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By default, the GCS Go packages have an internal "chunk size" of 8MB, used for blob uploads. Media().Do() will buffer a full 8MB from the io.Reader (or less if EOF is reached) then write that full 8MB to the network all at once. This behavior does not play nicely with --limit-upload, which only limits the Reader passed to Media. While the long-term average upload rate will be correctly limited, the actual network bandwidth will be very spikey. e.g., if an 8MB/s connection is limited to 1MB/s, Media().Do() will spend 8s reading from the rate-limited reader (performing no network requests), then 1s writing to the network at 8MB/s. This is bad for network connections hurt by full-speed uploads, particularly when writing 8MB will take several seconds. Disable resumable uploads entirely by setting the chunk size to zero. This causes the io.Reader to be passed further down the request stack, where there is less (but still some) buffering. My connection is around 1.5MB/s up, with nominal ~15ms ping times to 8.8.8.8. Without this change, --limit-upload 1024 results in several seconds of ~200ms ping times (uploading), followed by several seconds of ~15ms ping times (reading from rate-limited reader). A bandwidth monitor reports this as several seconds of ~1.5MB/s followed by several seconds of 0.0MB/s. With this change, --limit-upload 1024 results in ~20ms ping times and the bandwidth monitor reports a constant ~1MB/s. I've elected to make this change unconditional of --limit-upload because the resumable uploads shouldn't be providing much benefit anyways, as restic already uploads mostly small blobs and already has a retry mechanism. --limit-download is not affected by this problem, as Get().Download() returns the real http.Response.Body without any internal buffering. Updates #1216 |
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