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Operations Notes

Concurrency Model

excel-dbapi assumes a single writer per workbook path.

  • Safe pattern: one process writes, many can read snapshots.
  • Unsafe pattern: multiple concurrent writers to the same .xlsx file.

If multiple writers are required, coordinate with an external lock.

Engine Tradeoffs

openpyxl engine (default)

  • Better workbook fidelity for most classroom/business spreadsheets.
  • Good default for mixed read/write workloads.
  • Loads with data_only=True — formulas are evaluated to their cached values.

pandas engine

  • Convenient for DataFrame-heavy flows.
  • Rewrites the workbook and may drop rich formatting, formulas, and charts.

File Integrity Semantics

Saves are performed with a temp file followed by os.replace(...). This provides atomic replacement on supported filesystems and avoids partial writes in normal failure scenarios.

Transaction Semantics

  • autocommit=True (default): Changes are saved to disk after each execute(). rollback() raises NotSupportedError.
  • autocommit=False: Changes are held in memory. commit() flushes to disk. rollback() restores the in-memory snapshot taken at connection open or last commit().

This is not ACID — there is no write-ahead log or crash recovery.