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Known limitations

Stated as limitations, with where each stands. The specs linked are in the repository.

  • Experimental, first release in preparation. v0.1.0 on the DuckDB v1.5.5 line; until it is published the extension is built from source.
  • Mutually exclusive with the stock ducklake extension, and it must be loaded before the first ATTACH 'ducklake:…' (why).
  • Slower than the PostgreSQL backend overall: 1.54x on the whole 1000-table benchmark, with commits at or near parity since the batch goes to the server as T-SQL (specs/014); what remains is the first inlined write into a table (2.9x), commits of many files (5x — their rows go through DuckDB's appender until the mssql extension's bulk-load insert on the DuckDB 2.0 line), the flush (1.6x) and the attach (Performance).
  • Every first touch of a table pays a plan compile in the mssql extension's per-table metadata query when the catalog's database is not forced-parameterized — ~35 ms each. The shaping applies the database option; on a database where the login may not, the fix is hugr-lab/mssql-extension#334, on the extension's 2.0 line.
  • Types stored as text in inlined data: floating point, nanosecond timestamps, 128-bit and unsigned 64-bit integers, intervals, enums, geometry and nested types are stored as text in the inlined-data tables — lossless, not filterable server-side (Writing). VARIANT columns are never inlined.
  • A rolled-back commit can leave an empty ducklake_inlined_data_* or ducklake_inlined_delete_* table behind — they are created outside the transaction so that the commit can see them; harmless, and ducklake_cleanup_old_files does not remove them. A flush leaves the emptied inlined tables in place — DuckLake's behaviour on every backend.
  • mssql_scan() inside a transaction must be the sole source of its query with mssql v0.2.5: a plan mixing it with a catalog scan fails depending on execution order. The manager follows the rule; a user query joining mssql_scan() against the lake inside a transaction may hit it. Fixed in the mssql extension's 2.0 line (#314).
  • Fabric Warehouse and Synapse dedicated pools cannot hold a catalog (Requirements).
  • No WebAssembly build — the mssql extension is raw TDS sockets.
  • Concurrent writers rely on DuckLake's retry loop. No writer loses a commit in the measured runs; the systemic alternative, SNAPSHOT isolation on the catalog connection, is proposed for the mssql extension (#331).