mirror of
https://github.com/microsoft/BCQuality.git
synced 2026-10-05 14:46:55 +01:00
2b5550c346
Lead with a complete plugin quick start and add task-oriented usage, troubleshooting, customization, and contribution guides. Preserve the broader plugin framing, correct conflicting contract guidance, support Agents folder reviews, and align repository validation. Convert existing sample references to clickable links without changing knowledge rules. Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
26 lines
1.6 KiB
Markdown
26 lines
1.6 KiB
Markdown
---
|
|
bc-version: [all]
|
|
domain: performance
|
|
keywords: [readisolation, locktable, updlock, read-only, transaction-scope, isolation-level]
|
|
technologies: [al]
|
|
countries: [w1]
|
|
application-area: [all]
|
|
---
|
|
|
|
# Prefer ReadIsolation over LockTable for read-only scenarios
|
|
|
|
## Description
|
|
|
|
Without read scale-out, `LockTable` causes subsequent reads of that table in the transaction to use `UPDLOCK`. With read scale-out, those reads use `REPEATABLEREAD` on the replica instead. `ReadIsolation` selects an isolation level for one record instance. A helper that only reads should not broaden locking for the table merely to request committed data.
|
|
|
|
## Best Practice
|
|
|
|
For a read-only operation that specifically requires committed data, set `Rec.ReadIsolation := IsolationLevel::ReadCommitted` immediately before the read. If the default isolation is sufficient, set neither property. `ReadCommitted` can still block behind writers and does not guarantee that repeated reads stay unchanged; use the isolation level required by the operation. Reserve update locks for read-before-write logic, not read-only helpers.
|
|
|
|
See sample: [`prefer-readisolation-over-locktable-for-reads.good.al`](prefer-readisolation-over-locktable-for-reads.good.al).
|
|
|
|
## Anti Pattern
|
|
|
|
`Rec.LockTable();` at the top of a helper that only reads, perhaps to "make sure the read is consistent". It takes stronger isolation than the helper needs and changes later reads of that table in the surrounding transaction or read-scale-out session.
|
|
|
|
See sample: [`prefer-readisolation-over-locktable-for-reads.bad.al`](prefer-readisolation-over-locktable-for-reads.bad.al).
|