ceremonyclient/pebble/internal/keyspan/truncate.go

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2024-01-03 07:31:42 +00:00
// Copyright 2019 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"
// Truncate creates a new iterator where every span in the supplied iterator is
// truncated to be contained within the range [lower, upper). If start and end
// are specified, filter out any spans that are completely outside those bounds.
func Truncate(
cmp base.Compare,
iter FragmentIterator,
lower, upper []byte,
start, end *base.InternalKey,
panicOnUpperTruncate bool,
) FragmentIterator {
return Filter(iter, func(in *Span, out *Span) (keep bool) {
out.Start, out.End = in.Start, in.End
out.Keys = append(out.Keys[:0], in.Keys...)
// Ignore this span if it lies completely outside start, end. Note that
// end endInclusive indicated whether end is inclusive.
//
// The comparison between s.End and start is by user key only, as
// the span is exclusive at s.End, so comparing by user keys
// is sufficient.
if start != nil && cmp(in.End, start.UserKey) <= 0 {
return false
}
if end != nil {
v := cmp(in.Start, end.UserKey)
switch {
case v > 0:
// Wholly outside the end bound. Skip it.
return false
case v == 0:
// This span begins at the same user key as `end`. Whether or
// not any of the keys contained within the span are relevant is
// dependent on Trailers. Any keys contained within the span
// with trailers larger than end cover the small sliver of
// keyspace between [k#inf, k#<end-seqnum>]. Since keys are
// sorted descending by Trailer within the span, we need to find
// the prefix of keys with larger trailers.
for i := range in.Keys {
if in.Keys[i].Trailer < end.Trailer {
out.Keys = out.Keys[:i]
break
}
}
default:
// Wholly within the end bound. Keep it.
}
}
var truncated bool
// Truncate the bounds to lower and upper.
if cmp(in.Start, lower) < 0 {
out.Start = lower
}
if cmp(in.End, upper) > 0 {
truncated = true
out.End = upper
}
if panicOnUpperTruncate && truncated {
panic("pebble: upper bound should not be truncated")
}
return !out.Empty() && cmp(out.Start, out.End) < 0
}, cmp)
}