feat: Add async migration support - #470
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…ic base Drop _MigrationConfigBase and give MigrationConfig and AsyncMigrationConfig their own bodies. The shared base saved only a few trivial passthrough properties while adding generic indirection, and full duplication matches how Config/AsyncConfig are handled. MigrationConfig reverts to its pre-async standalone form.
Give MigratorBuilder and AsyncMigratorBuilder their own read_execution_order/ track_latency/track_errors methods instead of sharing a base for three trivial property setters. MigratorBuilder and types.py revert to their pre-async form.
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July 30, 2026 21:59
kinyoklion
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kinyoklion
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Move track_migration_op into a finally so a write cancelled mid-operation still emits its migration op event. The CancelledError propagates and no WriteResult is returned, but the event now records which origins were written, so a partial write is reported rather than lost. Reads are left as-is: a cancelled read has no side effect and loses its consistency measurement, so a partial read event carries no useful signal.
On an early cancel (before any origin write completes) OpTracker.build returned "no origins were invoked" and the client logged a spurious error. Guard the write finally with OpTracker.has_invocations so the event is only emitted when at least one origin ran. Drop the now-redundant finally comment.
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Replace the has_invocations guard with a warning logged when a migration write is cancelled before completion, and call track_migration_op unconditionally. A cancelled dual write is a torn write worth surfacing, and the warning is co-located with the client's build error on an early cancel. Revert the now-unused OpTracker.has_invocations accessor.
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Adds the async migration surface for the async Python SDK —
AsyncMigrator,AsyncMigratorBuilder,AsyncMigrationConfig, and theAsyncMigratorFntype — inldclient/migrations/async_migrator.py, eagerly exported fromldclient/migrations/__init__.py(import-cheap: asyncio stdlib only, no aiohttp).Also carries the migration config/builder dedup shared by the sync and async surfaces:
types.pygains_MigrationConfigBase[_MigratorFnT](Generic) and_MigratorBuilderBase(fluent-setter mixin), andmigrator.py'sMigratorBuilderis re-based onto that mixin. These are behavior-preserving refactors of already-released sync code.The public async classes carry experimental
.. caution::blocks.Self-contained: depends only on already-merged foundation work. The
AsyncLDClient/Contextreferences areTYPE_CHECKING-only (annotations kept lazy viafrom __future__ import annotations); no runtime import of any not-yet-merged async module.No CHANGELOG or version changes (handled at release).
Tracked internally: SDK-2767
Note
Medium Risk
New experimental migration execution path affects dual-origin reads/writes and telemetry during flag-driven cutovers; behavior is well-tested but not production-stable per API warnings.
Overview
Adds an experimental async migration API for the async Python SDK, mirroring the sync migrator’s stage-driven read/write behavior with coroutine-based old/new handlers.
New surface in
async_migrator.py:AsyncMigrator/AsyncMigratorImpl,AsyncMigratorBuilder,AsyncMigrationConfig,AsyncMigratorFn, andAsyncExecutor. Reads honorExecutionOrder(parallel, serial, random) viaasyncio.gatherand optional consistency checks; writes run authoritative-first and skip the second origin on authoritative failure.migration_variationis awaited;track_migration_opstays synchronous. Write cancellation logs a warning, still emits migration telemetry infinally, and propagatesCancelledErrorwithout undoing a completed authoritative write.ldclient/migrations/__init__.pyre-exports the new types.test_async_migrator.pyadds broad pytest coverage (builder validation, payloads, tracking, consistency, execution order, cancellation) using aFakeAsyncClient.Reviewed by Cursor Bugbot for commit d35a24c. Bugbot is set up for automated code reviews on this repo. Configure here.