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iterator.go
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iterator.go
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// Copyright 2011 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 pebble
import (
"bytes"
"io"
"github.com/cockroachdb/errors"
)
type iterPos int8
const (
iterPosCur iterPos = 0
iterPosNext iterPos = 1
iterPosPrev iterPos = -1
)
var errReversePrefixIteration = errors.New("pebble: unsupported reverse prefix iteration")
// Iterator iterates over a DB's key/value pairs in key order.
//
// An iterator must be closed after use, but it is not necessary to read an
// iterator until exhaustion.
//
// An iterator is not goroutine-safe, but it is safe to use multiple iterators
// concurrently, with each in a dedicated goroutine.
//
// It is also safe to use an iterator concurrently with modifying its
// underlying DB, if that DB permits modification. However, the resultant
// key/value pairs are not guaranteed to be a consistent snapshot of that DB
// at a particular point in time.
//
// If an iterator encounters an error during any operation, it is stored by
// the Iterator and surfaced through the Error method. All absolute
// positioning methods (eg, SeekLT, SeekGT, First, Last, etc) reset any
// accumulated error before positioning. All relative positioning methods (eg,
// Next, Prev) return without advancing if the iterator has an accumulated
// error.
type Iterator struct {
opts IterOptions
cmp Compare
equal Equal
merge Merge
split Split
iter internalIterator
readState *readState
err error
key []byte
keyBuf []byte
value []byte
valueBuf []byte
valueCloser io.Closer
valid bool
iterKey *InternalKey
iterValue []byte
pos iterPos
alloc *iterAlloc
prefix []byte
}
func (i *Iterator) findNextEntry() bool {
i.valid = false
i.pos = iterPosCur
// Close the closer for the current value if one was open.
if i.valueCloser != nil {
i.err = i.valueCloser.Close()
i.valueCloser = nil
if i.err != nil {
return false
}
}
for i.iterKey != nil {
key := *i.iterKey
if i.prefix != nil {
if n := i.split(key.UserKey); !bytes.Equal(i.prefix, key.UserKey[:n]) {
return false
}
}
switch key.Kind() {
case InternalKeyKindDelete, InternalKeyKindSingleDelete:
i.nextUserKey()
continue
case InternalKeyKindSet:
i.keyBuf = append(i.keyBuf[:0], key.UserKey...)
i.key = i.keyBuf
i.value = i.iterValue
i.valid = true
return true
case InternalKeyKindMerge:
var valueMerger ValueMerger
valueMerger, i.err = i.merge(i.key, i.iterValue)
if i.err == nil {
i.mergeNext(key, valueMerger)
}
if i.err == nil {
i.value, i.valueCloser, i.err = valueMerger.Finish()
}
return i.err == nil
default:
i.err = errors.Errorf("pebble: invalid internal key kind: %d", errors.Safe(key.Kind()))
return false
}
}
return false
}
func (i *Iterator) nextUserKey() {
if i.iterKey == nil {
return
}
done := i.iterKey.SeqNum() == 0
if !i.valid {
i.keyBuf = append(i.keyBuf[:0], i.iterKey.UserKey...)
i.key = i.keyBuf
}
for {
i.iterKey, i.iterValue = i.iter.Next()
if done || i.iterKey == nil {
break
}
if !i.equal(i.key, i.iterKey.UserKey) {
break
}
done = i.iterKey.SeqNum() == 0
}
}
func (i *Iterator) findPrevEntry() bool {
i.valid = false
i.pos = iterPosCur
// Close the closer for the current value if one was open.
if i.valueCloser != nil {
i.err = i.valueCloser.Close()
i.valueCloser = nil
if i.err != nil {
return false
}
}
var valueMerger ValueMerger
for i.iterKey != nil {
key := *i.iterKey
if i.valid {
if !i.equal(key.UserKey, i.key) {
// We've iterated to the previous user key.
i.pos = iterPosPrev
if valueMerger != nil {
i.value, i.valueCloser, i.err = valueMerger.Finish()
}
return i.err == nil
}
}
switch key.Kind() {
case InternalKeyKindDelete, InternalKeyKindSingleDelete:
i.value = nil
i.valid = false
valueMerger = nil
i.iterKey, i.iterValue = i.iter.Prev()
continue
case InternalKeyKindSet:
i.keyBuf = append(i.keyBuf[:0], key.UserKey...)
i.key = i.keyBuf
// iterValue is owned by i.iter and could change after the Prev()
// call, so use valueBuf instead. Note that valueBuf is only used
// in this one instance; everywhere else (eg. in findNextEntry),
// we just point i.value to the unsafe i.iter-owned value buffer.
i.valueBuf = append(i.valueBuf[:0], i.iterValue...)
i.value = i.valueBuf
i.valid = true
i.iterKey, i.iterValue = i.iter.Prev()
valueMerger = nil
continue
case InternalKeyKindMerge:
if !i.valid {
i.keyBuf = append(i.keyBuf[:0], key.UserKey...)
i.key = i.keyBuf
valueMerger, i.err = i.merge(i.key, i.iterValue)
if i.err != nil {
return false
}
i.valid = true
} else if valueMerger == nil {
valueMerger, i.err = i.merge(i.key, i.value)
if i.err == nil {
i.err = valueMerger.MergeNewer(i.iterValue)
}
if i.err != nil {
return false
}
} else {
i.err = valueMerger.MergeNewer(i.iterValue)
if i.err != nil {
return false
}
}
i.iterKey, i.iterValue = i.iter.Prev()
continue
default:
i.err = errors.Errorf("pebble: invalid internal key kind: %d", errors.Safe(key.Kind()))
return false
}
}
if i.valid {
i.pos = iterPosPrev
if valueMerger != nil {
i.value, i.valueCloser, i.err = valueMerger.Finish()
}
return i.err == nil
}
return false
}
func (i *Iterator) prevUserKey() {
if i.iterKey == nil {
return
}
if !i.valid {
// If we're going to compare against the prev key, we need to save the
// current key.
i.keyBuf = append(i.keyBuf[:0], i.iterKey.UserKey...)
i.key = i.keyBuf
}
for {
i.iterKey, i.iterValue = i.iter.Prev()
if i.iterKey == nil {
break
}
if !i.equal(i.key, i.iterKey.UserKey) {
break
}
}
}
func (i *Iterator) mergeNext(key InternalKey, valueMerger ValueMerger) {
// Save the current key.
i.keyBuf = append(i.keyBuf[:0], key.UserKey...)
i.key = i.keyBuf
i.valid = true
// Loop looking for older values for this key and merging them.
for {
i.iterKey, i.iterValue = i.iter.Next()
if i.iterKey == nil {
i.pos = iterPosNext
return
}
key = *i.iterKey
if !i.equal(i.key, key.UserKey) {
// We've advanced to the next key.
i.pos = iterPosNext
return
}
switch key.Kind() {
case InternalKeyKindDelete, InternalKeyKindSingleDelete:
// We've hit a deletion tombstone. Return everything up to this
// point.
return
case InternalKeyKindSet:
// We've hit a Set value. Merge with the existing value and return.
i.err = valueMerger.MergeOlder(i.iterValue)
return
case InternalKeyKindMerge:
// We've hit another Merge value. Merge with the existing value and
// continue looping.
i.err = valueMerger.MergeOlder(i.iterValue)
if i.err != nil {
return
}
continue
default:
i.err = errors.Errorf("pebble: invalid internal key kind: %d", errors.Safe(key.Kind()))
return
}
}
}
// SeekGE moves the iterator to the first key/value pair whose key is greater
// than or equal to the given key. Returns true if the iterator is pointing at
// a valid entry and false otherwise.
func (i *Iterator) SeekGE(key []byte) bool {
i.err = nil // clear cached iteration error
i.prefix = nil
if lowerBound := i.opts.GetLowerBound(); lowerBound != nil && i.cmp(key, lowerBound) < 0 {
key = lowerBound
}
i.iterKey, i.iterValue = i.iter.SeekGE(key)
return i.findNextEntry()
}
// SeekPrefixGE moves the iterator to the first key/value pair whose key is
// greater than or equal to the given key and which has the same "prefix" as
// the given key. The prefix for a key is determined by the user-defined
// Comparer.Split function. The iterator will not observe keys not matching the
// "prefix" of the search key. Calling SeekPrefixGE puts the iterator in prefix
// iteration mode. The iterator remains in prefix iteration until a subsequent
// call to another absolute positioning method (SeekGE, SeekLT, First,
// Last). Reverse iteration (Prev) is not supported when an iterator is in
// prefix iteration mode. Returns true if the iterator is pointing at a valid
// entry and false otherwise.
//
// The semantics of SeekPrefixGE are slightly unusual and designed for
// iteration to be able to take advantage of bloom filters that have been
// created on the "prefix". If you're not using bloom filters, there is no
// reason to use SeekPrefixGE.
//
// An example Split function may separate a timestamp suffix from the prefix of
// the key.
//
// Split(<key>@<timestamp>) -> <key>
//
// Consider the keys "a@1", "a@2", "aa@3", "aa@4". The prefixes for these keys
// are "a", and "aa". Note that despite "a" and "aa" sharing a prefix by the
// usual definition, those prefixes differ by the definition of the Split
// function. To see how this works, consider the following set of calls on this
// data set:
//
// SeekPrefixGE("a@0") -> "a@1"
// Next() -> "a@2"
// Next() -> EOF
func (i *Iterator) SeekPrefixGE(key []byte) bool {
i.err = nil // clear cached iteration error
if i.split == nil {
panic("pebble: split must be provided for SeekPrefixGE")
}
// Make a copy of the prefix so that modifications to the key after
// SeekPrefixGE returns does not affect the stored prefix.
prefixLen := i.split(key)
i.prefix = make([]byte, prefixLen)
copy(i.prefix, key[:prefixLen])
if lowerBound := i.opts.GetLowerBound(); lowerBound != nil && i.cmp(key, lowerBound) < 0 {
if n := i.split(lowerBound); !bytes.Equal(i.prefix, lowerBound[:n]) {
i.err = errors.New("pebble: SeekPrefixGE supplied with key outside of lower bound")
return false
}
key = lowerBound
}
i.iterKey, i.iterValue = i.iter.SeekPrefixGE(i.prefix, key)
return i.findNextEntry()
}
// SeekLT moves the iterator to the last key/value pair whose key is less than
// the given key. Returns true if the iterator is pointing at a valid entry and
// false otherwise.
func (i *Iterator) SeekLT(key []byte) bool {
i.err = nil // clear cached iteration error
i.prefix = nil
if upperBound := i.opts.GetUpperBound(); upperBound != nil && i.cmp(key, upperBound) >= 0 {
key = upperBound
}
i.iterKey, i.iterValue = i.iter.SeekLT(key)
return i.findPrevEntry()
}
// First moves the iterator the the first key/value pair. Returns true if the
// iterator is pointing at a valid entry and false otherwise.
func (i *Iterator) First() bool {
i.err = nil // clear cached iteration error
i.prefix = nil
if lowerBound := i.opts.GetLowerBound(); lowerBound != nil {
i.iterKey, i.iterValue = i.iter.SeekGE(lowerBound)
} else {
i.iterKey, i.iterValue = i.iter.First()
}
return i.findNextEntry()
}
// Last moves the iterator the the last key/value pair. Returns true if the
// iterator is pointing at a valid entry and false otherwise.
func (i *Iterator) Last() bool {
i.err = nil // clear cached iteration error
i.prefix = nil
if upperBound := i.opts.GetUpperBound(); upperBound != nil {
i.iterKey, i.iterValue = i.iter.SeekLT(upperBound)
} else {
i.iterKey, i.iterValue = i.iter.Last()
}
return i.findPrevEntry()
}
// Next moves the iterator to the next key/value pair. Returns true if the
// iterator is pointing at a valid entry and false otherwise.
func (i *Iterator) Next() bool {
if i.err != nil {
return false
}
switch i.pos {
case iterPosCur:
i.nextUserKey()
case iterPosPrev:
// The underlying iterator is pointed to the previous key (this can only
// happen when switching iteration directions). We set i.valid to false
// here to force the calls to nextUserKey to save the current key i.iter is
// pointing at in order to determine when the next user-key is reached.
i.valid = false
if i.iterKey == nil {
// We're positioned before the first key. Need to reposition to point to
// the first key.
if lowerBound := i.opts.GetLowerBound(); lowerBound != nil {
i.iterKey, i.iterValue = i.iter.SeekGE(lowerBound)
} else {
i.iterKey, i.iterValue = i.iter.First()
}
} else {
i.nextUserKey()
}
i.nextUserKey()
case iterPosNext:
}
return i.findNextEntry()
}
// Prev moves the iterator to the previous key/value pair. Returns true if the
// iterator is pointing at a valid entry and false otherwise.
func (i *Iterator) Prev() bool {
if i.err != nil {
return false
}
if i.prefix != nil {
i.err = errReversePrefixIteration
return false
}
switch i.pos {
case iterPosCur:
i.prevUserKey()
case iterPosNext:
// The underlying iterator is pointed to the next key (this can only happen
// when switching iteration directions). We set i.valid to false here to
// force the calls to prevUserKey to save the current key i.iter is
// pointing at in order to determine when the prev user-key is reached.
i.valid = false
if i.iterKey == nil {
// We're positioned after the last key. Need to reposition to point to
// the last key.
if upperBound := i.opts.GetUpperBound(); upperBound != nil {
i.iterKey, i.iterValue = i.iter.SeekLT(upperBound)
} else {
i.iterKey, i.iterValue = i.iter.Last()
}
} else {
i.prevUserKey()
}
i.prevUserKey()
case iterPosPrev:
}
return i.findPrevEntry()
}
// Key returns the key of the current key/value pair, or nil if done. The
// caller should not modify the contents of the returned slice, and its
// contents may change on the next call to Next.
func (i *Iterator) Key() []byte {
return i.key
}
// Value returns the value of the current key/value pair, or nil if done. The
// caller should not modify the contents of the returned slice, and its
// contents may change on the next call to Next.
func (i *Iterator) Value() []byte {
return i.value
}
// Valid returns true if the iterator is positioned at a valid key/value pair
// and false otherwise.
func (i *Iterator) Valid() bool {
return i.valid
}
// Error returns any accumulated error.
func (i *Iterator) Error() error {
err := i.err
if i.iter != nil {
err = firstError(i.err, i.iter.Error())
}
return err
}
// Close closes the iterator and returns any accumulated error. Exhausting
// all the key/value pairs in a table is not considered to be an error.
// It is not valid to call any method, including Close, after the iterator
// has been closed.
func (i *Iterator) Close() error {
// Close the child iterator before releasing the readState because when the
// readState is released sstables referenced by the readState may be deleted
// which will fail on Windows if the sstables are still open by the child
// iterator.
if i.iter != nil {
i.err = firstError(i.err, i.iter.Close())
}
err := i.err
if i.readState != nil {
i.readState.unref()
i.readState = nil
}
// Close the closer for the current value if one was open.
if i.valueCloser != nil {
err = firstError(err, i.valueCloser.Close())
i.valueCloser = nil
}
if alloc := i.alloc; alloc != nil {
*i = Iterator{}
iterAllocPool.Put(alloc)
}
return err
}
// SetBounds sets the lower and upper bounds for the iterator. Note that the
// iterator will always be invalidated and must be repositioned with a call to
// SeekGE, SeekPrefixGE, SeekLT, First, or Last.
func (i *Iterator) SetBounds(lower, upper []byte) {
i.prefix = nil
i.iterKey = nil
i.iterValue = nil
i.pos = iterPosCur
i.valid = false
i.opts.LowerBound = lower
i.opts.UpperBound = upper
i.iter.SetBounds(lower, upper)
}