Write cached responses atomically#491
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Every request that renders a cacheable page writes the response body to the same cache file, so under concurrent requests for one page the losers fail with "resource busy (file is locked)" and are served a 500 - the behaviour reported in #482, where a homepage flood turned a third of responses into errors. A half-written file was also briefly visible to nginx, which serves the cache directory directly. The response is now written to a temporary file (suffixed with the writing thread's id, so concurrent writers cannot collide on that name either) and renamed into place, which is atomic. Under the same 400-connection homepage flood, every response is now a 200.
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Every request that renders a cacheable page writes the response body to the same cache file, so concurrent requests for one page race and the losers fail with
resource busy (file is locked)and are served a 500.@flip111 tracked this down in #482 — hitting the homepage with 400 connections caused about a third of responses to produce 500s, each paired with the
withBinaryFile: resource busyerror. The response is now written to a temporary file and renamed into place, which is atomic.Verified using the same approach as @flip111; all ~3600 responses are 200s without errors, the cache file looks correct, and no temp files are left behind.