mirror of
https://source.quilibrium.com/quilibrium/ceremonyclient.git
synced 2024-11-11 02:35:18 +00:00
269 lines
8.9 KiB
Go
269 lines
8.9 KiB
Go
// Copyright 2022 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"
|
|
|
|
// TODO(jackson): Consider removing this type and adding bounds enforcement
|
|
// directly to the MergingIter. This type is probably too lightweight to warrant
|
|
// its own type, but for now we implement it separately for expediency.
|
|
|
|
// boundedIterPos records the position of the BoundedIter relative to the
|
|
// underlying iterator's position. It's used to avoid Next/Prev-ing the iterator
|
|
// if there can't possibly be another span within bounds, because the current
|
|
// span overlaps the bound.
|
|
//
|
|
// Imagine bounds [a,c) and an iterator that seeks to a span [b,d). The span
|
|
// [b,d) overlaps some portion of the iterator bounds, so the iterator must
|
|
// return it. If the iterator is subsequently Nexted, Next can tell that the
|
|
// iterator is exhausted without advancing the underlying iterator because the
|
|
// current span's end bound of d is ≥ the upper bound of c. In this case, the
|
|
// bounded iterator returns nil and records i.pos as posAtUpperLimit to remember
|
|
// that the underlying iterator position does not match the current BoundedIter
|
|
// position.
|
|
type boundedIterPos int8
|
|
|
|
const (
|
|
posAtLowerLimit boundedIterPos = -1
|
|
posAtIterSpan boundedIterPos = 0
|
|
posAtUpperLimit boundedIterPos = +1
|
|
)
|
|
|
|
// BoundedIter implements FragmentIterator and enforces bounds.
|
|
//
|
|
// Like the point InternalIterator interface, the bounded iterator's forward
|
|
// positioning routines (SeekGE, First, and Next) only check the upper bound.
|
|
// The reverse positioning routines (SeekLT, Last, and Prev) only check the
|
|
// lower bound. It is up to the caller to ensure that the forward positioning
|
|
// routines respect the lower bound and the reverse positioning routines respect
|
|
// the upper bound (i.e. calling SeekGE instead of First if there is a lower
|
|
// bound, and SeekLT instead of Last if there is an upper bound).
|
|
//
|
|
// When the hasPrefix parameter indicates that the iterator is in prefix
|
|
// iteration mode, BoundedIter elides any spans that do not overlap with the
|
|
// prefix's keyspace. In prefix iteration mode, reverse iteration is disallowed,
|
|
// except for an initial SeekLT with a seek key greater than or equal to the
|
|
// prefix. In prefix iteration mode, the first seek must position the iterator
|
|
// at or immediately before the first fragment covering a key greater than or
|
|
// equal to the prefix.
|
|
type BoundedIter struct {
|
|
iter FragmentIterator
|
|
iterSpan *Span
|
|
cmp base.Compare
|
|
split base.Split
|
|
lower []byte
|
|
upper []byte
|
|
hasPrefix *bool
|
|
prefix *[]byte
|
|
pos boundedIterPos
|
|
}
|
|
|
|
// Init initializes the bounded iterator.
|
|
//
|
|
// In addition to the iterator bounds, Init takes pointers to a boolean
|
|
// indicating whether the iterator is in prefix iteration mode and the prefix
|
|
// key if it is. This is used to exclude spans that are outside the iteration
|
|
// prefix.
|
|
//
|
|
// hasPrefix and prefix are allowed to be nil, however if hasPrefix != nil,
|
|
// prefix must also not be nil.
|
|
func (i *BoundedIter) Init(
|
|
cmp base.Compare,
|
|
split base.Split,
|
|
iter FragmentIterator,
|
|
lower, upper []byte,
|
|
hasPrefix *bool,
|
|
prefix *[]byte,
|
|
) {
|
|
*i = BoundedIter{
|
|
iter: iter,
|
|
cmp: cmp,
|
|
split: split,
|
|
lower: lower,
|
|
upper: upper,
|
|
hasPrefix: hasPrefix,
|
|
prefix: prefix,
|
|
}
|
|
}
|
|
|
|
var _ FragmentIterator = (*BoundedIter)(nil)
|
|
|
|
// Seek calls.
|
|
//
|
|
// Seek calls check iterator bounds in the direction of the seek. Additionally,
|
|
// if the iterator is in prefix iteration mode, seek calls check both start and
|
|
// end bounds against the prefix's bounds. We check both bounds for defense in
|
|
// depth. This optimization has been a source of various bugs due to various
|
|
// other prefix iteration optimizations that can result in seek keys that don't
|
|
// respect the prefix bounds.
|
|
|
|
// SeekGE implements FragmentIterator.
|
|
func (i *BoundedIter) SeekGE(key []byte) *Span {
|
|
s := i.iter.SeekGE(key)
|
|
s = i.checkPrefixSpanStart(s)
|
|
s = i.checkPrefixSpanEnd(s)
|
|
return i.checkForwardBound(s)
|
|
}
|
|
|
|
// SeekLT implements FragmentIterator.
|
|
func (i *BoundedIter) SeekLT(key []byte) *Span {
|
|
s := i.iter.SeekLT(key)
|
|
s = i.checkPrefixSpanStart(s)
|
|
s = i.checkPrefixSpanEnd(s)
|
|
return i.checkBackwardBound(s)
|
|
}
|
|
|
|
// First implements FragmentIterator.
|
|
func (i *BoundedIter) First() *Span {
|
|
s := i.iter.First()
|
|
s = i.checkPrefixSpanStart(s)
|
|
return i.checkForwardBound(s)
|
|
}
|
|
|
|
// Last implements FragmentIterator.
|
|
func (i *BoundedIter) Last() *Span {
|
|
s := i.iter.Last()
|
|
s = i.checkPrefixSpanEnd(s)
|
|
return i.checkBackwardBound(s)
|
|
}
|
|
|
|
// Next implements FragmentIterator.
|
|
func (i *BoundedIter) Next() *Span {
|
|
switch i.pos {
|
|
case posAtLowerLimit:
|
|
// The BoundedIter had previously returned nil, because it knew from
|
|
// i.iterSpan's bounds that there was no previous span. To Next, we only
|
|
// need to return the current iter span and reset i.pos to reflect that
|
|
// we're no longer positioned at the limit.
|
|
i.pos = posAtIterSpan
|
|
return i.iterSpan
|
|
case posAtIterSpan:
|
|
// If the span at the underlying iterator position extends to or beyond the
|
|
// upper bound, we can avoid advancing because the next span is necessarily
|
|
// out of bounds.
|
|
if i.iterSpan != nil && i.upper != nil && i.cmp(i.iterSpan.End, i.upper) >= 0 {
|
|
i.pos = posAtUpperLimit
|
|
return nil
|
|
}
|
|
// Similarly, if the span extends to the next prefix and we're in prefix
|
|
// iteration mode, we can avoid advancing.
|
|
if i.iterSpan != nil && i.hasPrefix != nil && *i.hasPrefix {
|
|
ei := i.split(i.iterSpan.End)
|
|
if i.cmp(i.iterSpan.End[:ei], *i.prefix) > 0 {
|
|
i.pos = posAtUpperLimit
|
|
return nil
|
|
}
|
|
}
|
|
return i.checkForwardBound(i.checkPrefixSpanStart(i.iter.Next()))
|
|
case posAtUpperLimit:
|
|
// Already exhausted.
|
|
return nil
|
|
default:
|
|
panic("unreachable")
|
|
}
|
|
}
|
|
|
|
// Prev implements FragmentIterator.
|
|
func (i *BoundedIter) Prev() *Span {
|
|
switch i.pos {
|
|
case posAtLowerLimit:
|
|
// Already exhausted.
|
|
return nil
|
|
case posAtIterSpan:
|
|
// If the span at the underlying iterator position extends to or beyond
|
|
// the lower bound, we can avoid advancing because the previous span is
|
|
// necessarily out of bounds.
|
|
if i.iterSpan != nil && i.lower != nil && i.cmp(i.iterSpan.Start, i.lower) <= 0 {
|
|
i.pos = posAtLowerLimit
|
|
return nil
|
|
}
|
|
// Similarly, if the span extends to or beyond the current prefix and
|
|
// we're in prefix iteration mode, we can avoid advancing.
|
|
if i.iterSpan != nil && i.hasPrefix != nil && *i.hasPrefix {
|
|
si := i.split(i.iterSpan.Start)
|
|
if i.cmp(i.iterSpan.Start[:si], *i.prefix) < 0 {
|
|
i.pos = posAtLowerLimit
|
|
return nil
|
|
}
|
|
}
|
|
return i.checkBackwardBound(i.checkPrefixSpanEnd(i.iter.Prev()))
|
|
case posAtUpperLimit:
|
|
// The BoundedIter had previously returned nil, because it knew from
|
|
// i.iterSpan's bounds that there was no next span. To Prev, we only
|
|
// need to return the current iter span and reset i.pos to reflect that
|
|
// we're no longer positioned at the limit.
|
|
i.pos = posAtIterSpan
|
|
return i.iterSpan
|
|
default:
|
|
panic("unreachable")
|
|
}
|
|
}
|
|
|
|
// Error implements FragmentIterator.
|
|
func (i *BoundedIter) Error() error {
|
|
return i.iter.Error()
|
|
}
|
|
|
|
// Close implements FragmentIterator.
|
|
func (i *BoundedIter) Close() error {
|
|
return i.iter.Close()
|
|
}
|
|
|
|
// SetBounds modifies the FragmentIterator's bounds.
|
|
func (i *BoundedIter) SetBounds(lower, upper []byte) {
|
|
i.lower, i.upper = lower, upper
|
|
}
|
|
|
|
func (i *BoundedIter) checkPrefixSpanStart(span *Span) *Span {
|
|
// Compare to the prefix's bounds, if in prefix iteration mode.
|
|
if span != nil && i.hasPrefix != nil && *i.hasPrefix {
|
|
si := i.split(span.Start)
|
|
if i.cmp(span.Start[:si], *i.prefix) > 0 {
|
|
// This span starts at a prefix that sorts after our current prefix.
|
|
span = nil
|
|
}
|
|
}
|
|
return span
|
|
}
|
|
|
|
// checkForwardBound enforces the upper bound, returning nil if the provided
|
|
// span is wholly outside the upper bound. It also updates i.pos and i.iterSpan
|
|
// to reflect the new iterator position.
|
|
func (i *BoundedIter) checkForwardBound(span *Span) *Span {
|
|
// Compare to the upper bound.
|
|
if span != nil && i.upper != nil && i.cmp(span.Start, i.upper) >= 0 {
|
|
span = nil
|
|
}
|
|
i.iterSpan = span
|
|
if i.pos != posAtIterSpan {
|
|
i.pos = posAtIterSpan
|
|
}
|
|
return span
|
|
}
|
|
|
|
func (i *BoundedIter) checkPrefixSpanEnd(span *Span) *Span {
|
|
// Compare to the prefix's bounds, if in prefix iteration mode.
|
|
if span != nil && i.hasPrefix != nil && *i.hasPrefix && i.cmp(span.End, *i.prefix) <= 0 {
|
|
// This span ends before the current prefix.
|
|
span = nil
|
|
}
|
|
return span
|
|
}
|
|
|
|
// checkBackward enforces the lower bound, returning nil if the provided span is
|
|
// wholly outside the lower bound. It also updates i.pos and i.iterSpan to
|
|
// reflect the new iterator position.
|
|
func (i *BoundedIter) checkBackwardBound(span *Span) *Span {
|
|
// Compare to the lower bound.
|
|
if span != nil && i.lower != nil && i.cmp(span.End, i.lower) <= 0 {
|
|
span = nil
|
|
}
|
|
i.iterSpan = span
|
|
if i.pos != posAtIterSpan {
|
|
i.pos = posAtIterSpan
|
|
}
|
|
return span
|
|
}
|