fix(web-search): serialize extraction and return its retained heap - #571
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A gateway with web-search intercept enabled sat at a near constant 533MB RSS (518MB of it anonymous) against a 273MB freshly started floor. Two separate faults in the extraction path, both found by driving the real WebSearchBackend over local copies of real pages. Retained heap. Each search parses up to max_results pages of HTML through libxml2, whose allocations are large enough that glibc keeps the freed chunks in its arenas instead of returning them. The resident set climbs to a high-water mark and parks there, which reads as a leak even though nothing is reachable: one search alone added 178MB, and a single malloc_trim handed 154MB straight back. gateway.heap.release_free_heap now runs after each search's extraction batch. Over 24 searches this holds the process at ~148MB instead of ~300MB. It no-ops off glibc, so musl and macOS are unaffected. Process aborts. trafilatura is not thread-safe, and the backend called it from five threads at once. The same 24-search loop died with a glibc "double free or corruption" in 4 of 12 runs, with and without the trim. Extraction is now serialized on a module-level lock: 12 of 12 runs clean. This is not free, since lxml drops the GIL and extraction genuinely ran in parallel; a search over five heavy pages went from roughly 520ms to roughly 880ms. Aborting the process takes every in-flight request with it, so the latency is the better trade. Worth reporting upstream. Also fixes two things found along the way: * file_extractors built a MarkItDown per call, and each one initializes magika, loading an ONNX model and starting an inference thread pool that is never released. That cost ~5MB and 9 threads per extraction, growing without bound. It is now built once behind a lock, since racing callers would otherwise each build their own. * /metrics carried no process memory at all, because the gateway keeps its own registry rather than prometheus_client's default one. Registering ProcessCollector exposes process_resident_memory_bytes, so this is visible on a graph instead of needing a shell inside the container. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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WalkthroughThe gateway adds best-effort heap trimming and process metrics. File extraction reuses one thread-safe MarkItDown converter. Web search serializes trafilatura extraction and releases free heap after successful or failed enrichment. Unit tests cover concurrency and failure paths. ChangesGateway resource and extraction controls
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… pool Review follow-ups on the extraction path. Serializing on a lock inside asyncio.to_thread held threads in the loop's default executor while they waited. That pool is shared with file extraction, PDF rasterizing and OCR, so a queue of searches stalled unrelated uploads behind it: an unrelated to_thread task took 2267ms to start, against 0.3ms with a dedicated worker. Extraction now runs on its own single-worker executor, which gives the same serialization while occupying one thread. Also: * _get_converter moved outside _extract_sync's try, which turned a magika model-load failure from a failed extraction into an exception escaping extract_text_from_file. That is caught upstream, but it abandons normalization for the whole request and skips the scanned-PDF rasterize fallback. Restored to a failed extraction. * test_metrics_expose_process_memory asserted on ProcessCollector output, which is empty without /proc, so it failed off Linux. Guarded like the equivalent test in test_heap.py. * Dropped the measured figures from the extraction comment. They are corpus-dependent and no reader can check them; the mechanism stays. * _get_converter's docstring said magika's threads are never released. They return when the instance is collected; the memory does not. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Inline comments:
In `@tests/unit/test_heap.py`:
- Around line 46-49: Update the skip condition on
test_malloc_trim_resolves_on_linux to skip when platform.libc_ver()[0] is not
"glibc", covering both non-Linux and musl environments while retaining the
assertion for glibc Linux.
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src/gateway/heap.pysrc/gateway/metrics.pysrc/gateway/services/file_extractors.pysrc/gateway/services/web_search_backend.pytests/unit/test_file_extractors.pytests/unit/test_gateway_metrics.pytests/unit/test_heap.pytests/unit/test_web_search_backend.py
gateway.heap treats a libc without malloc_trim as a deliberate no-op, but the guard only checked for Linux, so the assertion would fail on Alpine. CI runs a Debian-based image, so it would only have bitten someone running the suite on musl. Reported by CodeRabbit. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Description
A gateway with web-search intercept sat at a near constant 533MB RSS (518MB of it anonymous) against a 273MB freshly started floor. Driving the real
WebSearchBackendover local copies of real pages found two faults in the extraction path.Retained heap. Each search parses up to
max_resultspages of HTML through libxml2, whose allocations are large enough that glibc keeps the freed chunks rather than returning them. One search alone added 178MB, and a singlemalloc_trimhanded 154MB back, so nothing was reachable.gateway.heap.release_free_heapnow runs after each search's extraction batch: over 24 searches the process holds at ~148MB instead of ~300MB, and it stays flat under sustained load. No-ops off glibc, so musl and macOS are unaffected.Process aborts. trafilatura is not thread-safe: it parses through lxml parsers held in its own module globals, and the backend called it from five threads at once. A 24-search loop over real pages died with a glibc
double free or corruptionin a minority of runs, independently of the trim. Extraction now runs on a dedicated single-worker executor, which serializes it: 12 of 12 runs clean.A dedicated executor rather than a lock around
asyncio.to_thread, because the default pool is shared with file extraction, PDF rasterizing and OCR; threads blocked on a lock still hold their slot, so queued searches stalled unrelated uploads behind them (2267ms versus 0.3ms for an unrelated task). Serializing costs throughput, since lxml drops the GIL and extraction genuinely ran in parallel. An abort takes every in-flight request with it, so that is the better trade.Two things found along the way:
file_extractorsbuilt aMarkItDownper call. Each initializes magika, loading an ONNX model plus an inference thread pool: ~5MB and 9 threads per extraction, and the memory never came back. Now built once behind a lock, since racing callers would otherwise each build their own./metricsexposed no process memory, because the gateway keeps its own registry rather than prometheus_client's default.ProcessCollectoraddsprocess_resident_memory_bytes.Measured on aarch64; absolute figures will differ on amd64.
Moving extraction into worker processes was prototyped and rejected for now: CPython's
max_tasks_per_childdeadlocks when multi-megabyte payloads back up the call queue, and the workarounds cost more memory than they saved (roughly 478MB under saturation against 235MB here). The version worth building instead has workers fetch their own URLs so only URLs cross the pipe, which is a security-sensitive change to the SSRF and redirect handling and belongs in its own PR.PR Type
Relevant issues
None filed; found while investigating memory use on a Railway deployment.
Checklist
tests/unit,tests/integration).make lint,make typecheck,make test).make openapi-checkpasses.AI Usage
AI Model/Tool used:
Claude Opus 5, via the Claude Code CLI.
Any additional AI details you'd like to share:
The diagnosis came from measurement rather than inspection: process RSS split into anonymous versus file-backed, per-dependency import cost, and A/B runs of the real backend against a local corpus of real pages. Several conclusions drawn along the way were wrong and were corrected by later measurement.
MALLOC_ARENA_MAX=2looked worth ~100MB in a synthetic harness but only ~22MB on the real path, so it is not here. The concurrency abort was briefly dismissed after a single run survived, which was a false negative from one sample. An independent review then caught that the first version of the serialization starved the shared executor, and that moving the converter build outside itstryhad turned a model-load failure into an exception escaping the extractor.Note: this PR was drafted by Claude Opus 5 via back-and-forth with @njbrake. The reasoning and decisions are his; the prose is Claude's.
Summary
MarkItDowninstance across extraction requests./metrics.These changes reduce memory retention and prevent extraction work from blocking unrelated tasks.