bcquality/microsoft/knowledge/performance/keep-event-subscribers-lightweight.md

bc-version	domain	keywords	technologies	countries	application-area
all	performance	event subscriber publisher extension	al	w1	all

Keep event subscribers lightweight

Contributions welcome — open a PR to refine or extend this article.

Description

Event subscribers run synchronously on the publisher's thread. If a subscriber does heavy work — a database query, a web service call, a layout render — every caller of the publisher pays that cost. Subscribers on hot events (OnAfterValidate on common fields, OnBeforeInsert on ledger-entry-like tables) can multiply a small per-call cost into a system-wide regression.

Best Practice

Keep subscribers small: guard early with inexpensive checks on the publisher record before doing any database work, defer heavy work to a task queue or a background session, and cache results across invocations when the data is stable. In hot events, a cheap Type/Status/IsTemporary exit before a Get or FindFirst is often the difference between a rare lookup and an N+1 query across every posted line.

See sample: keep-event-subscribers-lightweight.good.al.

Anti Pattern

Calling an external web service, running a report, or iterating a large table from inside an event subscriber on a hot publisher makes every operation on that publisher as slow as the heaviest subscriber.

See sample: keep-event-subscribers-lightweight.bad.al.