erasure: read only dataBlocks if we have enough. (#1776)

Reconstruct with parity blocks if we don't have enough data blocks.
master
Harshavardhana 9 years ago committed by Harshavardhana
parent 302ec27fa2
commit 27cc8a6529
  1. 79
      erasure-readfile.go

@ -44,11 +44,12 @@ func (e erasure) ReadFile(volume, path string, startOffset int64, totalSize int6
go func(index int, disk StorageAPI) {
defer rwg.Done()
offset := int64(0)
if reader, err := disk.ReadFile(volume, path, offset); err == nil {
reader, err := disk.ReadFile(volume, path, offset)
if err == nil {
readers[index] = reader
} else {
errs[index] = err
return
}
errs[index] = err
}(index, disk)
}
@ -69,61 +70,73 @@ func (e erasure) ReadFile(volume, path string, startOffset int64, totalSize int6
var totalLeft = totalSize
// Read until EOF.
for totalLeft > 0 {
// Figure out the right blockSize as it was encoded
// before.
// Figure out the right blockSize as it was encoded before.
var curBlockSize int64
if erasureBlockSize < totalLeft {
curBlockSize = erasureBlockSize
} else {
curBlockSize = totalLeft
}
// Calculate the current encoded block size.
curEncBlockSize := getEncodedBlockLen(curBlockSize, e.DataBlocks)
// Allocate encoded blocks up to storage disks.
enBlocks := make([][]byte, len(e.storageDisks))
// Counter to keep success data blocks.
var successDataBlocksCount = 0
var noReconstruct bool // Set for no reconstruction.
// Read all the readers.
for index, reader := range readers {
blockIndex := e.distribution[index] - 1
// Initialize shard slice and fill the data from each parts.
enBlocks[blockIndex] = make([]byte, curEncBlockSize)
if reader == nil {
enBlocks[blockIndex] = nil
continue
}
// Close the reader when routine returns.
defer reader.Close()
// Read the necessary blocks.
_, rErr := io.ReadFull(reader, enBlocks[blockIndex])
if rErr != nil && rErr != io.ErrUnexpectedEOF {
readers[index].Close()
readers[index] = nil
enBlocks[blockIndex] = nil
}
// Verify if we have successfully all the data blocks.
if blockIndex < e.DataBlocks {
successDataBlocksCount++
// Set when we have all the data blocks and no
// reconstruction is needed, so that we can avoid
// erasure reconstruction.
noReconstruct = successDataBlocksCount == e.DataBlocks
if noReconstruct {
// Break out we have read all the data blocks.
break
}
}
}
// Check blocks if they are all zero in length.
// Check blocks if they are all zero in length, we have
// corruption return error.
if checkBlockSize(enBlocks) == 0 {
pipeWriter.CloseWithError(errDataCorrupt)
return
}
// Verify the blocks.
ok, err := e.ReedSolomon.Verify(enBlocks)
if err != nil {
pipeWriter.CloseWithError(err)
return
}
// Verification failed, blocks require reconstruction.
if !ok {
for index, reader := range readers {
if reader == nil {
// Reconstruct expects missing blocks to be nil.
enBlocks[index] = nil
}
}
err = e.ReedSolomon.Reconstruct(enBlocks)
// Verify if reconstruction is needed, proceed with reconstruction.
if !noReconstruct {
err := e.ReedSolomon.Reconstruct(enBlocks)
if err != nil {
pipeWriter.CloseWithError(err)
return
}
// Verify reconstructed blocks again.
ok, err = e.ReedSolomon.Verify(enBlocks)
// Verify reconstructed blocks (parity).
ok, err := e.ReedSolomon.Verify(enBlocks)
if err != nil {
pipeWriter.CloseWithError(err)
return
@ -136,7 +149,7 @@ func (e erasure) ReadFile(volume, path string, startOffset int64, totalSize int6
}
}
// Get all the data blocks.
// Get data blocks from encoded blocks.
dataBlocks := getDataBlocks(enBlocks, e.DataBlocks, int(curBlockSize))
// Verify if the offset is right for the block, if not move to the next block.
@ -151,8 +164,8 @@ func (e erasure) ReadFile(volume, path string, startOffset int64, totalSize int6
startOffset = startOffset + int64(len(dataBlocks))
}
// Write safely the necessary blocks.
_, err = pipeWriter.Write(dataBlocks[int(startOffset):])
// Write safely the necessary blocks to the pipe.
_, err := pipeWriter.Write(dataBlocks[int(startOffset):])
if err != nil {
pipeWriter.CloseWithError(err)
return
@ -170,14 +183,6 @@ func (e erasure) ReadFile(volume, path string, startOffset int64, totalSize int6
// Cleanly end the pipe after a successful decoding.
pipeWriter.Close()
// Cleanly close all the underlying data readers.
for _, reader := range readers {
if reader == nil {
continue
}
reader.Close()
}
}()
// Return the pipe for the top level caller to start reading.

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