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87 lines
2.7 KiB
87 lines
2.7 KiB
package erasure_coding
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import (
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"github.com/chrislusf/seaweedfs/weed/storage/types"
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)
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type Interval struct {
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BlockIndex int
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InnerBlockOffset int64
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Size types.Size
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IsLargeBlock bool
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LargeBlockRowsCount int
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}
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func LocateData(largeBlockLength, smallBlockLength int64, datSize int64, offset int64, size types.Size) (intervals []Interval) {
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blockIndex, isLargeBlock, innerBlockOffset := locateOffset(largeBlockLength, smallBlockLength, datSize, offset)
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// adding DataShardsCount*smallBlockLength to ensure we can derive the number of large block size from a shard size
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nLargeBlockRows := int((datSize + DataShardsCount*smallBlockLength) / (largeBlockLength * DataShardsCount))
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for size > 0 {
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interval := Interval{
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BlockIndex: blockIndex,
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InnerBlockOffset: innerBlockOffset,
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IsLargeBlock: isLargeBlock,
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LargeBlockRowsCount: nLargeBlockRows,
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}
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blockRemaining := largeBlockLength - innerBlockOffset
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if !isLargeBlock {
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blockRemaining = smallBlockLength - innerBlockOffset
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}
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if int64(size) <= blockRemaining {
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interval.Size = size
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intervals = append(intervals, interval)
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return
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}
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interval.Size = types.Size(blockRemaining)
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intervals = append(intervals, interval)
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size -= interval.Size
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blockIndex += 1
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if isLargeBlock && blockIndex == nLargeBlockRows*DataShardsCount {
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isLargeBlock = false
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blockIndex = 0
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}
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innerBlockOffset = 0
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}
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return
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}
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func locateOffset(largeBlockLength, smallBlockLength int64, datSize int64, offset int64) (blockIndex int, isLargeBlock bool, innerBlockOffset int64) {
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largeRowSize := largeBlockLength * DataShardsCount
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nLargeBlockRows := datSize / (largeBlockLength * DataShardsCount)
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// if offset is within the large block area
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if offset < nLargeBlockRows*largeRowSize {
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isLargeBlock = true
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blockIndex, innerBlockOffset = locateOffsetWithinBlocks(largeBlockLength, offset)
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return
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}
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isLargeBlock = false
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offset -= nLargeBlockRows * largeRowSize
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blockIndex, innerBlockOffset = locateOffsetWithinBlocks(smallBlockLength, offset)
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return
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}
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func locateOffsetWithinBlocks(blockLength int64, offset int64) (blockIndex int, innerBlockOffset int64) {
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blockIndex = int(offset / blockLength)
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innerBlockOffset = offset % blockLength
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return
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}
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func (interval Interval) ToShardIdAndOffset(largeBlockSize, smallBlockSize int64) (ShardId, int64) {
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ecFileOffset := interval.InnerBlockOffset
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rowIndex := interval.BlockIndex / DataShardsCount
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if interval.IsLargeBlock {
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ecFileOffset += int64(rowIndex) * largeBlockSize
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} else {
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ecFileOffset += int64(interval.LargeBlockRowsCount)*largeBlockSize + int64(rowIndex)*smallBlockSize
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}
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ecFileIndex := interval.BlockIndex % DataShardsCount
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return ShardId(ecFileIndex), ecFileOffset
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}
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