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block_stream_merger.go
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/
block_stream_merger.go
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package storage
import (
"container/heap"
"fmt"
"io"
)
// blockStreamMerger is used for merging block streams.
type blockStreamMerger struct {
// The current block to work with.
Block *Block
bsrHeap blockStreamReaderHeap
// Whether the call to NextBlock must be no-op.
nextBlockNoop bool
// The last error
err error
}
func (bsm *blockStreamMerger) reset() {
bsm.Block = nil
for i := range bsm.bsrHeap {
bsm.bsrHeap[i] = nil
}
bsm.bsrHeap = bsm.bsrHeap[:0]
bsm.nextBlockNoop = false
bsm.err = nil
}
// Init initializes bsm with the given bsrs.
func (bsm *blockStreamMerger) Init(bsrs []*blockStreamReader) {
bsm.reset()
for _, bsr := range bsrs {
if bsr.NextBlock() {
bsm.bsrHeap = append(bsm.bsrHeap, bsr)
continue
}
if err := bsr.Error(); err != nil {
bsm.err = fmt.Errorf("cannot obtain the next block to merge: %s", err)
return
}
}
if len(bsm.bsrHeap) == 0 {
bsm.err = io.EOF
return
}
heap.Init(&bsm.bsrHeap)
bsm.Block = &bsm.bsrHeap[0].Block
bsm.nextBlockNoop = true
}
// NextBlock stores the next block in bsm.Block.
//
// The blocks are sorted by (TDIS, MinTimestamp). Two subsequent blocks
// for the same TSID may contain overlapped time ranges.
func (bsm *blockStreamMerger) NextBlock() bool {
if bsm.err != nil {
return false
}
if bsm.nextBlockNoop {
bsm.nextBlockNoop = false
return true
}
bsm.err = bsm.nextBlock()
switch bsm.err {
case nil:
return true
case io.EOF:
return false
default:
bsm.err = fmt.Errorf("cannot obtain the next block to merge: %s", bsm.err)
return false
}
}
func (bsm *blockStreamMerger) nextBlock() error {
bsrMin := bsm.bsrHeap[0]
if bsrMin.NextBlock() {
heap.Fix(&bsm.bsrHeap, 0)
bsm.Block = &bsm.bsrHeap[0].Block
return nil
}
if err := bsrMin.Error(); err != nil {
return err
}
heap.Pop(&bsm.bsrHeap)
if len(bsm.bsrHeap) == 0 {
return io.EOF
}
bsm.Block = &bsm.bsrHeap[0].Block
return nil
}
func (bsm *blockStreamMerger) Error() error {
if bsm.err == io.EOF {
return nil
}
return bsm.err
}
type blockStreamReaderHeap []*blockStreamReader
func (bsrh *blockStreamReaderHeap) Len() int {
return len(*bsrh)
}
func (bsrh *blockStreamReaderHeap) Less(i, j int) bool {
x := *bsrh
a, b := &x[i].Block.bh, &x[j].Block.bh
if a.TSID.MetricID == b.TSID.MetricID {
// Fast path for identical TSID values.
return a.MinTimestamp < b.MinTimestamp
}
// Slow path for distinct TSID values.
return a.TSID.Less(&b.TSID)
}
func (bsrh *blockStreamReaderHeap) Swap(i, j int) {
x := *bsrh
x[i], x[j] = x[j], x[i]
}
func (bsrh *blockStreamReaderHeap) Push(x interface{}) {
*bsrh = append(*bsrh, x.(*blockStreamReader))
}
func (bsrh *blockStreamReaderHeap) Pop() interface{} {
a := *bsrh
v := a[len(a)-1]
*bsrh = a[:len(a)-1]
return v
}