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			49 lines
		
	
	
		
			1.7 KiB
		
	
	
	
		
			Go
		
	
	
	
	
	
			
		
		
	
	
			49 lines
		
	
	
		
			1.7 KiB
		
	
	
	
		
			Go
		
	
	
	
	
	
// Copyright 2018 The LevelDB-Go and Pebble Authors. All rights reserved. Use
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// of this source code is governed by a BSD-style license that can be found in
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// the LICENSE file.
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package keyspan
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import "github.com/cockroachdb/pebble/internal/base"
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// SeekLE seeks to the span that contains or is before the target key.
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func SeekLE(cmp base.Compare, iter FragmentIterator, key []byte) *Span {
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	// NB: We use SeekLT in order to land on the proper span for a search
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	// key that resides in the middle of a span. Consider the scenario:
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	//
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	//     a---e
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	//         e---i
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	//
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	// The spans are indexed by their start keys `a` and `e`. If the
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	// search key is `c` we want to land on the span [a,e). If we were to
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	// use SeekGE then the search key `c` would land on the span [e,i) and
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	// we'd have to backtrack. The one complexity here is what happens for the
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	// search key `e`. In that case SeekLT will land us on the span [a,e)
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	// and we'll have to move forward.
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	iterSpan := iter.SeekLT(key)
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	if iterSpan == nil {
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		// Advance the iterator once to see if the next span has a start key
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		// equal to key.
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		iterSpan = iter.Next()
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		if iterSpan == nil || cmp(key, iterSpan.Start) < 0 {
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			// The iterator is exhausted or we've hit the next span.
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			return nil
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		}
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	} else {
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		// Invariant: key > iterSpan.Start
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		if cmp(key, iterSpan.End) >= 0 {
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			// The current span lies entirely before the search key. Check to see if
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			// the next span contains the search key. If it doesn't, we'll backup
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			// and return to our earlier candidate.
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			iterSpan = iter.Next()
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			if iterSpan == nil || cmp(key, iterSpan.Start) < 0 {
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				// The next span is past our search key or there is no next span. Go
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				// back.
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				iterSpan = iter.Prev()
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			}
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		}
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	}
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	return iterSpan
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}
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