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tart push: use fixed size chunks to allow for better deduplication #821

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May 14, 2024
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tart push: use fixed size chunks to allow for better deduplication #821

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56 changes: 6 additions & 50 deletions Sources/tart/OCI/Layerizer/DiskV2.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -13,25 +13,22 @@ class DiskV2: Disk {
let mappedDisk = try Data(contentsOf: diskURL, options: [.alwaysMapped])

// Compress the disk file as multiple individually decompressible streams,
// each equal ``Self.layerLimitBytes`` bytes or slightly larger due to the
// internal compressor's buffer
var offset: UInt64 = 0

while let (compressedData, uncompressedSize, uncompressedDigest) = try compressNextLayerOfLimitBytesOrMore(mappedDisk: mappedDisk, offset: offset) {
offset += uncompressedSize
// each equal ``Self.layerLimitBytes`` bytes or less due to LZ4 compression
for data in mappedDisk.chunks(ofCount: layerLimitBytes) {
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Should we put layerLimitBytes in the manifest in case it's gonna change at some point?

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@edigaryev edigaryev May 14, 2024 •
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I think it's already there by the virtue of passing the UInt64(data.count) as uncompressedSize argument to OCIManifestLayer(...):

tart/Sources/tart/OCI/Manifest.swift

Lines 94 to 96 in 13d5ddb

if let uncompressedSize = uncompressedSize {
annotations[uncompressedSizeAnnotation] = String(uncompressedSize)
}

let compressedData = try (data as NSData).compressed(using: .lz4) as Data

let layerDigest = try await registry.pushBlob(fromData: compressedData, chunkSizeMb: chunkSizeMb)

pushedLayers.append(OCIManifestLayer(
mediaType: diskV2MediaType,
size: compressedData.count,
digest: layerDigest,
uncompressedSize: uncompressedSize,
uncompressedContentDigest: uncompressedDigest
uncompressedSize: UInt64(data.count),
uncompressedContentDigest: Digest.hash(data)
))

// Update progress using a relative value
progress.completedUnitCount += Int64(uncompressedSize)
progress.completedUnitCount += Int64(data.count)
}

return pushedLayers
Expand Down Expand Up @@ -144,45 +141,4 @@ class DiskV2: Disk {
}
}
}

private static func compressNextLayerOfLimitBytesOrMore(mappedDisk: Data, offset: UInt64) throws -> (Data, UInt64, String)? {
var compressedData = Data()
var bytesRead: UInt64 = 0
let digest = Digest()

// Create a compressing filter that we will terminate upon
// reaching ``Self.layerLimitBytes`` of compressed data
let compressingFilter = try InputFilter(.compress, using: .lz4, bufferCapacity: bufferSizeBytes) { (length: Int) -> Data? in
if compressedData.count >= Self.layerLimitBytes {
return nil
}

let readFromByte = Int(offset + bytesRead)

let numBytesToRead = min(mappedDisk.count - readFromByte, bufferSizeBytes)
if numBytesToRead == 0 {
return nil
}

let uncompressedChunk = mappedDisk.subdata(in: readFromByte ..< (readFromByte + numBytesToRead))

bytesRead += UInt64(uncompressedChunk.count)
digest.update(uncompressedChunk)

return uncompressedChunk
}

// Retrieve compressed data chunks, but normally no more than ``Self.layerLimitBytes`` bytes
while let compressedChunk = try compressingFilter.readData(ofLength: Self.bufferSizeBytes) {
compressedData.append(compressedChunk)
}

// Nothing was read this time from the disk,
// signal that to the consumer
if bytesRead == 0 {
return nil
}

return (compressedData, bytesRead, digest.finalize())
}
}
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