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2022-09-04 02:34:54 +03:00
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// 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 pebble
import (
"io"
"sort"
"strconv"
"github.com/cockroachdb/errors"
"github.com/cockroachdb/pebble/internal/base"
"github.com/cockroachdb/pebble/internal/bytealloc"
"github.com/cockroachdb/pebble/internal/keyspan"
"github.com/cockroachdb/pebble/internal/rangekey"
)
// compactionIter provides a forward-only iterator that encapsulates the logic
// for collapsing entries during compaction. It wraps an internal iterator and
// collapses entries that are no longer necessary because they are shadowed by
// newer entries. The simplest example of this is when the internal iterator
// contains two keys: a.PUT.2 and a.PUT.1. Instead of returning both entries,
// compactionIter collapses the second entry because it is no longer
// necessary. The high-level structure for compactionIter is to iterate over
// its internal iterator and output 1 entry for every user-key. There are four
// complications to this story.
//
// 1. Eliding Deletion Tombstones
//
// Consider the entries a.DEL.2 and a.PUT.1. These entries collapse to
// a.DEL.2. Do we have to output the entry a.DEL.2? Only if a.DEL.2 possibly
// shadows an entry at a lower level. If we're compacting to the base-level in
// the LSM tree then a.DEL.2 is definitely not shadowing an entry at a lower
// level and can be elided.
//
// We can do slightly better than only eliding deletion tombstones at the base
// level by observing that we can elide a deletion tombstone if there are no
// sstables that contain the entry's key. This check is performed by
// elideTombstone.
//
// 2. Merges
//
// The MERGE operation merges the value for an entry with the existing value
// for an entry. The logical value of an entry can be composed of a series of
// merge operations. When compactionIter sees a MERGE, it scans forward in its
// internal iterator collapsing MERGE operations for the same key until it
// encounters a SET or DELETE operation. For example, the keys a.MERGE.4,
// a.MERGE.3, a.MERGE.2 will be collapsed to a.MERGE.4 and the values will be
// merged using the specified Merger.
//
// An interesting case here occurs when MERGE is combined with SET. Consider
// the entries a.MERGE.3 and a.SET.2. The collapsed key will be a.SET.3. The
// reason that the kind is changed to SET is because the SET operation acts as
// a barrier preventing further merging. This can be seen better in the
// scenario a.MERGE.3, a.SET.2, a.MERGE.1. The entry a.MERGE.1 may be at lower
// (older) level and not involved in the compaction. If the compaction of
// a.MERGE.3 and a.SET.2 produced a.MERGE.3, a subsequent compaction with
// a.MERGE.1 would merge the values together incorrectly.
//
// 3. Snapshots
//
// Snapshots are lightweight point-in-time views of the DB state. At its core,
// a snapshot is a sequence number along with a guarantee from Pebble that it
// will maintain the view of the database at that sequence number. Part of this
// guarantee is relatively straightforward to achieve. When reading from the
// database Pebble will ignore sequence numbers that are larger than the
// snapshot sequence number. The primary complexity with snapshots occurs
// during compaction: the collapsing of entries that are shadowed by newer
// entries is at odds with the guarantee that Pebble will maintain the view of
// the database at the snapshot sequence number. Rather than collapsing entries
// up to the next user key, compactionIter can only collapse entries up to the
// next snapshot boundary. That is, every snapshot boundary potentially causes
// another entry for the same user-key to be emitted. Another way to view this
// is that snapshots define stripes and entries are collapsed within stripes,
// but not across stripes. Consider the following scenario:
//
// a.PUT.9
// a.DEL.8
// a.PUT.7
// a.DEL.6
// a.PUT.5
//
// In the absence of snapshots these entries would be collapsed to
// a.PUT.9. What if there is a snapshot at sequence number 7? The entries can
// be divided into two stripes and collapsed within the stripes:
//
// a.PUT.9 a.PUT.9
// a.DEL.8 --->
// a.PUT.7
// -- --
// a.DEL.6 ---> a.DEL.6
// a.PUT.5
//
// All of the rules described earlier still apply, but they are confined to
// operate within a snapshot stripe. Snapshots only affect compaction when the
// snapshot sequence number lies within the range of sequence numbers being
// compacted. In the above example, a snapshot at sequence number 10 or at
// sequence number 5 would not have any effect.
//
// 4. Range Deletions
//
// Range deletions provide the ability to delete all of the keys (and values)
// in a contiguous range. Range deletions are stored indexed by their start
// key. The end key of the range is stored in the value. In order to support
// lookup of the range deletions which overlap with a particular key, the range
// deletion tombstones need to be fragmented whenever they overlap. This
// fragmentation is performed by keyspan.Fragmenter. The fragments are then
// subject to the rules for snapshots. For example, consider the two range
// tombstones [a,e)#1 and [c,g)#2:
//
// 2: c-------g
// 1: a-------e
//
// These tombstones will be fragmented into:
//
// 2: c---e---g
// 1: a---c---e
//
// Do we output the fragment [c,e)#1? Since it is covered by [c-e]#2 the answer
// depends on whether it is in a new snapshot stripe.
//
// In addition to the fragmentation of range tombstones, compaction also needs
// to take the range tombstones into consideration when outputting normal
// keys. Just as with point deletions, a range deletion covering an entry can
// cause the entry to be elided.
//
// A note on the stability of keys and values.
//
// The stability guarantees of keys and values returned by the iterator tree
// that backs a compactionIter is nuanced and care must be taken when
// referencing any returned items.
//
// Keys and values returned by exported functions (i.e. First, Next, etc.) have
// lifetimes that fall into two categories:
//
// Lifetime valid for duration of compaction. Range deletion keys and values are
// stable for the duration of the compaction, due to way in which a
// compactionIter is typically constructed (i.e. via (*compaction).newInputIter,
// which wraps the iterator over the range deletion block in a noCloseIter,
// preventing the release of the backing memory until the compaction is
// finished).
//
// Lifetime limited to duration of sstable block liveness. Point keys (SET, DEL,
// etc.) and values must be cloned / copied following the return from the
// exported function, and before a subsequent call to Next advances the iterator
// and mutates the contents of the returned key and value.
type compactionIter struct {
equal Equal
merge Merge
iter internalIterator
err error
// `key.UserKey` is set to `keyBuf` caused by saving `i.iterKey.UserKey`
// and `key.Trailer` is set to `i.iterKey.Trailer`. This is the
// case on return from all public methods -- these methods return `key`.
// Additionally, it is the internal state when the code is moving to the
// next key so it can determine whether the user key has changed from
// the previous key.
key InternalKey
value []byte
valueCloser io.Closer
// Temporary buffer used for storing the previous user key in order to
// determine when iteration has advanced to a new user key and thus a new
// snapshot stripe.
keyBuf []byte
// Temporary buffer used for storing the previous value, which may be an
// unsafe, i.iter-owned slice that could be altered when the iterator is
// advanced.
valueBuf []byte
// Is the current entry valid?
valid bool
iterKey *InternalKey
iterValue []byte
// `skip` indicates whether the remaining skippable entries in the current
// snapshot stripe should be skipped or processed. An example of a non-
// skippable entry is a range tombstone as we need to return it from the
// `compactionIter`, even if a key covering its start key has already been
// seen in the same stripe. `skip` has no effect when `pos == iterPosNext`.
skip bool
// `pos` indicates the iterator position at the top of `Next()`. Its type's
// (`iterPos`) values take on the following meanings in the context of
// `compactionIter`.
//
// - `iterPosCur`: the iterator is at the last key returned.
// - `iterPosNext`: the iterator has already been advanced to the next
// candidate key. For example, this happens when processing merge operands,
// where we advance the iterator all the way into the next stripe or next
// user key to ensure we've seen all mergeable operands.
// - `iterPosPrev`: this is invalid as compactionIter is forward-only.
pos iterPos
// The index of the snapshot for the current key within the snapshots slice.
curSnapshotIdx int
curSnapshotSeqNum uint64
// The snapshot sequence numbers that need to be maintained. These sequence
// numbers define the snapshot stripes (see the Snapshots description
// above). The sequence numbers are in ascending order.
snapshots []uint64
// Reference to the range deletion tombstone fragmenter (e.g.,
// `compaction.rangeDelFrag`).
rangeDelFrag *keyspan.Fragmenter
rangeKeyFrag *keyspan.Fragmenter
// The fragmented tombstones.
tombstones []keyspan.Span
// The fragmented range keys.
rangeKeys []keyspan.Span
// Byte allocator for the tombstone keys.
alloc bytealloc.A
allowZeroSeqNum bool
elideTombstone func(key []byte) bool
elideRangeTombstone func(start, end []byte) bool
// The on-disk format major version. This informs the types of keys that
// may be written to disk during a compaction.
formatVersion FormatMajorVersion
}
func newCompactionIter(
cmp Compare,
equal Equal,
formatKey base.FormatKey,
merge Merge,
iter internalIterator,
snapshots []uint64,
rangeDelFrag *keyspan.Fragmenter,
rangeKeyFrag *keyspan.Fragmenter,
allowZeroSeqNum bool,
elideTombstone func(key []byte) bool,
elideRangeTombstone func(start, end []byte) bool,
formatVersion FormatMajorVersion,
) *compactionIter {
i := &compactionIter{
equal: equal,
merge: merge,
iter: iter,
snapshots: snapshots,
rangeDelFrag: rangeDelFrag,
rangeKeyFrag: rangeKeyFrag,
allowZeroSeqNum: allowZeroSeqNum,
elideTombstone: elideTombstone,
elideRangeTombstone: elideRangeTombstone,
formatVersion: formatVersion,
}
i.rangeDelFrag.Cmp = cmp
i.rangeDelFrag.Format = formatKey
i.rangeDelFrag.Emit = i.emitRangeDelChunk
i.rangeKeyFrag.Cmp = cmp
i.rangeKeyFrag.Format = formatKey
i.rangeKeyFrag.Emit = i.emitRangeKeyChunk
return i
}
func (i *compactionIter) First() (*InternalKey, []byte) {
if i.err != nil {
return nil, nil
}
i.iterKey, i.iterValue = i.iter.First()
if i.iterKey != nil {
i.curSnapshotIdx, i.curSnapshotSeqNum = snapshotIndex(i.iterKey.SeqNum(), i.snapshots)
}
i.pos = iterPosNext
return i.Next()
}
func (i *compactionIter) Next() (*InternalKey, []byte) {
if i.err != nil {
return nil, nil
}
// Close the closer for the current value if one was open.
if i.closeValueCloser() != nil {
return nil, nil
}
// Prior to this call to `Next()` we are in one of three situations with
// respect to `iterKey` and related state:
//
// - `!skip && pos == iterPosNext`: `iterKey` is already at the next key.
// - `!skip && pos == iterPosCur`: We are at the key that has been returned.
// To move forward we advance by one key, even if that lands us in the same
// snapshot stripe.
// - `skip && pos == iterPosCur`: We are at the key that has been returned.
// To move forward we skip skippable entries in the stripe.
if i.pos == iterPosCurForward {
if i.skip {
i.skipInStripe()
} else {
i.nextInStripe()
}
}
i.pos = iterPosCurForward
i.valid = false
for i.iterKey != nil {
if i.iterKey.Kind() == InternalKeyKindRangeDelete || rangekey.IsRangeKey(i.iterKey.Kind()) {
// Return the span so the compaction can use it for file truncation and add
// it to the relevant fragmenter. We do not set `skip` to true before
// returning as there may be a forthcoming point key with the same user key
// and sequence number. Such a point key must be visible (i.e., not skipped
// over) since we promise point keys are not deleted by range tombstones at
// the same sequence number.
//
// Although, note that `skip` may already be true before reaching here
// due to an earlier key in the stripe. Then it is fine to leave it set
// to true, as the earlier key must have had a higher sequence number.
//
// NOTE: there is a subtle invariant violation here in that calling
// saveKey and returning a reference to the temporary slice violates
// the stability guarantee for range deletion keys. A potential
// mediation could return the original iterKey and iterValue
// directly, as the backing memory is guaranteed to be stable until
// the compaction completes. The violation here is only minor in
// that the caller immediately clones the range deletion InternalKey
// when passing the key to the deletion fragmenter (see the
// call-site in compaction.go).
// TODO(travers): address this violation by removing the call to
// saveKey and instead return the original iterKey and iterValue.
// This goes against the comment on i.key in the struct, and
// therefore warrants some investigation.
i.saveKey()
i.value = i.iterValue
i.valid = true
return &i.key, i.value
}
if i.rangeDelFrag.Covers(*i.iterKey, i.curSnapshotSeqNum) {
i.saveKey()
i.skipInStripe()
continue
}
switch i.iterKey.Kind() {
case InternalKeyKindDelete, InternalKeyKindSingleDelete:
// If we're at the last snapshot stripe and the tombstone can be elided
// skip skippable keys in the same stripe.
if i.curSnapshotIdx == 0 && i.elideTombstone(i.iterKey.UserKey) {
i.saveKey()
i.skipInStripe()
continue
}
switch i.iterKey.Kind() {
case InternalKeyKindDelete:
i.saveKey()
i.value = i.iterValue
i.valid = true
i.skip = true
return &i.key, i.value
case InternalKeyKindSingleDelete:
if i.singleDeleteNext() {
return &i.key, i.value
}
continue
}
case InternalKeyKindSet, InternalKeyKindSetWithDelete:
// The key we emit for this entry is a function of the current key
// kind, and whether this entry is followed by a DEL/SINGLEDEL
// entry. setNext() does the work to move the iterator forward,
// preserving the original value, and potentially mutating the key
// kind.
i.setNext()
return &i.key, i.value
case InternalKeyKindMerge:
// Record the snapshot index before mergeNext as merging
// advances the iterator, adjusting curSnapshotIdx.
origSnapshotIdx := i.curSnapshotIdx
var valueMerger ValueMerger
valueMerger, i.err = i.merge(i.iterKey.UserKey, i.iterValue)
var change stripeChangeType
if i.err == nil {
change = i.mergeNext(valueMerger)
}
var needDelete bool
if i.err == nil {
// includesBase is true whenever we've transformed the MERGE record
// into a SET.
includesBase := i.key.Kind() == InternalKeyKindSet
i.value, needDelete, i.valueCloser, i.err = finishValueMerger(valueMerger, includesBase)
}
if i.err == nil {
if needDelete {
i.valid = false
if i.closeValueCloser() != nil {
return nil, nil
}
continue
}
// A non-skippable entry does not necessarily cover later merge
// operands, so we must not zero the current merge result's seqnum.
//
// For example, suppose the forthcoming two keys are a range
// tombstone, `[a, b)#3`, and a merge operand, `a#3`. Recall that
// range tombstones do not cover point keys at the same seqnum, so
// `a#3` is not deleted. The range tombstone will be seen first due
// to its larger value type. Since it is a non-skippable key, the
// current merge will not include `a#3`. If we zeroed the current
// merge result's seqnum, then it would conflict with the upcoming
// merge including `a#3`, whose seqnum will also be zeroed.
if change != sameStripeNonSkippable {
i.maybeZeroSeqnum(origSnapshotIdx)
}
return &i.key, i.value
}
if i.err != nil {
i.valid = false
i.err = base.MarkCorruptionError(i.err)
}
return nil, nil
default:
i.err = base.CorruptionErrorf("invalid internal key kind: %d", errors.Safe(i.iterKey.Kind()))
i.valid = false
return nil, nil
}
}
return nil, nil
}
func (i *compactionIter) closeValueCloser() error {
if i.valueCloser == nil {
return nil
}
i.err = i.valueCloser.Close()
i.valueCloser = nil
if i.err != nil {
i.valid = false
}
return i.err
}
// snapshotIndex returns the index of the first sequence number in snapshots
// which is greater than or equal to seq.
func snapshotIndex(seq uint64, snapshots []uint64) (int, uint64) {
index := sort.Search(len(snapshots), func(i int) bool {
return snapshots[i] > seq
})
if index >= len(snapshots) {
return index, InternalKeySeqNumMax
}
return index, snapshots[index]
}
// skipInStripe skips over skippable keys in the same stripe and user key.
func (i *compactionIter) skipInStripe() {
i.skip = true
var change stripeChangeType
for {
change = i.nextInStripe()
if change == sameStripeNonSkippable || change == newStripe {
break
}
}
// Reset skip if we landed outside the original stripe. Otherwise, we landed
// in the same stripe on a non-skippable key. In that case we should preserve
// `i.skip == true` such that later keys in the stripe will continue to be
// skipped.
if change == newStripe {
i.skip = false
}
}
func (i *compactionIter) iterNext() bool {
i.iterKey, i.iterValue = i.iter.Next()
return i.iterKey != nil
}
// stripeChangeType indicates how the snapshot stripe changed relative to the previous
// key. If no change, it also indicates whether the current entry is skippable.
type stripeChangeType int
const (
newStripe stripeChangeType = iota
sameStripeSkippable
sameStripeNonSkippable
)
// nextInStripe advances the iterator and returns one of the above const ints
// indicating how its state changed.
//
// Calls to nextInStripe must be preceded by a call to saveKey to retain a
// temporary reference to the original key, so that forward iteration can
// proceed with a reference to the original key. Care should be taken to avoid
// overwriting or mutating the saved key or value before they have been returned
// to the caller of the exported function (i.e. the caller of Next, First, etc.)
func (i *compactionIter) nextInStripe() stripeChangeType {
if !i.iterNext() {
return newStripe
}
key := i.iterKey
if !i.equal(i.key.UserKey, key.UserKey) {
i.curSnapshotIdx, i.curSnapshotSeqNum = snapshotIndex(key.SeqNum(), i.snapshots)
return newStripe
}
origSnapshotIdx := i.curSnapshotIdx
i.curSnapshotIdx, i.curSnapshotSeqNum = snapshotIndex(key.SeqNum(), i.snapshots)
switch key.Kind() {
case InternalKeyKindRangeDelete:
// Range tombstones need to be exposed by the compactionIter to the upper level
// `compaction` object, so return them regardless of whether they are in the same
// snapshot stripe.
if i.curSnapshotIdx == origSnapshotIdx {
return sameStripeNonSkippable
}
return newStripe
case InternalKeyKindRangeKeySet, InternalKeyKindRangeKeyUnset, InternalKeyKindRangeKeyDelete:
// Range keys are interleaved at the max sequence number for a given user
// key, so we should not see any more range keys in this stripe.
panic("unreachable")
case InternalKeyKindInvalid:
if i.curSnapshotIdx == origSnapshotIdx {
return sameStripeNonSkippable
}
return newStripe
}
if i.curSnapshotIdx == origSnapshotIdx {
return sameStripeSkippable
}
return newStripe
}
func (i *compactionIter) setNext() {
// Save the current key.
i.saveKey()
i.value = i.iterValue
i.valid = true
i.maybeZeroSeqnum(i.curSnapshotIdx)
// There are two cases where we can early return and skip the remaining
// records in the stripe:
// - If the DB does not SETWITHDEL.
// - If this key is already a SETWITHDEL.
if i.formatVersion < FormatSetWithDelete ||
i.iterKey.Kind() == InternalKeyKindSetWithDelete {
i.skip = true
return
}
// We are iterating forward. Save the current value.
i.valueBuf = append(i.valueBuf[:0], i.iterValue...)
i.value = i.valueBuf
// Else, we continue to loop through entries in the stripe looking for a
// DEL. Note that we may stop *before* encountering a DEL, if one exists.
for {
switch t := i.nextInStripe(); t {
case newStripe, sameStripeNonSkippable:
i.pos = iterPosNext
if t == sameStripeNonSkippable {
// We iterated onto a key that we cannot skip. We can
// conservatively transform the original SET into a SETWITHDEL
// as an indication that there *may* still be a DEL/SINGLEDEL
// under this SET, even if we did not actually encounter one.
//
// This is safe to do, as:
//
// - in the case that there *is not* actually a DEL/SINGLEDEL
// under this entry, any SINGLEDEL above this now-transformed
// SETWITHDEL will become a DEL when the two encounter in a
// compaction. The DEL will eventually be elided in a
// subsequent compaction. The cost for ensuring correctness is
// that this entry is kept around for an additional compaction
// cycle(s).
//
// - in the case there *is* indeed a DEL/SINGLEDEL under us
// (but in a different stripe or sstable), then we will have
// already done the work to transform the SET into a
// SETWITHDEL, and we will skip any additional iteration when
// this entry is encountered again in a subsequent compaction.
//
// Ideally, this codepath would be smart enough to handle the
// case of SET <- RANGEDEL <- ... <- DEL/SINGLEDEL <- ....
// This requires preserving any RANGEDEL entries we encounter
// along the way, then emitting the original (possibly
// transformed) key, followed by the RANGEDELs. This requires
// a sizable refactoring of the existing code, as nextInStripe
// currently returns a sameStripeNonSkippable when it
// encounters a RANGEDEL.
// TODO(travers): optimize to handle the RANGEDEL case if it
// turns out to be a performance problem.
i.key.SetKind(InternalKeyKindSetWithDelete)
// By setting i.skip=true, we are saying that after the
// non-skippable key is emitted (which is likely a RANGEDEL),
// the remaining point keys that share the same user key as this
// saved key should be skipped.
i.skip = true
}
return
case sameStripeSkippable:
// We're still in the same stripe. If this is a DEL/SINGLEDEL, we
// stop looking and emit a SETWITHDEL. Subsequent keys are
// eligible for skipping.
if i.iterKey.Kind() == InternalKeyKindDelete ||
i.iterKey.Kind() == InternalKeyKindSingleDelete {
i.key.SetKind(InternalKeyKindSetWithDelete)
i.skip = true
return
}
default:
panic("pebble: unexpected stripeChangeType: " + strconv.Itoa(int(t)))
}
}
}
func (i *compactionIter) mergeNext(valueMerger ValueMerger) stripeChangeType {
// Save the current key.
i.saveKey()
i.valid = true
// Loop looking for older values in the current snapshot stripe and merge
// them.
for {
if change := i.nextInStripe(); change == sameStripeNonSkippable || change == newStripe {
i.pos = iterPosNext
return change
}
key := i.iterKey
switch key.Kind() {
case InternalKeyKindDelete, InternalKeyKindSingleDelete:
// We've hit a deletion tombstone. Return everything up to this point and
// then skip entries until the next snapshot stripe. We change the kind
// of the result key to a Set so that it shadows keys in lower
// levels. That is, MERGE+DEL -> SET.
// We do the same for SingleDelete since SingleDelete is only
// permitted (with deterministic behavior) for keys that have been
// set once since the last SingleDelete/Delete, so everything
// older is acceptable to shadow. Note that this is slightly
// different from singleDeleteNext() which implements stricter
// semantics in terms of applying the SingleDelete to the single
// next Set. But those stricter semantics are not observable to
// the end-user since Iterator interprets SingleDelete as Delete.
// We could do something more complicated here and consume only a
// single Set, and then merge in any following Sets, but that is
// complicated wrt code and unnecessary given the narrow permitted
// use of SingleDelete.
i.key.SetKind(InternalKeyKindSet)
i.skip = true
return sameStripeSkippable
case InternalKeyKindSet, InternalKeyKindSetWithDelete:
if i.rangeDelFrag.Covers(*key, i.curSnapshotSeqNum) {
// We change the kind of the result key to a Set so that it shadows
// keys in lower levels. That is, MERGE+RANGEDEL -> SET. This isn't
// strictly necessary, but provides consistency with the behavior of
// MERGE+DEL.
i.key.SetKind(InternalKeyKindSet)
i.skip = true
return sameStripeSkippable
}
// We've hit a Set or SetWithDel value. Merge with the existing
// value and return. We change the kind of the resulting key to a
// Set so that it shadows keys in lower levels. That is:
// MERGE + (SET*) -> SET.
i.err = valueMerger.MergeOlder(i.iterValue)
if i.err != nil {
i.valid = false
return sameStripeSkippable
}
i.key.SetKind(InternalKeyKindSet)
i.skip = true
return sameStripeSkippable
case InternalKeyKindMerge:
if i.rangeDelFrag.Covers(*key, i.curSnapshotSeqNum) {
// We change the kind of the result key to a Set so that it shadows
// keys in lower levels. That is, MERGE+RANGEDEL -> SET. This isn't
// strictly necessary, but provides consistency with the behavior of
// MERGE+DEL.
i.key.SetKind(InternalKeyKindSet)
i.skip = true
return sameStripeSkippable
}
// We've hit another Merge value. Merge with the existing value and
// continue looping.
i.err = valueMerger.MergeOlder(i.iterValue)
if i.err != nil {
i.valid = false
return sameStripeSkippable
}
default:
i.err = base.CorruptionErrorf("invalid internal key kind: %d", errors.Safe(i.iterKey.Kind()))
i.valid = false
return sameStripeSkippable
}
}
}
func (i *compactionIter) singleDeleteNext() bool {
// Save the current key.
i.saveKey()
i.value = i.iterValue
i.valid = true
// Loop until finds a key to be passed to the next level.
for {
if change := i.nextInStripe(); change == sameStripeNonSkippable || change == newStripe {
i.pos = iterPosNext
return true
}
key := i.iterKey
switch key.Kind() {
case InternalKeyKindDelete, InternalKeyKindMerge, InternalKeyKindSetWithDelete:
// We've hit a Delete, Merge or SetWithDelete, transform the
// SingleDelete into a full Delete.
i.key.SetKind(InternalKeyKindDelete)
i.skip = true
return true
case InternalKeyKindSet:
i.nextInStripe()
i.valid = false
return false
case InternalKeyKindSingleDelete:
continue
default:
i.err = base.CorruptionErrorf("invalid internal key kind: %d", errors.Safe(i.iterKey.Kind()))
i.valid = false
return false
}
}
}
func (i *compactionIter) saveKey() {
i.keyBuf = append(i.keyBuf[:0], i.iterKey.UserKey...)
i.key.UserKey = i.keyBuf
i.key.Trailer = i.iterKey.Trailer
}
func (i *compactionIter) cloneKey(key []byte) []byte {
i.alloc, key = i.alloc.Copy(key)
return key
}
func (i *compactionIter) Key() InternalKey {
return i.key
}
func (i *compactionIter) Value() []byte {
return i.value
}
func (i *compactionIter) Valid() bool {
return i.valid
}
func (i *compactionIter) Error() error {
return i.err
}
func (i *compactionIter) Close() error {
err := i.iter.Close()
if i.err == nil {
i.err = err
}
// Close the closer for the current value if one was open.
if i.valueCloser != nil {
i.err = firstError(i.err, i.valueCloser.Close())
i.valueCloser = nil
}
return i.err
}
// Tombstones returns a list of pending range tombstones in the fragmenter
// up to the specified key, or all pending range tombstones if key = nil.
func (i *compactionIter) Tombstones(key []byte) []keyspan.Span {
if key == nil {
i.rangeDelFrag.Finish()
} else {
// The specified end key is exclusive; no versions of the specified
// user key (including range tombstones covering that key) should
// be flushed yet.
i.rangeDelFrag.TruncateAndFlushTo(key)
}
tombstones := i.tombstones
i.tombstones = nil
return tombstones
}
// RangeKeys returns a list of pending fragmented range keys up to the specified
// key, or all pending range keys if key = nil.
func (i *compactionIter) RangeKeys(key []byte) []keyspan.Span {
if key == nil {
i.rangeKeyFrag.Finish()
} else {
// The specified end key is exclusive; no versions of the specified
// user key (including range tombstones covering that key) should
// be flushed yet.
i.rangeKeyFrag.TruncateAndFlushTo(key)
}
rangeKeys := i.rangeKeys
i.rangeKeys = nil
return rangeKeys
}
func (i *compactionIter) emitRangeDelChunk(fragmented keyspan.Span) {
// Apply the snapshot stripe rules, keeping only the latest tombstone for
// each snapshot stripe.
currentIdx := -1
keys := fragmented.Keys[:0]
for _, k := range fragmented.Keys {
idx, _ := snapshotIndex(k.SeqNum(), i.snapshots)
if currentIdx == idx {
continue
}
if idx == 0 && i.elideRangeTombstone(fragmented.Start, fragmented.End) {
// This is the last snapshot stripe and the range tombstone
// can be elided.
break
}
keys = append(keys, k)
if idx == 0 {
// This is the last snapshot stripe.
break
}
currentIdx = idx
}
if len(keys) > 0 {
i.tombstones = append(i.tombstones, keyspan.Span{
Start: fragmented.Start,
End: fragmented.End,
Keys: keys,
})
}
}
func (i *compactionIter) emitRangeKeyChunk(fragmented keyspan.Span) {
// Elision of snapshot stripes happens in rangeKeyCompactionTransform, so no need to
// do that here.
if len(fragmented.Keys) > 0 {
i.rangeKeys = append(i.rangeKeys, fragmented)
}
}
// maybeZeroSeqnum attempts to set the seqnum for the current key to 0. Doing
// so improves compression and enables an optimization during forward iteration
// to skip some key comparisons. The seqnum for an entry can be zeroed if the
// entry is on the bottom snapshot stripe and on the bottom level of the LSM.
func (i *compactionIter) maybeZeroSeqnum(snapshotIdx int) {
if !i.allowZeroSeqNum {
// TODO(peter): allowZeroSeqNum applies to the entire compaction. We could
// make the determination on a key by key basis, similar to what is done
// for elideTombstone. Need to add a benchmark for compactionIter to verify
// that isn't too expensive.
return
}
if snapshotIdx > 0 {
// This is not the last snapshot
return
}
i.key.SetSeqNum(0)
}