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fix(SESF-79): bound the memory sync loop and report a stalled one - #81
Fixes SESF-79. During the DEVS-145 E.6 import on minitron, the memory sync task stopped finishing ticks for 24 minutes and left fts:minitron 452 records behind, with sync_error null and nothing in the log. A restart cleared it. py-spy showed idle executor threads and Postgres showed no lock, so the task was stuck on an await; the exact one is unknown because py-spy cannot see coroutine stacks.
Changes
Bounded passes (http_server.py): each reconcile and tick runs under SESSIONFLOW_MEMORY_TICK_TIMEOUT (default 600 s). On timeout the server logs every asyncio task's await chain, then cancels the work and records the timeout in /healthmemory.sync_error. The loop goes on.
Coroutine dump (http_server.py): format_async_tasks() follows cr_await from each task to the future it waits on. kill -USR1 <pid> logs it on demand.
Stale flag (http_server.py): /healthmemory.index gains last_tick_age_s and stale, true once the last finished tick is older than the timeout plus three sync intervals.
FTS first (memory_index.py): MemoryIndex.tick applies this host's FTS batch before the Milvus batch, so embedding cannot hold the keyword index back.
No duplicate Milvus work (memory_index.py, memory_store.py): _apply_milvus skips a record another server already acknowledged at this version and generation (MemoryStore.is_acked).
Docs: README env table, AGENTS.md and CLAUDE.md sync-loop note.
Tests
12 new tests, written first: 11 failed before the change; the newer-version guard already passed.
sync loop: tick and reconcile timeouts, error cleared after a good tick, the await chain in the log
format_async_tasks and the SIGUSR1 handler
/health stale and fresh, and before the first tick
index: FTS applied while the Milvus embed hangs; an already-indexed record is not embedded again; a newer version is still written
Full suite: 739 passed, 0 skipped, with the test DSNs set. ruff check . clean; Vale clean on the changed docs.
Not proven
The root await that hung is still unknown. With this change a repeat cancels itself within 10 minutes, logs where it waited, and shows up in /health.
Summary by CodeRabbit
Reliability
Memory indexing now processes local search updates before vector updates, so delays in vector processing don’t hold up local search.
Indexing passes have a configurable timeout, defaulting to 600 seconds. Timed-out work is cancelled, and syncing continues.
Monitoring
Health status reports sync errors and flags an index as stale when updates fall too far behind. Diagnostic task details are available on timeout or on demand.
Documentation
Added guidance on memory-sync timeouts, health reporting, and diagnostics.
During the DEVS-145 E.6 import on minitron the memory sync task stopped
finishing ticks at 19:50:33 UTC and stayed stuck until a restart at 20:14,
leaving fts:minitron 452 records behind. sync_error stayed null and nothing
was logged. py-spy showed every executor thread idle and Postgres showed no
lock or open transaction, so the task was suspended on an await that never
completed; py-spy cannot show coroutine stacks, so the exact await is unknown.
- Each reconcile and tick runs under SESSIONFLOW_MEMORY_TICK_TIMEOUT (600 s).
On timeout, every asyncio task's await chain is logged first, then the
work is cancelled and the timeout is recorded as sync_error. The loop
goes on.
- format_async_tasks() follows cr_await from each task to the future it
waits on; install_task_dump_handler() logs it on SIGUSR1 (installed in
lifespan), so the next stall can be read without a restart.
- /health memory.index gains last_tick_age_s and stale (older than the
tick timeout plus three sync intervals).
- MemoryIndex.tick applies this host's FTS batch before the Milvus batch,
so embedding cannot hold the keyword index back.
- _apply_milvus skips a record whose Milvus acknowledgement another server
already wrote for this version and generation (MemoryStore.is_acked),
instead of re-embedding the whole batch read at tick start.
Tests: 12 new (9 sync loop, dump and health; 3 index), written first; 11
failed before the change, the newer-version guard passed. Full suite 739
passed, 0 skipped; ruff clean; Vale clean on the docs.
Memory synchronization now processes FTS work before Milvus work and skips Milvus records already acknowledged by another server. The server applies configurable timeouts to sync operations, logs pending task chains on timeout, and reports sync errors and index staleness through health data.
Changes
Memory Index Synchronization
Layer / File(s)
Summary
Index batch ordering and acknowledgements memory_store.py, memory_index.py, tests/test_memory_index.py
MemoryStore.is_acked checks consumer acknowledgements. The index checks acknowledgements before Milvus writes and processes the FTS batch before the Milvus batch. Tests cover hanging embedding, acknowledged records, and newer versions.
Bounded sync and health reporting http_server.py, tests/test_fts_heal_worker.py, README.md, AGENTS.md, CLAUDE.md
Tick and reconcile operations use a configurable timeout. Timeout handling logs pending task chains, cancels work, and records a sync error. Health data reports tick age and staleness. Tests and documentation cover timeout recovery, task dumps, and health reporting.
sequenceDiagram
participant SyncLoop
participant BoundedRunner as _run_bounded
participant MemoryIndex
participant FTS
participant Milvus
participant HealthPayload
SyncLoop->>BoundedRunner: Run tick with configured timeout
BoundedRunner->>MemoryIndex: Start tick
MemoryIndex->>FTS: Apply pending FTS batch
MemoryIndex->>Milvus: Process Milvus batch
alt Tick times out
BoundedRunner->>MemoryIndex: Cancel tick
BoundedRunner-->>SyncLoop: Return timeout error
SyncLoop->>HealthPayload: Record memory.sync_error
end
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Possibly related PRs
lbruton/SessionFlow#78: Adds the memory store, per-consumer acknowledgements, memory index, and sync loop that this change updates.
Merge Risk: Moderate · previous review bea2f
Repeated sync stalls can delay indexing and, if database workers remain occupied, also stall memory search. Address retry spacing and the shared-worker risk before merging.
Pre-merge checks: 4
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The title clearly summarizes the main change: it bounds the memory sync loop and reports stalled synchronization.
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FTS moves first along the track Acknowledged records hold their place A bounded tick keeps watch on time Task chains surface when waits run long Health reports the index state Then sync begins another pass
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Actionable comments posted: 2
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Inline comments:
Review comments at @http_server.py:
- Line 609: In the memory sync flow around `_run_bounded` and `MemorySyncState`,
track when each reconcile attempt finishes, including failures, separately from
`last_reconcile`, which should continue to record successful reconciles only.
Skip a due reconcile during the retry cooldown after a recent attempt, while
allowing `tick()` to run. Update
`test_memory_sync_reconcile_timeout_still_ticks_and_stays_due` to verify the
cooldown skips a retry and the tick still runs.
- Around line 579-587: Update _run_bounded so timed-out memory sync calls cannot
repeatedly consume workers from the pool shared with memory search: isolate sync
work in its own executor or skip starting new sync work while uncancellable
calls remain in flight. Preserve the existing timeout behavior while ensuring
memory search retains access to its worker pool.
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Reviewing files that changed from the base of the PR and between 3b5aee5 and bea2f40.
Files selected for processing: 8
AGENTS.md
CLAUDE.md
README.md
http_server.py
memory_index.py
memory_store.py
tests/test_fts_heal_worker.py
tests/test_memory_index.py
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CodeRabbit review on #81:
- A timed-out run_db await is cancelled, but its memory-db thread keeps
running, so repeated timeouts could take every worker and stall search.
run_db now counts calls running on the store threads
(memory_store.db_calls_in_flight, DB_WORKERS = 4), and a sync pass is
skipped, with sync_error saying why, while three of the four are busy.
- A reconcile that failed or timed out was retried on every pass, so each
pass spent the full timeout before ticking. last_reconcile_attempt now
records every attempt; after a failure, passes only tick until
MEMORY_RECONCILE_RETRY_INTERVAL (300 s) has passed. last_reconcile still
records successes only.
Tests: 3 new (pause, no pause with one call in flight, the run_db
counter). test_memory_sync_reconcile_failure_still_ticks_and_stays_due now
advances its clock: inside the retry delay the pass only ticks, after it
the reconcile runs again. That test came from the #78 review fixes, not
the spec; D-23 only sets startup and every 6 hours. Full suite 742 passed,
0 skipped; ruff clean.
CodeRabbit review on #81: the attempt was stamped with the clock read
before the reconcile ran. A reconcile that times out at the default 600 s
is already older than the 300 s retry delay when stamped, so the next
pass retried at once. The attempt is now stamped with state.clock() after
it ends; on success last_reconcile takes the same value, which is how the
retry check tells success from failure.
Tests: 2 new (a slow failing reconcile is followed by a tick-only pass;
success leaves both stamps equal). Full suite 744 passed, 0 skipped; ruff
clean.
Codex review on #81: worker capacity was checked only at the start of a
pass. With two workers already held by timed-out calls, a reconcile that
also timed out inside run_db left a third busy, and the tick then took the
fourth, so search queued behind stuck calls. The check
(_store_workers_saturated) now runs again after the reconcile, and the
pass stops before the tick when all but one worker are busy, recording the
reconcile error and the pause.
Tests: 1 new (a reconcile that leaves a worker busy is not followed by a
tick). Full suite 745 passed, 0 skipped; ruff clean.
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Fixes SESF-79. During the DEVS-145 E.6 import on minitron, the memory sync task stopped finishing ticks for 24 minutes and left
fts:minitron452 records behind, withsync_errornull and nothing in the log. A restart cleared it. py-spy showed idle executor threads and Postgres showed no lock, so the task was stuck on anawait; the exact one is unknown because py-spy cannot see coroutine stacks.Changes
http_server.py): each reconcile and tick runs underSESSIONFLOW_MEMORY_TICK_TIMEOUT(default 600 s). On timeout the server logs every asyncio task's await chain, then cancels the work and records the timeout in/healthmemory.sync_error. The loop goes on.http_server.py):format_async_tasks()followscr_awaitfrom each task to the future it waits on.kill -USR1 <pid>logs it on demand.http_server.py):/healthmemory.indexgainslast_tick_age_sandstale, true once the last finished tick is older than the timeout plus three sync intervals.memory_index.py):MemoryIndex.tickapplies this host's FTS batch before the Milvus batch, so embedding cannot hold the keyword index back.memory_index.py,memory_store.py):_apply_milvusskips a record another server already acknowledged at this version and generation (MemoryStore.is_acked).Tests
format_async_tasksand the SIGUSR1 handler/healthstale and fresh, and before the first tickruff check .clean; Vale clean on the changed docs.Not proven
The root
awaitthat hung is still unknown. With this change a repeat cancels itself within 10 minutes, logs where it waited, and shows up in/health.Summary by CodeRabbit