Reject high-cost requests instead of creating more OS threads when overloaded #639
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We have been using a file removal semaphore with weight 5,000 (half of Go's default 10,000 maximum OS threads, beyond which Go will crash), in an attempt to avoid crashing when the filesystem/storage layer can't keep up with our requirements.
This change renames that semaphore to
diskWaitSem
and also uses it for disk-write operations. When the semaphore cannot be acquired for disk-writes, we return HTTP 503 (service unavailable) or gRPC RESOURCE_EXHAUSTED error codes to the client.Relates to #638