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Do not Commit inside loops
Contributions welcome — open a PR to refine or extend this article.
Description
Commit ends the current write transaction. Calling it inside a per-row loop usually produces one transaction per iteration and loses the ability to roll back the whole operation atomically; it also interferes with batching. Most loops need no explicit Commit at all — AL auto-commits the enclosing code module on successful completion (see understand-implicit-transaction-boundary.md).
A durability checkpoint inside an outer batch loop can be valid only when the same transaction persists a progress marker or state that makes retries strictly exclude completed work, the checkpoint follows a complete business unit, and errors propagate instead of being swallowed. Restart safety and bounded retrieval are separate requirements: a persisted watermark can make retries safe, but an outer FindSet over the full remaining tail with periodic commits still retrieves the complete set because FindSet is not implemented as TOP X.
Best Practice
If the batch is large enough that a single transaction is untenable, use an ordered primary-key watermark and retrieve a bounded next-N key list. The sample uses a query capped by TopNumberOfRows to fill a temporary key buffer, then takes update locks and modifies only those exact keys. It does not reconstruct an inclusive first-to-last range that concurrent inserts could expand. Persist the last selected key in the same transaction as the completed chunk, then commit after the bounded helper returns. Use a stable key and define how a later run handles records inserted at or below an already committed watermark. Let errors escape so failed work is not recorded as complete. A Codeunit.Run boundary can also own a chunk when its implicit commit and error behavior fit the caller — see codeunit-run-as-atomic-sub-operation.md.
See sample: avoid-commit-inside-loops.good.al.
Anti Pattern
Placing Commit inside repeat ... until Next() = 0 without persisted progress is almost always a mistake: retries re-enter already committed work, while the cost of starting a transaction on every row dominates the operation. A progress variable held only in memory is not restart-safe. A full-tail FindSet with a commit every N rows is not bounded retrieval, even if a persisted watermark makes it restart-safe. A capped query that discovers only an upper key and then re-reads an inclusive key range is not exact batching either; concurrent inserts inside that range can enlarge the checkpoint.
See sample: avoid-commit-inside-loops.bad.al.