSrotyr]

Linear issue: TCRD-17

Changes:

• Adds an RFC document (in Czech) exploring a warehouse-less Keboola architecture using S3 (Parquet) + DuckDB as an alternative to Snowflake/BigQuery backends for cost-sensitive and small-data customers
• Covers: current architecture analysis, proposed "File Backend" storage type, DuckDB transformation flow, metadata catalog options (custom DB vs. DuckLake vs. Iceberg), cost comparisons, performance breakpoints vs. warehouse, PoC pipeline design, risks, and a phased roadmap

Key areas for review:

1. Repo placement — Document lives in a new rfc/ directory. Confirm this is appropriate for developers-docs (which is typically public-facing), or whether it belongs in an internal repo instead.
2. Cost estimates (Section 9) — Based on public Snowflake pricing ($2/credit) and rough S3 cost calculations. Should be validated against actual Keboola customer spend data.
3. DuckDB breakpoint claims (Section 7) — States ~100-200 GB as the crossover point vs. warehouse. These are extrapolated from public benchmarks, not Keboola-specific workloads.
4. DuckLake recommendation (Section 6) — Recommends DuckLake for production metadata catalog. DuckLake is a relatively new project (2025) — warrants discussion on maturity risk.
5. Storage API compatibility assumptions (Section 5) — Claims extractors/writers need no changes due to Common Interface abstraction. Needs validation from someone familiar with Storage API internals.

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This is a research/exploration RFC, not a production code change. No functional impact on existing systems.

Link to Devin session: https://app.devin.ai/sessions/546413c56692420f8ab1ea9e3548a57f
Requested by: @ZdenekSrotyr

[linear]

TCRD-17 Keboola bez backendu — file-based architektura na S3 + DuckDB transformace

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