rclone/fs/chunksize/chunksize.go

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// Package chunksize calculates a suitable chunk size for large uploads
package chunksize
import (
"github.com/rclone/rclone/fs"
)
// Calculator calculates the minimum chunk size needed to fit within
// the maximum number of parts, rounded up to the nearest fs.Mebi.
//
// For most backends, (chunk_size) * (concurrent_upload_routines)
// memory will be required so we want to use the smallest possible
// chunk size that's going to allow the upload to proceed. Rounding up
// to the nearest fs.Mebi on the assumption that some backends may
// only allow integer type parameters when specifying the chunk size.
//
// Returns the default chunk size if it is sufficiently large enough
// to support the given file size otherwise returns the smallest chunk
// size necessary to allow the upload to proceed.
func Calculator(o interface{}, size int64, maxParts int, defaultChunkSize fs.SizeSuffix) fs.SizeSuffix {
// If streaming then use default chunk size
if size < 0 {
fs.Debugf(o, "Streaming upload with chunk_size %s allows uploads of up to %s and will fail only when that limit is reached.", defaultChunkSize, fs.SizeSuffix(maxParts)*defaultChunkSize)
return defaultChunkSize
}
fileSize := fs.SizeSuffix(size)
requiredChunks := fileSize / defaultChunkSize
if requiredChunks < fs.SizeSuffix(maxParts) || (requiredChunks == fs.SizeSuffix(maxParts) && fileSize%defaultChunkSize == 0) {
return defaultChunkSize
}
minChunk := fileSize / fs.SizeSuffix(maxParts)
remainder := minChunk % fs.Mebi
if remainder != 0 {
minChunk += fs.Mebi - remainder
}
if fileSize/minChunk == fs.SizeSuffix(maxParts) && fileSize%fs.SizeSuffix(maxParts) != 0 { // when right on the boundary, we need to add a MiB
minChunk += fs.Mebi
}
fs.Debugf(o, "size: %v, parts: %v, default: %v, new: %v; default chunk size insufficient, returned new chunk size", fileSize, maxParts, defaultChunkSize, minChunk)
return minChunk
}