`_try_acquire_file_lock` opened the lock file with `open(mode='w')`
BEFORE the mtime check, which truncated the file and refreshed mtime
to now. The subsequent age check always saw ~0, so the TTL reclaim
branch was never reachable and `materialize.lock_ttl_seconds` was
a silently no-op config knob.
Repro:
before open(w): mtime age = 100000s
after open(w): mtime age = 0s
Fix: stat the lock path BEFORE any open(). If pre-probe mtime is
older than TTL, unlink (forcing a fresh inode for the open + flock
that follows). Order is now stat-then-decide-then-probe, not
probe-then-stat-then-decide.
Two regression tests added in tests/test_bq_materialize_concurrency.py:
- test_stale_held_lock_is_reclaimed_despite_live_holder — exercises
the full reclaim path with a still-living fcntl holder. Pre-fix
this returned None (in_flight forever); post-fix returns a holder
fd on a new inode.
- test_failed_probe_does_not_self_refresh_lock_mtime — sister test
pins that a failed acquisition's mode='w' truncate doesn't
pathologically loop.
Residual cross-process risk (genuinely overrunning materialize past
TTL races a fresh attempt — both write to the same parquet.tmp,
inode-level flock independence means new acquisition succeeds while
old holder is still alive) stays documented in the helper docstring.
In-process threading.Lock keyed on table_id blocks the single-process
race; cross-process protection relies on TTL being well above
longest plausible COPY (24h default).
- extractor._try_acquire_file_lock: close fd and re-raise on non-
BlockingIOError from fcntl.flock (read-only fs, unsupported flock,
fd exhaustion). Pre-fix the fd leaked silently and the underlying
OSError still propagated past the caller.
- extractor: reorder module-level layout so logger is bound before
the new lock-related helpers reference it. Deferred import of
app.instance_config inside _get_lock_ttl_seconds documented inline.
- extractor: comment _table_locks unbounded-by-design rationale.
- tests: docstring + monkeypatch-target rationale for the two
concurrency tests where the contract isn't obvious from the body.
Two layers of concurrency control. Layer 1 is a per-table_id
threading.Lock keyed on table_id; Layer 2 is fcntl.flock on a sibling
<id>.parquet.lock file. Overlapping calls for the same id raise
MaterializeInFlightError, which the caller treats as 'skipped,
in_flight' instead of a hard error. Stale file locks (mtime older
than materialize.lock_ttl_seconds, default 86400) are reclaimed on
the next attempt — covers the rare case where a holder was hard-killed
before kernel-level flock release.
Pre-fix, when a materialize ran longer than the scheduler tick interval
(15 min), the next tick called materialize_query for the same id, hit
the unconditional tmp_path.unlink() at function entry, and started a
second COPY against the same path. Both writers interleaved bytes;
the original COPY's read_parquet validation then failed with
'No magic bytes found at end of file'.
