Document migration locking

[Copilot]

EF Core 9 introduced a migration locking mechanism (dotnet/efcore#34115, dotnet/efcore#34338) that was never properly documented. The aka.ms/efcore-docs-migrations-lock link had no target content.

New section in applying.md: Migration locking

• When it applies: dotnet ef database update, Update-Database, bundles, MigrateAsync()/Migrate() — not SQL scripts
• Provider-specific warning: A [!WARNING] block alerts readers that locking varies across providers and can involve provider-specific issues (e.g. SQLite abandoned locks)
• Limitations: Concise bullet list noting that wrapping MigrateAsync in an explicit transaction is not supported (links to the EF9 breaking change note) and that SQLite abandoned locks can block subsequent migrations (links to SQLite limitations)

SQLite limitations (sqlite/limitations.md): Expanded "Concurrent migrations protection"

• How the lock works: SQLite uses __EFMigrationsLock table (vs. SQL Server's session-level sp_getapplock)
• Handling abandoned locks: Lock rows can survive process termination — documented both fixes:

DROP TABLE "__EFMigrationsLock";
-- or
DELETE FROM "__EFMigrationsLock";

Cross-reference updates

• data-seeding.md: migration locking link now points to new section instead of whatsnew
• whatsnew.md (EF9): added forward link to new docs

[Copilot]

Pull request overview

Adds missing EF Core 9 documentation for the migrations concurrency/locking mechanism (the previously un-targeted aka.ms/efcore-docs-migrations-lock concept), and updates related pages to cross-reference the new authoritative section.

Changes:

• Add a new Migration locking section to the “Applying migrations” documentation, including provider-specific behavior (SQL Server vs SQLite), abandoned-lock remediation, and explicit-transaction interaction.
• Update cross-references in EF9 “What’s New”, SQLite limitations, and data seeding docs to point to the new section.
• Add SQLite guidance (including a SQL snippet) for clearing abandoned migration locks.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
entity-framework/core/what-is-new/ef-core-9.0/whatsnew.md	Adds a forward link from the EF9 release notes to the new migration locking documentation section.
entity-framework/core/providers/sqlite/limitations.md	Updates the SQLite “Concurrent migrations protection” section to reference the new docs and includes a remediation SQL snippet.
entity-framework/core/modeling/data-seeding.md	Updates the seeding docs to reference migration locking via the new canonical link.
entity-framework/core/managing-schemas/migrations/applying.md	Introduces the new “Migration locking” documentation section with details, examples, and mitigation guidance.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[roji]

LGTM but see comments/suggestions.