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Mai Huy HoàngandClaude Opus 5
53ffd7fc02
A cache-restored tree is a farm of symlinks into the shared CAS. Writing it is cheap, but walking it is not: resolving each link reads an inode out of a directory far too large to stay in the OS metadata cache. Measured against a 57 GB / 952k-blob CAS, a cold stat of a CAS blob costs 165 us against 3.6 us for a regular file, which makes a cold classpath walk of a restored tree roughly 38x slower than one of real files. On an 81-module build with exportJars, a no-op compile drops from 14.75s to 5.96s once the tree is real files. DiskActionCacheStore now seeds the existing symlinkSupported latch from the filesystem holding the CAS, and materializes entries with copyFile on APFS. Files.copy reaches clonefile(2) there, so each entry gets its own inode and walks at full speed while its data blocks stay shared with the CAS: the restored tree measured 11 MB against 137 MB for the symlinked one. Copies also cannot corrupt a blob when a task overwrites its output, which a symlink into the CAS can. On every other filesystem the behavior is unchanged. Co-authored-by: Claude Opus 5 (1M context) <[email protected]>