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