bcquality/microsoft/knowledge/events/do-not-publish-events-inside-loops.md

bc-version	domain	keywords	technologies	countries	application-area
all	events	performance loops event-publishing batch onbefore onafter subscriber-cost	al	w1	all

Do not publish events inside loops

Description

Raising an event on every iteration of a loop multiplies the cost of every subscriber by the number of records. A subscriber doing even a little work per call can turn a fast batch into a timeout when the loop runs over thousands of rows, and the publisher has no control over how expensive a subscriber is. Unless a genuine per-row hook is required, publish once before the loop and once after it, passing enough context — filters, a key, or a buffer — for subscribers to act on the whole set at once. Generated code tends to drop an event inside the repeat … until without weighing the per-iteration multiplier.

Best Practice

Raise OnBeforeProcessLines before the loop and OnAfterProcessLines after it, outside the repeat … until, so each subscriber runs once per batch rather than once per row. Give those events the record or filters they need to operate on the whole set.

See sample: do-not-publish-events-inside-loops.good.al.

Anti Pattern

An event raised inside the loop body, fired once per iteration, so subscriber cost scales with the row count and large batches slow down or time out. Detection: an OnBefore…/OnAfter…/On… raise located between repeat and until in a record loop.

See sample: do-not-publish-events-inside-loops.bad.al.