perf(segcache): load catalog in background to avoid blocking startup#757
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loadCatalog was called synchronously in NewSegmentCache, statting every cached segment on disk before the constructor returned. On a large cache this blocked the entire serve startup path for seconds to minutes. Move the load into Manager.Start as a third wg-tracked goroutine (mirroring the existing cleanupLoop/catalogFlushLoop split). NewSegmentCache now constructs only; LoadCatalog is exported so tests can call it synchronously. The merge loop now skips keys already present (a Put during load already wrote a newer entry and .seg file) instead of clobbering c.items, fixing the race that the old overwrite would have introduced.
The old message "Segment cache initialized" implied the catalog was warm. Now that the load runs in a background goroutine, reword to "Segment cache started (catalog loads in background)".
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@evulhotdog nice one, but don't you think that blocking the put while loading can cause cpu leak if there is a lot of put waiting to succed? maybe we should ignore the put while loading |
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@javi11 yeah, making it a no-op is probably easier to handle and reduces complexity. I was just trying to think about continuity and ensuring that we caching wherever we can. In general, altmount is a long running process, so this should be an edge case where you're streaming right away. I was just tired of waiting 5 minutes to load my cache each time, since it stat's each file! I simplified things, let me know what you think. |
javi11
reviewed
Jul 3, 2026
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@javi11 ready for ya again. |
javi11
reviewed
Jul 6, 2026
javi11
reviewed
Jul 6, 2026
Per review: the loading flag's lifecycle (set on entry, cleared on exit) now lives entirely in LoadCatalog. NewSegmentCache no longer pokes at load-state, so a cache can no longer be left permanently gating Puts if a future caller forgets to call LoadCatalog.
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Problem: Startup hangs while
loadCatalog()stats every cached segment on disk synchronously (oneos.Statper ~750KB segment, can be tens of thousands of calls).Fix: Moved catalog loading from the
NewSegmentCacheconstructor intoManager.Startas a background goroutine. Startup no longer blocks; the cache serves misses from Usenet until the catalog hydrates. Merge-under-lock prevents aPutduring load from being clobbered.