addenergyx opened a new pull request, #39384:
URL: https://github.com/apache/beam/pull/39384
Fixes #39383
**The bug.** `GlobalCachingStateHandler.blocking_get` caches partially
materialized bag state as a `ContinuationIterable` across bundles, keyed by the
user-state cache token. The iterable's lazy remainder holds the continuation
token minted by the read that created it
(`functools.partial(self._lazy_iterator, state_key, coder,
continuation_token)`).
Continuation tokens can become permanently invalid — e.g. Dataflow revokes
them together with the work item that created them ("work token no longer valid
on the backend"). When that happens, iterating the cached object raises, but
nothing invalidates the cache entry: the user-state cache token is unchanged,
so every subsequent bundle reading that state cell is served the same poisoned
object and replays the dead token. A fresh read would succeed, but never
happens. The stage retries forever and its watermark stalls.
Observed in production on Dataflow (Python streaming, Streaming Engine,
Runner v2, Beam 2.74.0) with a stateful transform whose bag state exceeded one
page: unbounded "work token no longer valid" retry storms wedging the stage;
disappears when state stays under one page (no continuation token → plain list
cached → unreachable code path).
**The fix.** Invalidate the cache entry when iterating the continuation
fails, so the next read loads fresh state. Under transient failures this costs
one extra reload; under permanent token invalidation it is the difference
between self-healing and an infinite retry storm. The change is backward
compatible: `ContinuationIterable.on_failure` defaults to `None`, and
`_partially_cached_iterable` behaves as before when no cache key is passed.
**Validation.** The new regression test
`CachingStateHandlerTest.test_failed_continuation_invalidates_cached_iterable`
is a deterministic unit repro (no Dataflow required): it uses a state-handler
fake with epoch-scoped token revocation, so revoked tokens fail while fresh
reads succeed — matching real runner semantics.
- RED (without the fix): the test fails — the second bundle's read is served
the cached iterable and raises `RuntimeError: continuation token no longer
valid` from the dead token.
- GREEN (with the fix): the full `sdk_worker_test.py` passes (including all
pre-existing tests), and `statecache_test.py` passes unchanged — 35 passed
across both files.
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