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Summary: POSIX semantics for LinkFile (hard links) allow linking a file that is still being written two, with both the source and destination showing any subsequent writes to the source. This may not be practical semantics for some FileSystem implementations such as remote storage. They might only link the flushed or sync-ed file contents at time of LinkFile, or might even have undefined behavior if LinkFile is called on a file still open for write (not yet "sealed"). This change builds on https://github.com/facebook/rocksdb/issues/12731 to bring more hygiene to our handling of WAL files in Checkpoint. Specifically, we now Close WAL files as soon as they are either (a) inactive and fully synced, or (b) inactive and obsolete (so maybe never fully synced), rather than letting Close() happen in handling obsolete files (maybe a background thread). This should not be a performance issue as Close() should be trivial cost relative to other IO ops, but just in case: * We don't Close() while holding a mutex, to avoid blocking, and * The old behavior is available with a new kill switch option `background_close_inactive_wals`. Stacked on https://github.com/facebook/rocksdb/issues/12731 Pull Request resolved: https://github.com/facebook/rocksdb/pull/12734 Test Plan: Extended existing unit test, especially adding a hygiene check to FaultInjectionTestFS to detect LinkFile() on a file still open for writes. FaultInjectionTestFS already has relevant tracking data, and tests can opt out of the new check, as in a smoke test I have left for the old, deprecated functionality `background_close_inactive_wals=true`. Also ran lengthy blackbox_crash_test to ensure the hygiene check is OK with the crash test. (The only place I can find we use LinkFile in production is Checkpoint.) Reviewed By: cbi42 Differential Revision: D58295284 Pulled By: pdillinger fbshipit-source-id: 64d90ed8477e2366c19eaf9c4c5ad60b82cac5c6 |
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