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XL/erasure-read: read disks in parallel. (#1975)

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On read failure, fallback to reads from other
disks also happen in parallel.
This commit is contained in:
Krishna Srinivas 2016-06-24 18:00:34 -07:00 committed by Harshavardhana
parent a3a310cde8
commit cb1200a66d
1 changed files with 153 additions and 151 deletions
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304
erasure-readfile.go
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@ -26,42 +26,42 @@ import (
"github.com/klauspost/reedsolomon"
)
// isSuccessDecodeBlocks - do we have all the blocks to be successfully decoded?.
// input disks here are expected to be ordered i.e parityBlocks
// are preceded by dataBlocks. For for information look at getOrderedDisks().
func isSuccessDecodeBlocks(disks []StorageAPI, dataBlocks int) bool {
// isSuccessDecodeBlocks - do we have all the blocks to be
// successfully decoded?. Input encoded blocks ordered matrix.
func isSuccessDecodeBlocks(enBlocks [][]byte, dataBlocks int) bool {
// Count number of data and parity blocks that were read.
var successDataBlocksCount = 0
var successParityBlocksCount = 0
for index, disk := range disks {
if disk == nil {
for index := range enBlocks {
if enBlocks[index] == nil {
continue
}
// block index lesser than data blocks, update data block count.
if index < dataBlocks {
successDataBlocksCount++
continue
}
} // else { // update parity block count.
successParityBlocksCount++
}
// Returns true if we have atleast dataBlocks + 1 parity.
return successDataBlocksCount+successParityBlocksCount >= dataBlocks+1
return successDataBlocksCount == dataBlocks || successDataBlocksCount+successParityBlocksCount >= dataBlocks+1
}
// isSuccessDataBlocks - do we have all the data blocks?
// input disks here are expected to be ordered i.e parityBlocks
// are preceded by dataBlocks. For for information look at getOrderedDisks().
func isSuccessDataBlocks(disks []StorageAPI, dataBlocks int) bool {
// Input encoded blocks ordered matrix.
func isSuccessDataBlocks(enBlocks [][]byte, dataBlocks int) bool {
// Count number of data blocks that were read.
var successDataBlocksCount = 0
for index, disk := range disks[:dataBlocks] {
if disk == nil {
for index := range enBlocks[:dataBlocks] {
if enBlocks[index] == nil {
continue
}
// block index lesser than data blocks, update data block count.
if index < dataBlocks {
successDataBlocksCount++
}
}
// Returns true if we have all the dataBlocks.
// Returns true if we have atleast the dataBlocks.
return successDataBlocksCount >= dataBlocks
}
@ -79,6 +79,52 @@ func getOrderedDisks(distribution []int, disks []StorageAPI, blockCheckSums []ch
return orderedDisks, orderedBlockCheckSums
}
// Return readable disks slice from which we can read parallely.
func getReadDisks(orderedDisks []StorageAPI, index int, dataBlocks int) (readDisks []StorageAPI, nextIndex int, err error) {
readDisks = make([]StorageAPI, len(orderedDisks))
dataDisks := 0
parityDisks := 0
// Count already read data and parity chunks.
for i := 0; i < index; i++ {
if orderedDisks[i] == nil {
continue
}
if i < dataBlocks {
dataDisks++
} else {
parityDisks++
}
}
// Sanity checks - we should never have this situation.
if dataDisks == dataBlocks {
return nil, 0, errUnexpected
}
if dataDisks+parityDisks >= dataBlocks+1 {
return nil, 0, errUnexpected
}
// Find the disks from which next set of parallel reads should happen.
for i := index; i < len(orderedDisks); i++ {
if orderedDisks[i] == nil {
continue
}
if i < dataBlocks {
dataDisks++
} else {
parityDisks++
}
readDisks[i] = orderedDisks[i]
if dataDisks == dataBlocks {
return readDisks, i + 1, nil
}
if dataDisks+parityDisks == dataBlocks+1 {
return readDisks, i + 1, nil
}
}
return nil, 0, errXLReadQuorum
}
// erasureReadFile - read bytes from erasure coded files and writes to given writer.
// Erasure coded files are read block by block as per given erasureInfo and data chunks
// are decoded into a data block. Data block is trimmed for given offset and length,
@ -95,9 +141,9 @@ func erasureReadFile(writer io.Writer, disks []StorageAPI, volume string, path s
// disks and rest will be parity.
orderedDisks, orderedBlockCheckSums := getOrderedDisks(eInfo.Distribution, disks, blockCheckSums)
// bitrotVerify verifies if the file on a particular disk doesn't have bitrot
// bitRotVerify verifies if the file on a particular disk doesn't have bitrot
// by verifying the hash of the contents of the file.
bitrotVerify := func() func(diskIndex int) bool {
bitRotVerify := func() func(diskIndex int) bool {
verified := make([]bool, len(orderedDisks))
// Return closure so that we have reference to []verified and
// not recalculate the hash on it everytime the function is
@ -117,9 +163,6 @@ func erasureReadFile(writer io.Writer, disks []StorageAPI, volume string, path s
// Total bytes written to writer
bytesWritten := int64(0)
// Each element of enBlocks holds curChunkSize'd amount of data read from its corresponding disk.
enBlocks := make([][]byte, len(orderedDisks))
// chunkSize is roughly BlockSize/DataBlocks.
// chunkSize is calculated such that chunkSize*DataBlocks accommodates BlockSize bytes.
// So chunkSize*DataBlocks can be slightly larger than BlockSize if BlockSize is not divisible by
@ -133,11 +176,23 @@ func erasureReadFile(writer io.Writer, disks []StorageAPI, volume string, path s
// need to read parity disks. If one of the data disk is missing we need to read DataBlocks+1 number
// of disks. Once read, we Reconstruct() missing data if needed and write it to the given writer.
for block := startBlock; bytesWritten < length; block++ {
// Each element of enBlocks holds curChunkSize'd amount of data read from its corresponding disk.
enBlocks := make([][]byte, len(orderedDisks))
// enBlocks data can have 0-padding hence we need to figure the exact number
// of bytes we want to read from enBlocks.
blockSize := eInfo.BlockSize
// curChunkSize is chunkSize until end block.
curChunkSize := chunkSize
// We have endBlock, verify if we need to have padding.
if block == endBlock && (totalLength%eInfo.BlockSize != 0) {
// If this is the last block and size of the block is < BlockSize.
curChunkSize = getEncodedBlockLen(totalLength%eInfo.BlockSize, eInfo.DataBlocks)
// For the last block, the block size can be less than BlockSize.
blockSize = totalLength % eInfo.BlockSize
}
// Block offset.
@ -146,148 +201,95 @@ func erasureReadFile(writer io.Writer, disks []StorageAPI, volume string, path s
// then it can result in wrong offset for the last block.
blockOffset := block * chunkSize
// Figure out the number of disks that are needed for the read.
// We will need DataBlocks number of disks if all the data disks are up.
// We will need DataBlocks+1 number of disks even if one of the data disks is down.
readableDiskCount := 0
// nextIndex - index from which next set of parallel reads
// should happen.
nextIndex := 0
// Count the number of data disks that are up.
for _, disk := range orderedDisks[:eInfo.DataBlocks] {
if disk == nil {
continue
// parallelRead() reads DataBlocks number of disks if all data
// disks are available or DataBlocks+1 number of disks if one
// of the data disks is missing. All the reads happen in parallel.
var parallelRead func() error
parallelRead = func() error {
// If enough blocks are available to do rs.Reconstruct()
if isSuccessDecodeBlocks(enBlocks, eInfo.DataBlocks) {
return nil
}
readableDiskCount++
}
// Readable disks..
if readableDiskCount < eInfo.DataBlocks {
// Not enough data disks up, so we need DataBlocks+1 number
// of disks for reed-solomon Reconstruct()
readableDiskCount = eInfo.DataBlocks + 1
}
// Initialize wait group.
var wg = &sync.WaitGroup{}
// Current disk index from which to read, this will be used later
// in case one of the parallel reads fails.
index := 0
// Read from the disks in parallel.
for _, disk := range orderedDisks {
if disk == nil {
index++
continue
if nextIndex == len(orderedDisks) {
// No more disks to read from.
return errXLReadQuorum
}
// Increment wait group.
wg.Add(1)
// Start reading from disk in a go-routine.
go func(index int, disk StorageAPI) {
defer wg.Done()
// Verify bit rot for this disk slice.
if !bitrotVerify(index) {
// So that we don't read from this disk for the next block.
orderedDisks[index] = nil
return
}
// Chunk writer.
chunkWriter := bytes.NewBuffer(make([]byte, 0, curChunkSize))
// CopyN copies until current chunk size.
err := copyN(chunkWriter, disk, volume, path, blockOffset, curChunkSize)
if err != nil {
// So that we don't read from this disk for the next block.
orderedDisks[index] = nil
return
}
// Copy the read blocks.
enBlocks[index] = chunkWriter.Bytes()
// Reset the buffer.
chunkWriter.Reset()
// Successfully read.
}(index, disk)
index++
readableDiskCount--
// We have read all the readable disks.
if readableDiskCount == 0 {
break
}
}
// Wait for all the reads to finish.
wg.Wait()
// FIXME: make this parallel.
// If we have all the data blocks no need to decode.
if !isSuccessDataBlocks(orderedDisks, eInfo.DataBlocks) {
// If we don't have DataBlocks number of data blocks we
// will have to read enough parity blocks such that we
// have DataBlocks+1 number for blocks for rs.Reconstruct().
// index is either dataBlocks or dataBlocks + 1.
for ; index < len(orderedDisks); index++ {
// We have enough blocks to decode, break out.
if isSuccessDecodeBlocks(orderedDisks, eInfo.DataBlocks) {
// We have DataBlocks+1 blocks, enough for rs.Reconstruct()
break
}
// This disk was previously set to nil and ignored, do not read again.
if orderedDisks[index] == nil {
continue
}
// Verify bit-rot for this index.
if !bitrotVerify(index) {
// Mark nil so that we don't read from this disk for the next block.
orderedDisks[index] = nil
continue
}
// Chunk writer.
chunkWriter := bytes.NewBuffer(make([]byte, 0, curChunkSize))
// CopyN copies until current chunk size.
err := copyN(chunkWriter, orderedDisks[index], volume, path, blockOffset, curChunkSize)
if err != nil {
// ERROR: Mark nil so that we don't read from
// this disk for the next block.
orderedDisks[index] = nil
continue
}
// Copy the read blocks.
chunkWriter.Read(enBlocks[index])
// Reset the buffer.
chunkWriter.Reset()
}
// Reconstruct the missing data blocks.
err := decodeData(enBlocks, eInfo.DataBlocks, eInfo.ParityBlocks)
// readDisks - disks from which we need to read in parallel.
var readDisks []StorageAPI
var err error
readDisks, nextIndex, err = getReadDisks(orderedDisks, nextIndex, eInfo.DataBlocks)
if err != nil {
return err
}
// WaitGroup to synchronise the read go-routines.
wg := &sync.WaitGroup{}
// Read disks in parallel.
for index := range readDisks {
if readDisks[index] == nil {
continue
}
wg.Add(1)
// Reads chunk from readDisk[index] in routine.
go func(index int) {
defer wg.Done()
// Verify bit rot for the file on this disk.
if !bitRotVerify(index) {
// So that we don't read from this disk for the next block.
orderedDisks[index] = nil
return
}
// Chunk writer.
chunkWriter := bytes.NewBuffer(make([]byte, 0, curChunkSize))
// CopyN - copies until current chunk size.
err := copyN(chunkWriter, readDisks[index], volume, path, blockOffset, curChunkSize)
if err != nil {
// So that we don't read from this disk for the next block.
orderedDisks[index] = nil
return
}
// Copy the read blocks.
enBlocks[index] = chunkWriter.Bytes()
// Reset the buffer.
chunkWriter.Reset()
// Successfully read.
}(index)
}
// Waiting for first routines to finish.
wg.Wait()
// Continue to read the rest of the blocks in parallel.
return parallelRead()
}
// Start reading all blocks in parallel.
err := parallelRead()
if err != nil {
return bytesWritten, err
}
// If we have all the data blocks no need to decode, continue to write.
if !isSuccessDataBlocks(enBlocks, eInfo.DataBlocks) {
// Reconstruct the missing data blocks.
if err = decodeData(enBlocks, eInfo.DataBlocks, eInfo.ParityBlocks); err != nil {
return bytesWritten, err
}
// Success.
}
var outSize, outOffset int64
// enBlocks data can have 0-padding hence we need to figure the exact number
// of bytes we want to read from enBlocks.
blockSize := eInfo.BlockSize
if block == endBlock && totalLength%eInfo.BlockSize != 0 {
// For the last block, the block size can be less than BlockSize.
blockSize = totalLength % eInfo.BlockSize
}
// If this is start block, skip unwanted bytes.
if block == startBlock {
outOffset = bytesToSkip