Nic Cope 7a2c6a432f Use checksums instead of fsyncs to manage discovery cache corruption ... Part of the API discovery cache uses an HTTP RoundTripper that transparently caches responses to disk. The upstream implementation of the disk cache is hard coded to call Sync() on every file it writes. This has noticably poor performance on modern Macs, which ask their disk controllers to flush all the way to persistant storage because Go uses the `F_FULLFSYNC` fnctl. Apple recommends minimizing this behaviour in order to avoid degrading performance and increasing disk wear. The content of the discovery cache is not critical; it is indeed just a cache and can be recreated by hitting the API servers' discovery endpoints. This commit replaces upstream httpcache's diskcache implementation with a similar implementation that can use CRC-32 checksums to detect corrupted cache entries at read-time. When such an entry is detected (e.g. because it was only partially flushed to permanent storage before the host lost power) the cache will report a miss. This causes httpcache to fall back to its underlying HTTP transport (i.e. the real API server) and re-cache the resulting value. Apart from adding CRC-32 checksums and avoiding calling fsync this implementation differs from upstream httpcache's diskcache package in that it uses FNV-32a hashes rather than MD5 hashes of cache keys in order to generate filenames. Signed-off-by: Nic Cope <nicc@rk0n.org>		2022-07-27 00:13:30 -07:00
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httpcache	Use checksums instead of fsyncs to manage discovery cache corruption	2022-07-27 00:13:30 -07:00