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Return an empty iterator when no chunks are present #1355

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Return an empty iterator when no chunks are present #1355

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13 changes: 13 additions & 0 deletions pkg/chunk/encoding/bigchunk.go
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,10 @@ func (b *bigchunk) Size() int {
}

func (b *bigchunk) NewIterator() Iterator {
if len(b.chunks) == 0 {
return emptyIterator{}
}

return &bigchunkIterator{
bigchunk: b,
curr: b.chunks[0].Iterator(),
Expand Down Expand Up @@ -332,3 +336,12 @@ func firstAndLastTimes(c chunkenc.Chunk) (int64, int64, error) {
}
return first, last, iter.Err()
}

// emptyIterator has no samples.
type emptyIterator struct{}
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@bboreham bboreham Apr 30, 2019

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How about using NewNopIterator() from TSDB instead of this?
AFAICS only Batch() would behave differently, and that might indicate a bug.

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@gouthamve gouthamve May 6, 2019

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NewNopIterator() returns a tsdb.Iterator as seen here: https://github.com/prometheus/tsdb/blob/719b57db44f5e5dbad7d813a5645c222c3ba7647/chunkenc/chunk.go#L55-L65

Not sure how it'll be simpler to use that than just add a few lines here.

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@bboreham bboreham May 6, 2019

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because then you won't add any lines here?

I'm pretty sure it returns a chunkenc.Iterator, i.e. it fits in curr.

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@bboreham bboreham Jun 11, 2019

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I created #1461 to make clear what I meant.


func (emptyIterator) Scan() bool { return false }
func (emptyIterator) FindAtOrAfter(model.Time) bool { return false }
func (emptyIterator) Value() model.SamplePair { return model.SamplePair{} }
func (emptyIterator) Batch(size int) Batch { return Batch{} }
func (emptyIterator) Err() error { return nil }