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perf(metadata): scale image-cache concurrency with host CPUs - #817
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The scheduled image-cache task ran 2 workers on a 2-job claim page, regardless of hardware — measured at roughly 60 images/minute on a ~600k-item library, where the queue takes days to drain after a large scan. processClaimedJobs already dispatches a claimed page through a bounded semaphore, so a page larger than the worker count keeps the pool saturated instead of waiting on every straggler before the next page can be claimed; the tiny fixed numbers were the only thing holding throughput back. Workers now scale as 4x GOMAXPROCS capped at 48 — each job is a mix of a 30s-capped download and a libvips encode ladder, so oversubscribing CPUs keeps cores busy during network waits, while the cap keeps a many-core server from monopolizing provider connections and household boxes at a modest pool instead of a fixed 48. The claim page is 10 jobs per worker: it drains within ten times the worst single job, well inside the 15-minute claim lease and behind the existing 10-minute task runtime cap. Derived from RXWatcher/silo-server@3b377f5c2, which measured roughly 2,900 images/minute with 48 workers over a 60-minute window on the library above; that change hard-coded 480/48, which fits a large server but oversubscribes the small end of deployments. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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📝 WalkthroughWalkthroughThe image-cache system now exports its lease duration, applies a two-minute timeout to each job, and sizes workers from CPU and memory limits. Claim capacity and tests now use the dynamic worker configuration. ChangesImage-cache runtime controls
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟠 High · up to Dynamic image-cache concurrency can exceed a container’s actual memory limit, causing OOM termination and interrupting metadata processing. Merge should wait until all detected memory limits are honored and low-memory hosts can run with a single worker. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Review follow-ups on the concurrency raise (#817): Lease enforcement: only the download had a deadline; a hung encode or upload could hold a job indefinitely, so nothing enforced the claim-page lease math and an unstarted page tail could outlive its 15-minute lease and be reclaimed and duplicated by another node. Every job now runs under ImageCacheJobTimeout (2 minutes) end to end, the claim page drops from 10 to 5 jobs per worker so a page's worst-case drain is 10 minutes against the 15-minute lease, and the arithmetic is asserted in TestImageCacheWorkerCount against the now-exported ImageCacheLeaseDuration. Memory bound: worker count derived from CPUs alone could put 48 concurrent jobs — each able to hold a 25 MiB download plus a full Go decode of the original for thumbhash — inside a container with a small memory limit. The pool is now also capped at one worker per 512 MiB of the tightest detectable memory bound (GOMEMLIMIT, cgroup limit, then /proc/meminfo), with the original pool of 2 as the floor. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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In `@internal/taskmanager/tasks/cache_metadata_images.go`:
- Around line 49-53: Update detectImageCacheMemoryBytes to collect every valid
memory limit, including GOMEMLIMIT and cgroup limits, and return the smallest
value rather than preferring one source. In imageCacheWorkerCount, remove the
unconditional two-worker floor so limits below two imageCacheWorkerMemoryBudget
units can select one worker, while retaining the existing CPU and upper-bound
calculations. Add tests covering conflicting limits and sub-1 GiB memory limits.
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📒 Files selected for processing (5)
internal/metadata/image_cache_job_repo.gointernal/metadata/image_cache_processor.gointernal/metadata/image_cache_processor_test.gointernal/taskmanager/tasks/cache_metadata_images.gointernal/taskmanager/tasks/cache_metadata_images_test.go
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Two more review follow-ups on the image-cache sizing (#817): Cgroup limits: worker sizing consulted only the root-level cgroup memory files, which are right inside a namespaced container but wrong for a systemd unit with MemoryMax= or a leaf inheriting a tighter slice/pod limit — those fell through to host MemTotal and could size 48 workers inside a small cgroup. nodemetrics already resolves this process's own cgroup and walks its ancestors for the sampler; that machinery is now exposed as nodemetrics.EffectiveMemoryLimitBytes and used for sizing, with a fixture test covering the systemd-slice shape. Overshoot: the per-job context timeout cannot preempt the synchronous decode/encode segment (imageutil.Thumbhash and GenerateVariants take no context), so the two-minute bound is not perfectly hard — the job stops at the next context-aware step. That segment works on inputs capped at 25 MiB, so its overshoot is CPU-bounded; the claim page drops from 5 to 4 jobs per worker, keeping the worst chain inside the lease with nearly two minutes of overshoot allowance per job, and the sizing test now requires that headroom instead of a bare drain < lease check. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Review follow-up: detection preferred GOMEMLIMIT outright, so a GOMEMLIMIT set looser than a tight cgroup limit would size workers past what the container can hold. All sources — GOMEMLIMIT, the effective cgroup limit, host memory — are now consulted and the smallest positive one wins, with the min logic extracted and unit-tested alongside new sub-1GiB sizing cases. The floor of 2 workers is kept deliberately: a sub-1GiB deployment already ran 2 workers before this branch, so the floor preserves the shipped baseline rather than regressing below it. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Review follow-up: below 2x the per-worker budget the floor of 2 wins, which is deliberate — a sub-1GiB deployment ran 2 workers before this sizing existed, so the memory cap never reduces a host below its long-standing baseline. Say so on the function instead of leaving the budget to read as a guarantee. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Problem
The scheduled
cache_metadata_imagestask runs 2 workers on a 2-job claim page regardless of hardware. On a ~600k-item library that measured roughly 60 images/minute — the queue takes days to drain after a large scan while artwork sits missing in every client.The 2/2 sizing predates
processClaimedJobsdispatching a claimed page through a bounded semaphore. With the semaphore, a page larger than the worker count keeps the pool saturated instead of waiting on every straggler before the next page can be claimed; the tiny fixed constants were the only thing holding throughput back.Change
Derived from RXWatcher/silo-server@3b377f5, which measured roughly 2,900 images/minute with 48 workers over a 60-minute window on the library above. That commit hard-codes 480/48, which fits a large server but oversubscribes the small end of Silo's deployment spectrum, so this PR scales instead of copying:
min(48, 4 × GOMAXPROCS), additionally capped by memory. Each job is a mix of a 30-second-capped download and a libvips WEBP encode ladder, so oversubscribing CPUs keeps cores busy during network waits. The cap keeps a many-core server from monopolizing provider connections; themax(numCPU, 1)floor gives even a 1-core box 4 workers — still double the old fixed pool. A 4-core household box gets 16; a 12-core server reaches the measured 48.metadata.ImageCacheLeaseDuration) is the ceiling on page size. Review caught that nothing bounded a job end to end — only the download had a deadline — so every job now runs undermetadata.ImageCacheJobTimeout(2 minutes) inprocessClaimedJobs. That context cannot preempt the synchronous decode/encode segment (also caught in review), but that segment is CPU-bounded on inputs capped at 25 MiB, so the page is sized at 4 × 2 = 8 minutes of timeout-based drain plus nearly two minutes of overshoot allowance per job, inside the 15-minute lease. The sizing test requires that headroom explicitly.nodemetrics.EffectiveMemoryLimitBytes(own cgroup, ancestors, root — so a systemdMemoryMax=or inherited pod/slice limit binds, not just a namespaced container's root files), and/proc/meminfo— and the smallest positive one wins. The floor of 2 workers preserves the shipped baseline; sub-1GiB deployments ran 2 workers before this PR too. The thumbhash full-resolution decode itself is being filed separately; it is shared change-detection state with ebook scans and does not belong in this PR.Tests
TestImageCacheWorkerCount— CPU scaling curve, memory-capped cases, and the lease invariant: jobs-per-worker ×ImageCacheJobTimeoutplus a 50% overshoot budget must fit insideImageCacheLeaseDuration.TestEffectiveMemoryLimitBytesFindsTheBindingAncestor— fixture test for the systemd-slice shape: limit on the slice binds while leaf and root readmax; a tighter leaf wins; all-maxreads as no limit.claimLimit = 2/concurrency = 2and now assert against the shared sizing vars, which is what they were checking all along — thatExecutepasses the task's configured page and pool through to the runner.Validation
go test ./internal/taskmanager/... ./internal/metadata/ ./internal/nodemetrics/— passesgo build ./...,go vet ./...,gofmt -lcleangolangci-lint run --new-from-merge-base=origin/main ./...— 0 issuesRelated issue: N/A — narrow fix (task sizing, a per-job timeout, and an internal memory-limit helper; no API, client, or jellycompat surface changes)
AI Disclosure
processOne→imagecache(30s download timeout, 25MB download cap, libvips encode) to confirm the lease arithmetic, and the fixed worker count was rejected for small hosts in favor of CPU scaling. The two existing tests that encoded the old sizing were updated deliberately, not silenced.🤖 Generated with Claude Code