writer.go

// 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 sstable

import (
	"bufio"
	"bytes"
	"encoding/binary"
	"fmt"
	"io"
	"math"
	"sync"

	"github.com/cespare/xxhash/v2"
	"github.com/cockroachdb/errors"
	"github.com/cockroachdb/pebble/internal/base"
	"github.com/cockroachdb/pebble/internal/cache"
	"github.com/cockroachdb/pebble/internal/crc"
	"github.com/cockroachdb/pebble/internal/keyspan"
	"github.com/cockroachdb/pebble/internal/private"
	"github.com/cockroachdb/pebble/internal/rangekey"
)

var errWriterClosed = errors.New("pebble: writer is closed")

// WriterMetadata holds info about a finished sstable.
type WriterMetadata struct {
	Size             uint64
	SmallestPoint    InternalKey
	SmallestRangeDel InternalKey
	SmallestRangeKey InternalKey
	LargestPoint     InternalKey
	LargestRangeDel  InternalKey
	LargestRangeKey  InternalKey
	SmallestSeqNum   uint64
	LargestSeqNum    uint64
	Properties       Properties
}

func (m *WriterMetadata) updateSeqNum(seqNum uint64) {
	if m.SmallestSeqNum > seqNum {
		m.SmallestSeqNum = seqNum
	}
	if m.LargestSeqNum < seqNum {
		m.LargestSeqNum = seqNum
	}
}

// SmallestPointKey returns the smaller of SmallestPoint and SmallestRangeDel.
func (m *WriterMetadata) SmallestPointKey(cmp Compare) InternalKey {
	if m.SmallestPoint.UserKey == nil {
		return m.SmallestRangeDel
	}
	if m.SmallestRangeDel.UserKey == nil {
		return m.SmallestPoint
	}
	if base.InternalCompare(cmp, m.SmallestPoint, m.SmallestRangeDel) < 0 {
		return m.SmallestPoint
	}
	return m.SmallestRangeDel
}

// LargestPointKey returns the larger of LargestPoint and LargestRangeDel.
func (m *WriterMetadata) LargestPointKey(cmp Compare) InternalKey {
	if m.LargestPoint.UserKey == nil {
		return m.LargestRangeDel
	}
	if m.LargestRangeDel.UserKey == nil {
		return m.LargestPoint
	}
	if base.InternalCompare(cmp, m.LargestPoint, m.LargestRangeDel) > 0 {
		return m.LargestPoint
	}
	return m.LargestRangeDel
}

// Smallest returns the smaller of SmallestPointKey and SmallestRangeKey.
func (m *WriterMetadata) Smallest(cmp Compare) InternalKey {
	point := m.SmallestPointKey(cmp)
	if point.UserKey == nil {
		return m.SmallestRangeKey
	}
	if m.SmallestRangeKey.UserKey == nil {
		return point
	}
	if base.InternalCompare(cmp, point, m.SmallestRangeKey) < 0 {
		return point
	}
	return m.SmallestRangeKey
}

// Largest returns the larger of LargestPointKey and LargestRangeKey.
func (m *WriterMetadata) Largest(cmp Compare) InternalKey {
	point := m.LargestPointKey(cmp)
	if point.UserKey == nil {
		return m.LargestRangeKey
	}
	if m.LargestRangeKey.UserKey == nil {
		return point
	}
	if base.InternalCompare(cmp, point, m.LargestRangeKey) > 0 {
		return point
	}
	return m.LargestRangeKey
}

type flusher interface {
	Flush() error
}

type writeCloseSyncer interface {
	io.WriteCloser
	Sync() error
}

// Writer is a table writer.
type Writer struct {
	writer    io.Writer
	bufWriter *bufio.Writer
	syncer    writeCloseSyncer
	meta      WriterMetadata
	err       error
	// cacheID and fileNum are used to remove blocks written to the sstable from
	// the cache, providing a defense in depth against bugs which cause cache
	// collisions.
	cacheID uint64
	fileNum base.FileNum
	// The following fields are copied from Options.
	blockSize               int
	blockSizeThreshold      int
	indexBlockSize          int
	indexBlockSizeThreshold int
	compare                 Compare
	split                   Split
	formatKey               base.FormatKey
	compression             Compression
	separator               Separator
	successor               Successor
	tableFormat             TableFormat
	cache                   *cache.Cache
	restartInterval         int
	checksumType            ChecksumType
	// disableKeyOrderChecks disables the checks that keys are added to an
	// sstable in order. It is intended for internal use only in the construction
	// of invalid sstables for testing. See tool/make_test_sstables.go.
	disableKeyOrderChecks bool
	// With two level indexes, the index/filter of a SST file is partitioned into
	// smaller blocks with an additional top-level index on them. When reading an
	// index/filter, only the top-level index is loaded into memory. The two level
	// index/filter then uses the top-level index to load on demand into the block
	// cache the partitions that are required to perform the index/filter query.
	//
	// Two level indexes are enabled automatically when there is more than one
	// index block.
	//
	// This is useful when there are very large index blocks, which generally occurs
	// with the usage of large keys. With large index blocks, the index blocks fight
	// the data blocks for block cache space and the index blocks are likely to be
	// re-read many times from the disk. The top level index, which has a much
	// smaller memory footprint, can be used to prevent the entire index block from
	// being loaded into the block cache.
	twoLevelIndex bool
	// Internal flag to allow creation of range-del-v1 format blocks. Only used
	// for testing. Note that v2 format blocks are backwards compatible with v1
	// format blocks.
	rangeDelV1Format    bool
	indexBlock          indexBlockBuf
	rangeDelBlock       blockWriter
	rangeKeyBlock       blockWriter
	topLevelIndexBlock  blockWriter
	props               Properties
	propCollectors      []TablePropertyCollector
	blockPropCollectors []BlockPropertyCollector
	blockPropsEncoder   blockPropertiesEncoder
	// filter accumulates the filter block. If populated, the filter ingests
	// either the output of w.split (i.e. a prefix extractor) if w.split is not
	// nil, or the full keys otherwise.
	filter          filterWriter
	indexPartitions []indexBlockAndBlockProperties

	// sepScratch is reusable scratch space for computing separator keys.
	sepScratch []byte

	// indexBlockAlloc is used to bulk-allocate byte slices used to store index
	// blocks in indexPartitions. These live until the index finishes.
	indexBlockAlloc []byte
	// indexSepAlloc is used to bulk-allocate index block seperator slices stored
	// in indexPartitions. These live until the index finishes.
	indexSepAlloc []byte

	// To allow potentially overlapping (i.e. un-fragmented) range keys spans to
	// be added to the Writer, a keyspan.Fragmenter and rangekey.Coalescer are
	// used to retain the keys and values, emitting fragmented, coalesced spans as
	// appropriate. Range keys must be added in order of their start user-key.
	fragmenter keyspan.Fragmenter
	coalescer  rangekey.Coalescer
	rkBuf      []byte
	// dataBlockBuf consists of the state which is currently owned by and used by
	// the Writer client goroutine. This state can be handed off to other goroutines.
	dataBlockBuf *dataBlockBuf
	// blockBuf consists of the state which is owned by and used by the Writer client
	// goroutine.
	blockBuf blockBuf

	coordination struct {
		// writeQueue is used to write data blocks to disk. The writeQueue is primarily
		// used to maintain the order in which data blocks must be written to disk. For
		// this reason, every single data block write must be done through the writeQueue.
		writeQueue *writeQueue

		sizeEstimate sizeEstimate
	}
}

type indexBlockBuf struct {
	// block will only be accessed from the writeQueue goroutine if parallelism is enabled.
	block blockWriter

	sizeEstimate struct {
		useMutex bool
		mu       sync.Mutex
		// numInflight is the number of index entries which are inflight and are yet to be added to the
		// index block.
		numInflight uint64
		// totalSize is the estimated size of the index block. This should match indexBlock.estimatedSize().
		totalSize uint64
		// numEntries is the total number of entries added to the index block.
		numEntries uint64
		// maxEstimatedSize stores the maximum result returned from indexBlockBuf.estimatedSize. It
		// ensures that values returned from subsequent calls to Writer.EstimatedSize never decrease.
		maxEstimatedSize uint64
		// emptySize is the size of an empty index block.
		emptySize uint64
	}
}

func (i *indexBlockBuf) size() uint64 {
	if i.sizeEstimate.useMutex {
		i.sizeEstimate.mu.Lock()
		defer i.sizeEstimate.mu.Unlock()
	}

	avgSize := float64(0)
	if i.sizeEstimate.numEntries > 0 {
		avgSize = float64(i.sizeEstimate.totalSize) / float64(i.sizeEstimate.numEntries)
	}

	total := i.sizeEstimate.totalSize + i.sizeEstimate.numInflight*uint64(avgSize)
	if total > i.sizeEstimate.maxEstimatedSize {
		i.sizeEstimate.maxEstimatedSize = total
	} else {
		total = i.sizeEstimate.maxEstimatedSize
	}

	if total == 0 {
		return emptyBlockSize
	}

	return total
}

func (i *indexBlockBuf) addInflight() {
	if i.sizeEstimate.useMutex {
		i.sizeEstimate.mu.Lock()
		defer i.sizeEstimate.mu.Unlock()
	}

	i.sizeEstimate.numInflight++
}

func (i *indexBlockBuf) indexEntryWritten() {
	size := i.block.estimatedSize()

	if i.sizeEstimate.useMutex {
		i.sizeEstimate.mu.Lock()
		defer i.sizeEstimate.mu.Unlock()
	}

	// When the Writer is closed, we write entries which aren't inflight. At that point
	// all inflight entries must already be written.
	if i.sizeEstimate.numInflight > 0 {
		i.sizeEstimate.numInflight--
	}

	i.sizeEstimate.numEntries++
	i.sizeEstimate.totalSize = uint64(size)
}

func (i *indexBlockBuf) add(key InternalKey, value []byte) {
	i.block.add(key, value)
	i.indexEntryWritten()
}

func (i *indexBlockBuf) finish() []byte {
	b := i.block.finish()
	i.clearEstimate()
	return b
}

func (i *indexBlockBuf) clearEstimate() {
	if i.sizeEstimate.useMutex {
		i.sizeEstimate.mu.Lock()
		defer i.sizeEstimate.mu.Unlock()
	}

	i.sizeEstimate.numEntries = 0
	i.sizeEstimate.numInflight = 0
	i.sizeEstimate.maxEstimatedSize = 0
	i.sizeEstimate.totalSize = 0
}

// sizeEstimate is used for sstable size estimation. sizeEstimate can be accessed by
// the Writer client, writeQueue, compressionQueue goroutines. Fields should only be
// read/updated through the functions defined on the *sizeEstimate type.
type sizeEstimate struct {
	// If we don't do block compression, block writes in parallel, then we don't need to take
	// the performance hit of synchronizing using this mutex.
	useMutex bool
	mu       sync.Mutex

	// maxEstimatedSize stores the maximum result returned from sizeEstimate.size. It ensures
	// that values returned from subsequent calls to Writer.EstimatedSize never decrease. We need
	// to do this, because the compressed size of the inflight blocks before compression is an
	// estimate, and the true compressed size of the inflight blocks might be lower.
	maxEstimatedSize uint64
	// totalSize is the total size of the data which we've written to disk. This will match
	// Writer.meta.Size.
	totalSize uint64
	// inflightSize is the uncompressed size of the inflight data blocks. This is computed as
	// an estimate.
	inflightSize uint64

	// size is the total compressed size of the finished data blocks.
	compressedSize uint64
	// uncompressedSize is total uncompressed size of the finished data blocks.
	uncompressedSize uint64
}

// newTotalSize is the new w.meta.Size. inflightSize is the uncompressed block size estimate which
// was previously added to sizeEstimate.inflightSize. writtenSize is the compressed size of the block
// which was written to disk.
func (s *sizeEstimate) dataBlockWritten(newTotalSize uint64, inflightSize int, writtenSize int) {
	if s.useMutex {
		s.mu.Lock()
		defer s.mu.Unlock()
	}

	// Update fields required which are used to compute the compression ratio.
	s.uncompressedSize += uint64(inflightSize)
	s.compressedSize += uint64(writtenSize)

	s.totalSize = newTotalSize
	s.inflightSize -= uint64(inflightSize)
}

// size is an estimated size of datablock data which has been written to disk.
func (s *sizeEstimate) size() uint64 {
	if s.useMutex {
		s.mu.Lock()
		defer s.mu.Unlock()
	}

	ratio := float64(1)
	if s.uncompressedSize > 0 {
		ratio = float64(s.compressedSize) / float64(s.uncompressedSize)
	}

	estimatedInflightSize := uint64(float64(s.inflightSize) * ratio)
	total := estimatedInflightSize + s.totalSize
	if total > s.maxEstimatedSize {
		s.maxEstimatedSize = total
	} else {
		total = s.maxEstimatedSize
	}
	return total
}

func (s *sizeEstimate) addInflightDataBlock(size int) {
	if s.useMutex {
		s.mu.Lock()
		defer s.mu.Unlock()
	}

	s.inflightSize += uint64(size)
}

var writeTaskPool = sync.Pool{
	New: func() interface{} {
		t := &writeTask{}
		t.compressionDone = make(chan bool, 1)
		return t
	},
}

type checksummer struct {
	checksumType ChecksumType
	xxHasher     *xxhash.Digest
}

func (c *checksummer) checksum(block []byte, blockType []byte) (checksum uint32) {
	// Calculate the checksum.
	switch c.checksumType {
	case ChecksumTypeCRC32c:
		checksum = crc.New(block).Update(blockType).Value()
	case ChecksumTypeXXHash64:
		if c.xxHasher == nil {
			c.xxHasher = xxhash.New()
		} else {
			c.xxHasher.Reset()
		}
		c.xxHasher.Write(block)
		c.xxHasher.Write(blockType)
		checksum = uint32(c.xxHasher.Sum64())
	default:
		panic(errors.Newf("unsupported checksum type: %d", c.checksumType))
	}
	return checksum
}

type blockBuf struct {
	// tmp is a scratch buffer, large enough to hold either footerLen bytes,
	// blockTrailerLen bytes, (5 * binary.MaxVarintLen64) bytes, and most
	// likely large enough for a block handle with properties.
	tmp [blockHandleLikelyMaxLen]byte
	// compressedBuf is the destination buffer for compression. It is re-used over the
	// lifetime of the blockBuf, avoiding the allocation of a temporary buffer for each block.
	compressedBuf []byte
	checksummer   checksummer
}

// A dataBlockBuf holds all the state required to compress and write a data block to disk.
// A dataBlockBuf begins its lifecycle owned by the Writer client goroutine. The Writer
// client goroutine adds keys to the sstable, writing directly into a dataBlockBuf's blockWriter
// until the block is full. Once a dataBlockBuf's block is full, the dataBlockBuf may be passed
// to other goroutines for compression and file I/O.
type dataBlockBuf struct {
	blockBuf
	dataBlock blockWriter

	// uncompressed is a reference to a byte slice which is owned by the dataBlockBuf. It is the
	// next byte slice to be compressed. The uncompressed byte slice will be backed by the
	// dataBlock.buf.
	uncompressed []byte
	// compressed is a reference to a byte slice which is owned by the dataBlockBuf. It is the
	// compressed byte slice which must be written to disk. The compressed byte slice may be
	// backed by the dataBlock.buf, or the dataBlockBuf.compressedBuf, depending on whether
	// we use the result of the compression.
	compressed []byte
}

var dataBlockBufPool = sync.Pool{
	New: func() interface{} {
		return &dataBlockBuf{}
	},
}

func newDataBlockBuf(restartInterval int, checksumType ChecksumType) *dataBlockBuf {
	d := dataBlockBufPool.Get().(*dataBlockBuf)
	d.dataBlock.restartInterval = restartInterval
	d.checksummer.checksumType = checksumType
	return d
}

func (d *dataBlockBuf) finish() {
	d.uncompressed = d.dataBlock.finish()
}

func (d *dataBlockBuf) compressAndChecksum(c Compression) {
	d.compressed = compressAndChecksum(d.uncompressed, c, &d.blockBuf)
}

type indexBlockAndBlockProperties struct {
	nEntries int
	// sep is the last key added to this block, for computing a separator later.
	sep        InternalKey
	properties []byte
	// block is the encoded block produced by blockWriter.finish.
	block []byte
}

// Set sets the value for the given key. The sequence number is set to
// 0. Intended for use to externally construct an sstable before ingestion into
// a DB.
//
// TODO(peter): untested
func (w *Writer) Set(key, value []byte) error {
	if w.err != nil {
		return w.err
	}
	return w.addPoint(base.MakeInternalKey(key, 0, InternalKeyKindSet), value)
}

// Delete deletes the value for the given key. The sequence number is set to
// 0. Intended for use to externally construct an sstable before ingestion into
// a DB.
//
// TODO(peter): untested
func (w *Writer) Delete(key []byte) error {
	if w.err != nil {
		return w.err
	}
	return w.addPoint(base.MakeInternalKey(key, 0, InternalKeyKindDelete), nil)
}

// DeleteRange deletes all of the keys (and values) in the range [start,end)
// (inclusive on start, exclusive on end). The sequence number is set to
// 0. Intended for use to externally construct an sstable before ingestion into
// a DB.
//
// TODO(peter): untested
func (w *Writer) DeleteRange(start, end []byte) error {
	if w.err != nil {
		return w.err
	}
	return w.addTombstone(base.MakeInternalKey(start, 0, InternalKeyKindRangeDelete), end)
}

// Merge adds an action to the DB that merges the value at key with the new
// value. The details of the merge are dependent upon the configured merge
// operator. The sequence number is set to 0. Intended for use to externally
// construct an sstable before ingestion into a DB.
//
// TODO(peter): untested
func (w *Writer) Merge(key, value []byte) error {
	if w.err != nil {
		return w.err
	}
	return w.addPoint(base.MakeInternalKey(key, 0, InternalKeyKindMerge), value)
}

// Add adds a key/value pair to the table being written. For a given Writer,
// the keys passed to Add must be in increasing order. The exception to this
// rule is range deletion tombstones. Range deletion tombstones need to be
// added ordered by their start key, but they can be added out of order from
// point entries. Additionally, range deletion tombstones must be fragmented
// (i.e. by keyspan.Fragmenter).
func (w *Writer) Add(key InternalKey, value []byte) error {
	if w.err != nil {
		return w.err
	}

	switch key.Kind() {
	case InternalKeyKindRangeDelete:
		return w.addTombstone(key, value)
	case base.InternalKeyKindRangeKeyDelete,
		base.InternalKeyKindRangeKeySet,
		base.InternalKeyKindRangeKeyUnset:
		w.err = errors.Errorf(
			"pebble: range keys must be added via one of the RangeKey* functions")
		return w.err
	}
	return w.addPoint(key, value)
}

func (w *Writer) addPoint(key InternalKey, value []byte) error {
	if !w.disableKeyOrderChecks && w.meta.LargestPoint.UserKey != nil {
		// TODO(peter): Manually inlined version of base.InternalCompare(). This is
		// 3.5% faster on BenchmarkWriter on go1.13. Remove if go1.14 or future
		// versions show this to not be a performance win.
		x := w.compare(w.meta.LargestPoint.UserKey, key.UserKey)
		if x > 0 || (x == 0 && w.meta.LargestPoint.Trailer < key.Trailer) {
			w.err = errors.Errorf("pebble: keys must be added in order: %s, %s",
				w.meta.LargestPoint.Pretty(w.formatKey), key.Pretty(w.formatKey))
			return w.err
		}
	}

	if err := w.maybeFlush(key, value); err != nil {
		return err
	}

	for i := range w.propCollectors {
		if err := w.propCollectors[i].Add(key, value); err != nil {
			w.err = err
			return err
		}
	}
	for i := range w.blockPropCollectors {
		if err := w.blockPropCollectors[i].Add(key, value); err != nil {
			w.err = err
			return err
		}
	}

	w.maybeAddToFilter(key.UserKey)
	w.dataBlockBuf.dataBlock.add(key, value)

	w.meta.updateSeqNum(key.SeqNum())
	// block.curKey contains the most recently added key to the block.
	w.meta.LargestPoint.UserKey = w.dataBlockBuf.dataBlock.curKey[:len(w.dataBlockBuf.dataBlock.curKey)-8]
	w.meta.LargestPoint.Trailer = key.Trailer
	if w.meta.SmallestPoint.UserKey == nil {
		// NB: we clone w.meta.LargestPoint rather than "key", even though they are
		// semantically identical, because we need to ensure that SmallestPoint.UserKey
		// is not nil. This is required by WriterMetadata.Smallest in order to
		// distinguish between an unset SmallestPoint and a zero-length one.
		// NB: We don't clone this off of some alloc-pool since it will outlive this
		// Writer as a field of the returned metadata that users like compaction.go
		// then hang on to, and would otherwise continue to alias that whole pool's
		// slice if we did so. So since we'll need to allocate it its own slice at
		// some point anyway, we may as well do so here.
		w.meta.SmallestPoint = w.meta.LargestPoint.Clone()
	}

	w.props.NumEntries++
	switch key.Kind() {
	case InternalKeyKindDelete:
		w.props.NumDeletions++
	case InternalKeyKindMerge:
		w.props.NumMergeOperands++
	}
	w.props.RawKeySize += uint64(key.Size())
	w.props.RawValueSize += uint64(len(value))
	return nil
}

func (w *Writer) addTombstone(key InternalKey, value []byte) error {
	if !w.disableKeyOrderChecks && !w.rangeDelV1Format && w.rangeDelBlock.nEntries > 0 {
		// Check that tombstones are being added in fragmented order. If the two
		// tombstones overlap, their start and end keys must be identical.
		prevKey := base.DecodeInternalKey(w.rangeDelBlock.curKey)
		switch c := w.compare(prevKey.UserKey, key.UserKey); {
		case c > 0:
			w.err = errors.Errorf("pebble: keys must be added in order: %s, %s",
				prevKey.Pretty(w.formatKey), key.Pretty(w.formatKey))
			return w.err
		case c == 0:
			prevValue := w.rangeDelBlock.curValue
			if w.compare(prevValue, value) != 0 {
				w.err = errors.Errorf("pebble: overlapping tombstones must be fragmented: %s vs %s",
					(keyspan.Span{Start: prevKey, End: prevValue}).Pretty(w.formatKey),
					(keyspan.Span{Start: key, End: value}).Pretty(w.formatKey))
				return w.err
			}
			if prevKey.SeqNum() <= key.SeqNum() {
				w.err = errors.Errorf("pebble: keys must be added in order: %s, %s",
					prevKey.Pretty(w.formatKey), key.Pretty(w.formatKey))
				return w.err
			}
		default:
			prevValue := w.rangeDelBlock.curValue
			if w.compare(prevValue, key.UserKey) > 0 {
				w.err = errors.Errorf("pebble: overlapping tombstones must be fragmented: %s vs %s",
					(keyspan.Span{Start: prevKey, End: prevValue}).Pretty(w.formatKey),
					(keyspan.Span{Start: key, End: value}).Pretty(w.formatKey))
				return w.err
			}
		}
	}

	if key.Trailer == InternalKeyRangeDeleteSentinel {
		w.err = errors.Errorf("pebble: cannot add range delete sentinel: %s", key.Pretty(w.formatKey))
		return w.err
	}

	for i := range w.propCollectors {
		if err := w.propCollectors[i].Add(key, value); err != nil {
			w.err = err
			return err
		}
	}

	w.meta.updateSeqNum(key.SeqNum())

	switch {
	case w.rangeDelV1Format:
		// Range tombstones are not fragmented in the v1 (i.e. RocksDB) range
		// deletion block format, so we need to track the largest range tombstone
		// end key as every range tombstone is added.
		//
		// Note that writing the v1 format is only supported for tests.
		if w.props.NumRangeDeletions == 0 {
			w.meta.SmallestRangeDel = key.Clone()
			w.meta.LargestRangeDel = base.MakeRangeDeleteSentinelKey(value).Clone()
		} else {
			if base.InternalCompare(w.compare, w.meta.SmallestRangeDel, key) > 0 {
				w.meta.SmallestRangeDel = key.Clone()
			}
			end := base.MakeRangeDeleteSentinelKey(value)
			if base.InternalCompare(w.compare, w.meta.LargestRangeDel, end) < 0 {
				w.meta.LargestRangeDel = end.Clone()
			}
		}

	default:
		// Range tombstones are fragmented in the v2 range deletion block format,
		// so the start key of the first range tombstone added will be the smallest
		// range tombstone key. The largest range tombstone key will be determined
		// in Writer.Close() as the end key of the last range tombstone added.
		if w.props.NumRangeDeletions == 0 {
			w.meta.SmallestRangeDel = key.Clone()
		}
	}

	w.props.NumEntries++
	w.props.NumDeletions++
	w.props.NumRangeDeletions++
	w.props.RawKeySize += uint64(key.Size())
	w.props.RawValueSize += uint64(len(value))
	w.rangeDelBlock.add(key, value)
	return nil
}

// RangeKeySet sets a range between start (inclusive) and end (exclusive) with
// the given suffix to the given value.
//
// Keys must be added to the table in increasing order of start key. Spans are
// not required to be fragmented.
func (w *Writer) RangeKeySet(start, end, suffix, value []byte) error {
	startKey := base.MakeInternalKey(start, 0, base.InternalKeyKindRangeKeySet)
	return w.addRangeKeySpan(startKey, end, suffix, value)
}

// RangeKeyUnset un-sets a range between start (inclusive) and end (exclusive)
// with the given suffix.
//
// Keys must be added to the table in increasing order of start key. Spans are
// not required to be fragmented.
func (w *Writer) RangeKeyUnset(start, end, suffix []byte) error {
	startKey := base.MakeInternalKey(start, 0, base.InternalKeyKindRangeKeyUnset)
	return w.addRangeKeySpan(startKey, end, suffix, nil /* value */)
}

// RangeKeyDelete deletes a range between start (inclusive) and end (exclusive).
//
// Keys must be added to the table in increasing order of start key. Spans are
// not required to be fragmented.
func (w *Writer) RangeKeyDelete(start, end []byte) error {
	startKey := base.MakeInternalKey(start, 0, base.InternalKeyKindRangeKeyDelete)
	return w.addRangeKeySpan(startKey, end, nil /* suffix */, nil /* value */)
}

// AddRangeKey adds a range key set, unset, or delete key/value pair to the
// table being written.
//
// Range keys must be supplied in strictly ascending order of start key (i.e.
// user key ascending, sequence number descending, and key type descending).
// Ranges added must also be supplied in fragmented span order - i.e. other than
// spans that are perfectly aligned (same start and end keys), spans may not
// overlap. Range keys may be added out of order relative to point keys and
// range deletions.
func (w *Writer) AddRangeKey(key InternalKey, value []byte) error {
	if w.err != nil {
		return w.err
	}
	return w.addRangeKey(key, value)
}

func (w *Writer) addRangeKeySpan(start base.InternalKey, end, suffix, value []byte) error {
	// NOTE: we take a copy of the range-key data and store in an internal buffer
	// for the the lifetime of the Writer. This removes the requirement on the
	// caller to avoid re-use of buffers until the Writer is closed.
	startUserKeyCopy := w.tempRangeKeyBuf(len(start.UserKey))
	copy(startUserKeyCopy, start.UserKey)
	startCopy := base.InternalKey{
		UserKey: startUserKeyCopy,
		Trailer: start.Trailer,
	}
	endCopy := w.tempRangeKeyBuf(len(end))
	copy(endCopy, end)

	span := keyspan.Span{Start: startCopy, End: endCopy}
	switch k := startCopy.Kind(); k {
	case base.InternalKeyKindRangeKeySet:
		svs := [1]rangekey.SuffixValue{{Suffix: suffix, Value: value}}
		buf := w.tempRangeKeyBuf(rangekey.EncodedSetSuffixValuesLen(svs[:]))
		rangekey.EncodeSetSuffixValues(buf, svs[:])
		span.Value = buf
	case base.InternalKeyKindRangeKeyUnset:
		suffixes := [][]byte{suffix}
		buf := w.tempRangeKeyBuf(rangekey.EncodedUnsetSuffixesLen(suffixes))
		rangekey.EncodeUnsetSuffixes(buf, suffixes)
		span.Value = buf
	case base.InternalKeyKindRangeKeyDelete:
		// No-op: delete spans are fully specified by a start and end key.
	default:
		panic(errors.Errorf("pebble: unexpected range key type: %s", k))
	}

	if w.fragmenter.Start() != nil && w.compare(w.fragmenter.Start(), span.Start.UserKey) > 0 {
		return errors.Errorf("pebble: spans must be added in order: %s > %s",
			w.formatKey(w.fragmenter.Start()), w.formatKey(span.Start.UserKey))
	}

	// Add this span to the fragmenter.
	w.fragmenter.Add(span)

	return nil
}

func (w *Writer) coalesceSpans(spans []keyspan.Span) {
	// This method is the emit function of the Fragmenter. As the Fragmenter is
	// guaranteed to receive spans in order of start key, an emitted slice of
	// spans from the Fragmenter will contain all of the fragments this Writer
	// will ever see. It is therefore safe to collect all of the received
	// fragments and emit a rangekey.CoalescedSpan.
	for _, span := range spans {
		if err := w.coalescer.Add(span); err != nil {
			w.err = errors.Newf("sstable: could not coalesce span: %s", err)
			return
		}
	}
	w.coalescer.Finish()
}

func (w *Writer) addCoalescedSpan(s rangekey.CoalescedSpan) {
	// This method is the emit function of the Coalescer. The incoming
	// CoalescedSpan is guaranteed to contain all fragments for this span in this
	// table. The fragments are collected by range key kind (i.e. RANGEKEYSET,
	// UNSET and DEL) and up to three key-value pairs are written to the table (up
	// to one pair for each of RANGEKEYSET, UNSET and DEL).
	var sets []rangekey.SuffixValue
	var unsets [][]byte
	for _, item := range s.Items {
		if item.Unset {
			unsets = append(unsets, item.Suffix)
		} else {
			sets = append(sets, rangekey.SuffixValue{Suffix: item.Suffix, Value: item.Value})
		}
	}

	// Write any RANGEKEYSETs.
	if len(sets) > 0 {
		key := base.MakeInternalKey(s.Start, s.LargestSeqNum, base.InternalKeyKindRangeKeySet)
		value := w.tempRangeKeyBuf(rangekey.EncodedSetValueLen(s.End, sets))
		rangekey.EncodeSetValue(value, s.End, sets)
		if err := w.addRangeKey(key, value); err != nil {
			w.err = errors.Newf("sstable: range key set: %s", err)
			return
		}
	}

	// Write any RANGEKEYUNSETs.
	if len(unsets) > 0 {
		key := base.MakeInternalKey(s.Start, s.LargestSeqNum, base.InternalKeyKindRangeKeyUnset)
		value := w.tempRangeKeyBuf(rangekey.EncodedUnsetValueLen(s.End, unsets))
		rangekey.EncodeUnsetValue(value, s.End, unsets)
		if err := w.addRangeKey(key, value); err != nil {
			w.err = errors.Newf("sstable: range key unset: %s", err)
			return
		}
	}

	// If the span contains a delete, add a RANGEKEYDEL.
	if s.Delete {
		k := base.MakeInternalKey(s.Start, s.LargestSeqNum, base.InternalKeyKindRangeKeyDelete)
		if err := w.addRangeKey(k, s.End); err != nil {
			w.err = errors.Newf("sstable: range key delete: %s", err)
			return
		}
	}
}

func (w *Writer) addRangeKey(key InternalKey, value []byte) error {
	if !w.disableKeyOrderChecks && w.rangeKeyBlock.nEntries > 0 {
		prevStartKey := base.DecodeInternalKey(w.rangeKeyBlock.curKey)
		prevEndKey, _, ok := rangekey.DecodeEndKey(prevStartKey.Kind(), w.rangeKeyBlock.curValue)
		if !ok {
			// We panic here as we should have previously decoded and validated this
			// key and value when it was first added to the range key block.
			panic(errors.Errorf("pebble: invalid end key for span: %s",
				(keyspan.Span{Start: prevStartKey, End: prevEndKey}).Pretty(w.formatKey)))
		}

		curStartKey := key
		curEndKey, _, ok := rangekey.DecodeEndKey(curStartKey.Kind(), value)
		if !ok {
			w.err = errors.Errorf("pebble: invalid end key for span: %s",
				(keyspan.Span{Start: curStartKey, End: curEndKey}).Pretty(w.formatKey))
			return w.err
		}

		// Start keys must be strictly increasing.
		if base.InternalCompare(w.compare, prevStartKey, curStartKey) >= 0 {
			w.err = errors.Errorf(
				"pebble: range keys starts must be added in strictly increasing order: %s, %s",
				prevStartKey.Pretty(w.formatKey), key.Pretty(w.formatKey))
			return w.err
		}

		// Start keys are strictly increasing. If the start user keys are equal, the
		// end keys must be equal (i.e. aligned spans).
		if w.compare(prevStartKey.UserKey, curStartKey.UserKey) == 0 {
			if w.compare(prevEndKey, curEndKey) != 0 {
				w.err = errors.Errorf("pebble: overlapping range keys must be fragmented: %s, %s",
					(keyspan.Span{Start: prevStartKey, End: prevEndKey}).Pretty(w.formatKey),
					(keyspan.Span{Start: curStartKey, End: curEndKey}).Pretty(w.formatKey))
				return w.err
			}
		} else if w.compare(prevEndKey, curStartKey.UserKey) > 0 {
			// If the start user keys are NOT equal, the spans must be disjoint (i.e.
			// no overlap).
			// NOTE: the inequality excludes zero, as we allow the end key of the
			// lower span be the same as the start key of the upper span, because
			// the range end key is considered an exclusive bound.
			w.err = errors.Errorf("pebble: overlapping range keys must be fragmented: %s, %s",
				(keyspan.Span{Start: prevStartKey, End: prevEndKey}).Pretty(w.formatKey),
				(keyspan.Span{Start: curStartKey, End: curEndKey}).Pretty(w.formatKey))
			return w.err
		}
	}

	// TODO(travers): Add an invariant-gated check to ensure that suffix-values
	// are sorted within coalesced spans.

	// Range-keys and point-keys are intended to live in "parallel" keyspaces.
	// However, we track a single seqnum in the table metadata that spans both of
	// these keyspaces.
	// TODO(travers): Consider tracking range key seqnums separately.
	w.meta.updateSeqNum(key.SeqNum())

	// Range tombstones are fragmented, so the start key of the first range key
	// added will be the smallest. The largest range key is determined in
	// Writer.Close() as the end key of the last range key added to the block.
	if w.props.NumRangeKeys() == 0 {
		w.meta.SmallestRangeKey = key.Clone()
	}

	// Update block properties.
	w.props.RawRangeKeyKeySize += uint64(key.Size())
	w.props.RawRangeKeyValueSize += uint64(len(value))
	switch key.Kind() {
	case base.InternalKeyKindRangeKeyDelete:
		w.props.NumRangeKeyDels++
	case base.InternalKeyKindRangeKeySet:
		w.props.NumRangeKeySets++
	case base.InternalKeyKindRangeKeyUnset:
		w.props.NumRangeKeyUnsets++
	default:
		panic(errors.Errorf("pebble: invalid range key type: %s", key.Kind()))
	}

	for i := range w.blockPropCollectors {
		if err := w.blockPropCollectors[i].Add(key, value); err != nil {
			return err
		}
	}

	// Add the key to the block.
	w.rangeKeyBlock.add(key, value)
	return nil
}

// tempRangeKeyBuf returns a slice of length n from the Writer's rkBuf byte
// slice. Any byte written to the returned slice is retained for the lifetime of
// the Writer.
func (w *Writer) tempRangeKeyBuf(n int) []byte {
	if cap(w.rkBuf)-len(w.rkBuf) < n {
		size := len(w.rkBuf) + 2*n
		if size < 2*cap(w.rkBuf) {
			size = 2 * cap(w.rkBuf)
		}
		buf := make([]byte, len(w.rkBuf), size)
		copy(buf, w.rkBuf)
		w.rkBuf = buf
	}
	b := w.rkBuf[len(w.rkBuf) : len(w.rkBuf)+n]
	w.rkBuf = w.rkBuf[:len(w.rkBuf)+n]
	return b
}

func (w *Writer) maybeAddToFilter(key []byte) {
	if w.filter != nil {
		if w.split != nil {
			prefix := key[:w.split(key)]
			w.filter.addKey(prefix)
		} else {
			w.filter.addKey(key)
		}
	}
}

func (w *Writer) flush(key InternalKey) error {
	estimatedUncompressedSize := w.dataBlockBuf.dataBlock.estimatedSize()
	w.coordination.sizeEstimate.addInflightDataBlock(estimatedUncompressedSize)

	w.dataBlockBuf.finish()
	w.dataBlockBuf.compressAndChecksum(w.compression)

	var err error
	writeTask := writeTaskPool.Get().(*writeTask)
	// We're setting compressionDone to indicate that compression of this block
	// has already been completed.
	writeTask.compressionDone <- true
	writeTask.buf = w.dataBlockBuf
	writeTask.indexSepKey = key
	writeTask.inflightSize = estimatedUncompressedSize

	// The writeTask corresponds to an unwritten index entry.
	w.indexBlock.addInflight()

	w.dataBlockBuf = nil
	err = w.coordination.writeQueue.addSync(writeTask)
	w.dataBlockBuf = newDataBlockBuf(w.restartInterval, w.checksumType)

	return err
}

func (w *Writer) maybeFlush(key InternalKey, value []byte) error {
	if !shouldFlush(key, value, &w.dataBlockBuf.dataBlock, w.blockSize, w.blockSizeThreshold) {
		return nil
	}

	err := w.flush(key)

	if err != nil {
		w.err = err
		return err
	}

	return nil
}

// The BlockHandleWithProperties returned by this method must be encoded
// before any future use of the Writer.blockPropsEncoder, since the properties
// slice will get reused by the blockPropsEncoder.
func (w *Writer) maybeAddBlockPropertiesToBlockHandle(
	bh BlockHandle,
) (BlockHandleWithProperties, error) {
	if len(w.blockPropCollectors) == 0 {
		return BlockHandleWithProperties{BlockHandle: bh}, nil
	}
	var err error
	w.blockPropsEncoder.resetProps()
	for i := range w.blockPropCollectors {
		scratch := w.blockPropsEncoder.getScratchForProp()
		if scratch, err = w.blockPropCollectors[i].FinishDataBlock(scratch); err != nil {
			return BlockHandleWithProperties{}, err
		}
		if len(scratch) > 0 {
			w.blockPropsEncoder.addProp(shortID(i), scratch)
		}
	}
	return BlockHandleWithProperties{BlockHandle: bh, Props: w.blockPropsEncoder.unsafeProps()}, nil
}

// addIndexEntry adds an index entry for the specified key and block handle.
func (w *Writer) addIndexEntry(prevKey, key InternalKey, bhp BlockHandleWithProperties, tmp []byte) error {
	if bhp.Length == 0 {
		// A valid blockHandle must be non-zero.
		// In particular, it must have a non-zero length.
		return nil
	}

	// Make a rough guess that we want key-sized scratch to compute the separator.
	if cap(w.sepScratch) < key.Size() {
		w.sepScratch = make([]byte, 0, key.Size()*2)
	}

	var sep InternalKey
	if key.UserKey == nil && key.Trailer == 0 {
		sep = prevKey.Successor(w.compare, w.successor, w.sepScratch[:0])
	} else {
		sep = prevKey.Separator(w.compare, w.separator, w.sepScratch[:0], key)
	}
	encoded := encodeBlockHandleWithProperties(tmp, bhp)

	if supportsTwoLevelIndex(w.tableFormat) &&
		shouldFlush(sep, encoded, &w.indexBlock.block, w.indexBlockSize, w.indexBlockSizeThreshold) {
		if cap(w.indexPartitions) == 0 {
			w.indexPartitions = make([]indexBlockAndBlockProperties, 0, 32)
		}
		// Enable two level indexes if there is more than one index block.
		w.twoLevelIndex = true
		if err := w.finishIndexBlock(); err != nil {
			return err
		}
	}

	for i := range w.blockPropCollectors {
		w.blockPropCollectors[i].AddPrevDataBlockToIndexBlock()
	}
	w.indexBlock.add(sep, encoded)
	return nil
}

func shouldFlush(
	key InternalKey, value []byte, block *blockWriter, blockSize, sizeThreshold int,
) bool {
	if block.nEntries == 0 {
		return false
	}

	size := block.estimatedSize()
	if size >= blockSize {
		return true
	}

	// The block is currently smaller than the target size.
	if size <= sizeThreshold {
		// The block is smaller than the threshold size at which we'll consider
		// flushing it.
		return false
	}

	newSize := size + key.Size() + len(value)
	if block.nEntries%block.restartInterval == 0 {
		newSize += 4
	}
	newSize += 4                              // varint for shared prefix length
	newSize += uvarintLen(uint32(key.Size())) // varint for unshared key bytes
	newSize += uvarintLen(uint32(len(value))) // varint for value size
	// Flush if the block plus the new entry is larger than the target size.
	return newSize > blockSize
}

const keyAllocSize = 256 << 10

func cloneKeyWithBuf(k InternalKey, buf []byte) ([]byte, InternalKey) {
	if len(k.UserKey) == 0 {
		return buf, k
	}
	if len(buf) < len(k.UserKey) {
		buf = make([]byte, len(k.UserKey)+keyAllocSize)
	}
	n := copy(buf, k.UserKey)
	return buf[n:], InternalKey{UserKey: buf[:n:n], Trailer: k.Trailer}
}

// finishIndexBlock finishes the current index block and adds it to the top
// level index block. This is only used when two level indexes are enabled.
func (w *Writer) finishIndexBlock() error {
	w.blockPropsEncoder.resetProps()
	for i := range w.blockPropCollectors {
		scratch := w.blockPropsEncoder.getScratchForProp()
		var err error
		if scratch, err = w.blockPropCollectors[i].FinishIndexBlock(scratch); err != nil {
			return err
		}
		if len(scratch) > 0 {
			w.blockPropsEncoder.addProp(shortID(i), scratch)
		}
	}
	part := indexBlockAndBlockProperties{
		nEntries: w.indexBlock.block.nEntries, properties: w.blockPropsEncoder.props(),
	}
	w.indexSepAlloc, part.sep = cloneKeyWithBuf(
		base.DecodeInternalKey(w.indexBlock.block.curKey), w.indexSepAlloc,
	)
	bk := w.indexBlock.finish()
	if len(w.indexBlockAlloc) < len(bk) {
		// Allocate enough bytes for approximately 16 index blocks.
		w.indexBlockAlloc = make([]byte, len(bk)*16)
	}
	n := copy(w.indexBlockAlloc, bk)
	part.block = w.indexBlockAlloc[:n:n]
	w.indexBlockAlloc = w.indexBlockAlloc[n:]
	w.indexPartitions = append(w.indexPartitions, part)
	return nil
}

func (w *Writer) writeTwoLevelIndex() (BlockHandle, error) {
	// Add the final unfinished index.
	if err := w.finishIndexBlock(); err != nil {
		return BlockHandle{}, err
	}

	for i := range w.indexPartitions {
		b := &w.indexPartitions[i]
		w.props.NumDataBlocks += uint64(b.nEntries)

		data := b.block
		w.props.IndexSize += uint64(len(data))
		bh, err := w.writeBlock(data, w.compression, &w.blockBuf)
		if err != nil {
			return BlockHandle{}, err
		}
		bhp := BlockHandleWithProperties{
			BlockHandle: bh,
			Props:       b.properties,
		}
		encoded := encodeBlockHandleWithProperties(w.blockBuf.tmp[:], bhp)
		w.topLevelIndexBlock.add(b.sep, encoded)
	}

	// NB: RocksDB includes the block trailer length in the index size
	// property, though it doesn't include the trailer in the top level
	// index size property.
	w.props.IndexPartitions = uint64(len(w.indexPartitions))
	w.props.TopLevelIndexSize = uint64(w.topLevelIndexBlock.estimatedSize())
	w.props.IndexSize += w.props.TopLevelIndexSize + blockTrailerLen

	return w.writeBlock(w.topLevelIndexBlock.finish(), w.compression, &w.blockBuf)
}

func compressAndChecksum(b []byte, compression Compression, blockBuf *blockBuf) []byte {
	// Compress the buffer, discarding the result if the improvement isn't at
	// least 12.5%.
	blockType, compressed := compressBlock(compression, b, blockBuf.compressedBuf)
	if blockType != noCompressionBlockType && cap(compressed) > cap(blockBuf.compressedBuf) {
		blockBuf.compressedBuf = compressed[:cap(compressed)]
	}
	if len(compressed) < len(b)-len(b)/8 {
		b = compressed
	} else {
		blockType = noCompressionBlockType
	}

	blockBuf.tmp[0] = byte(blockType)

	// Calculate the checksum.
	checksum := blockBuf.checksummer.checksum(b, blockBuf.tmp[:1])
	binary.LittleEndian.PutUint32(blockBuf.tmp[1:5], checksum)
	return b
}

func (w *Writer) writeCompressedBlock(
	block []byte, blockTrailerBuf []byte,
) (BlockHandle, error) {
	bh := BlockHandle{Offset: w.meta.Size, Length: uint64(len(block))}

	if w.cacheID != 0 && w.fileNum != 0 {
		// Remove the block being written from the cache. This provides defense in
		// depth against bugs which cause cache collisions.
		//
		// TODO(peter): Alternatively, we could add the uncompressed value to the
		// cache.
		w.cache.Delete(w.cacheID, w.fileNum, bh.Offset)
	}

	// Write the bytes to the file.
	n, err := w.writer.Write(block)
	if err != nil {
		return BlockHandle{}, err
	}
	w.meta.Size += uint64(n)
	n, err = w.writer.Write(blockTrailerBuf[:blockTrailerLen])
	if err != nil {
		return BlockHandle{}, err
	}
	w.meta.Size += uint64(n)

	return bh, nil
}

func (w *Writer) writeBlock(
	b []byte, compression Compression, blockBuf *blockBuf,
) (BlockHandle, error) {
	b = compressAndChecksum(b, compression, blockBuf)
	return w.writeCompressedBlock(b, blockBuf.tmp[:])
}

// assertFormatCompatibility ensures that the features present on the table are
// compatible with the table format version.
func (w *Writer) assertFormatCompatibility() error {
	// PebbleDBv1: block properties.
	if len(w.blockPropCollectors) > 0 && w.tableFormat < TableFormatPebblev1 {
		return errors.Newf(
			"table format version %s is less than the minimum required version %s for block properties",
			w.tableFormat, TableFormatPebblev1,
		)
	}

	// PebbleDBv2: range keys.
	if w.props.NumRangeKeys() > 0 && w.tableFormat < TableFormatPebblev2 {
		return errors.Newf(
			"table format version %s is less than the minimum required version %s for range keys",
			w.tableFormat, TableFormatPebblev2,
		)
	}

	return nil
}

// Close finishes writing the table and closes the underlying file that the
// table was written to.
func (w *Writer) Close() (err error) {
	defer func() {
		if w.syncer == nil {
			return
		}
		err1 := w.syncer.Close()
		if err == nil {
			err = err1
		}
		w.syncer = nil
	}()

	// finish must be called before we check for an error, because finish will
	// block until every single task added to the writeQueue has been processed,
	// and an error could be encountered while any of those tasks are processed.
	if err = w.coordination.writeQueue.finish(); err != nil {
		w.err = err
	}

	if w.err != nil {
		return w.err
	}

	// Finish the last data block, or force an empty data block if there
	// aren't any data blocks at all.
	if w.dataBlockBuf.dataBlock.nEntries > 0 || w.indexBlock.block.nEntries == 0 {
		bh, err := w.writeBlock(w.dataBlockBuf.dataBlock.finish(), w.compression, &w.dataBlockBuf.blockBuf)
		if err != nil {
			w.err = err
			return w.err
		}
		var bhp BlockHandleWithProperties
		if bhp, err = w.maybeAddBlockPropertiesToBlockHandle(bh); err != nil {
			w.err = err
			return err
		}
		prevKey := base.DecodeInternalKey(w.dataBlockBuf.dataBlock.curKey)
		if err = w.addIndexEntry(prevKey, InternalKey{}, bhp, w.dataBlockBuf.tmp[:]); err != nil {
			w.err = err
			return err
		}
	}
	w.props.DataSize = w.meta.Size

	// Write the filter block.
	var metaindex rawBlockWriter
	metaindex.restartInterval = 1
	if w.filter != nil {
		b, err := w.filter.finish()
		if err != nil {
			w.err = err
			return w.err
		}
		bh, err := w.writeBlock(b, NoCompression, &w.blockBuf)
		if err != nil {
			w.err = err
			return w.err
		}
		n := encodeBlockHandle(w.blockBuf.tmp[:], bh)
		metaindex.add(InternalKey{UserKey: []byte(w.filter.metaName())}, w.blockBuf.tmp[:n])
		w.props.FilterPolicyName = w.filter.policyName()
		w.props.FilterSize = bh.Length
	}

	var indexBH BlockHandle
	if w.twoLevelIndex {
		w.props.IndexType = twoLevelIndex
		// Write the two level index block.
		indexBH, err = w.writeTwoLevelIndex()
		if err != nil {
			w.err = err
			return w.err
		}
	} else {
		w.props.IndexType = binarySearchIndex
		// NB: RocksDB includes the block trailer length in the index size
		// property, though it doesn't include the trailer in the filter size
		// property.
		w.props.IndexSize = uint64(w.indexBlock.size()) + blockTrailerLen
		w.props.NumDataBlocks = uint64(w.indexBlock.block.nEntries)

		// Write the single level index block.
		indexBH, err = w.writeBlock(w.indexBlock.finish(), w.compression, &w.blockBuf)
		if err != nil {
			w.err = err
			return w.err
		}
	}

	// Write the range-del block. The block handle must added to the meta index block
	// after the properties block has been written. This is because the entries in the
	// metaindex block must be sorted by key.
	var rangeDelBH BlockHandle
	if w.props.NumRangeDeletions > 0 {
		if !w.rangeDelV1Format {
			// Because the range tombstones are fragmented in the v2 format, the end
			// key of the last added range tombstone will be the largest range
			// tombstone key. Note that we need to make this into a range deletion
			// sentinel because sstable boundaries are inclusive while the end key of
			// a range deletion tombstone is exclusive. A Clone() is necessary as
			// rangeDelBlock.curValue is the same slice that will get passed
			// into w.writer, and some implementations of vfs.File mutate the
			// slice passed into Write(). Also, w.meta will often outlive the
			// blockWriter, and so cloning curValue allows the rangeDelBlock's
			// internal buffer to get gc'd.
			w.meta.LargestRangeDel = base.MakeRangeDeleteSentinelKey(w.rangeDelBlock.curValue).Clone()
		}
		rangeDelBH, err = w.writeBlock(w.rangeDelBlock.finish(), NoCompression, &w.blockBuf)
		if err != nil {
			w.err = err
			return w.err
		}
	}

	// Write the range-key block, flushing any remaining spans from the
	// fragmenter first.
	w.fragmenter.Finish()

	var rangeKeyBH BlockHandle
	if w.props.NumRangeKeys() > 0 {
		key := base.DecodeInternalKey(w.rangeKeyBlock.curKey)
		kind := key.Kind()
		endKey, _, ok := rangekey.DecodeEndKey(kind, w.rangeKeyBlock.curValue)
		if !ok {
			w.err = errors.Newf("invalid end key: %s", w.rangeKeyBlock.curValue)
			return w.err
		}
		w.meta.LargestRangeKey = base.MakeInternalKey(endKey, base.InternalKeySeqNumMax, key.Kind()).Clone()
		// TODO(travers): The lack of compression on the range key block matches the
		// lack of compression on the range-del block. Revisit whether we want to
		// enable compression on this block.
		rangeKeyBH, err = w.writeBlock(w.rangeKeyBlock.finish(), NoCompression, &w.blockBuf)
		if err != nil {
			w.err = err
			return w.err
		}
	}

	// Add the range key block handle to the metaindex block. Note that we add the
	// block handle to the metaindex block before the other meta blocks as the
	// metaindex block entries must be sorted, and the range key block name sorts
	// before the other block names.
	if w.props.NumRangeKeys() > 0 {
		n := encodeBlockHandle(w.blockBuf.tmp[:], rangeKeyBH)
		metaindex.add(InternalKey{UserKey: []byte(metaRangeKeyName)}, w.blockBuf.tmp[:n])
	}

	{
		userProps := make(map[string]string)
		for i := range w.propCollectors {
			if err := w.propCollectors[i].Finish(userProps); err != nil {
				w.err = err
				return err
			}
		}
		for i := range w.blockPropCollectors {
			scratch := w.blockPropsEncoder.getScratchForProp()
			// Place the shortID in the first byte.
			scratch = append(scratch, byte(i))
			buf, err :=
				w.blockPropCollectors[i].FinishTable(scratch)
			if err != nil {
				w.err = err
				return err
			}
			var prop string
			if len(buf) > 0 {
				prop = string(buf)
			}
			// NB: The property is populated in the map even if it is the
			// empty string, since the presence in the map is what indicates
			// that the block property collector was used when writing.
			userProps[w.blockPropCollectors[i].Name()] = prop
		}
		if len(userProps) > 0 {
			w.props.UserProperties = userProps
		}

		// Write the properties block.
		var raw rawBlockWriter
		// The restart interval is set to infinity because the properties block
		// is always read sequentially and cached in a heap located object. This
		// reduces table size without a significant impact on performance.
		raw.restartInterval = propertiesBlockRestartInterval
		w.props.CompressionOptions = rocksDBCompressionOptions
		w.props.save(&raw)
		bh, err := w.writeBlock(raw.finish(), NoCompression, &w.blockBuf)
		if err != nil {
			w.err = err
			return w.err
		}
		n := encodeBlockHandle(w.blockBuf.tmp[:], bh)
		metaindex.add(InternalKey{UserKey: []byte(metaPropertiesName)}, w.blockBuf.tmp[:n])
	}

	// Add the range deletion block handle to the metaindex block.
	if w.props.NumRangeDeletions > 0 {
		n := encodeBlockHandle(w.blockBuf.tmp[:], rangeDelBH)
		// The v2 range-del block encoding is backwards compatible with the v1
		// encoding. We add meta-index entries for both the old name and the new
		// name so that old code can continue to find the range-del block and new
		// code knows that the range tombstones in the block are fragmented and
		// sorted.
		metaindex.add(InternalKey{UserKey: []byte(metaRangeDelName)}, w.blockBuf.tmp[:n])
		if !w.rangeDelV1Format {
			metaindex.add(InternalKey{UserKey: []byte(metaRangeDelV2Name)}, w.blockBuf.tmp[:n])
		}
	}

	// Write the metaindex block. It might be an empty block, if the filter
	// policy is nil. NoCompression is specified because a) RocksDB never
	// compresses the meta-index block and b) RocksDB has some code paths which
	// expect the meta-index block to not be compressed.
	metaindexBH, err := w.writeBlock(metaindex.blockWriter.finish(), NoCompression, &w.blockBuf)
	if err != nil {
		w.err = err
		return w.err
	}

	// Write the table footer.
	footer := footer{
		format:      w.tableFormat,
		checksum:    w.blockBuf.checksummer.checksumType,
		metaindexBH: metaindexBH,
		indexBH:     indexBH,
	}
	var n int
	if n, err = w.writer.Write(footer.encode(w.blockBuf.tmp[:])); err != nil {
		w.err = err
		return w.err
	}
	w.meta.Size += uint64(n)
	w.meta.Properties = w.props

	// Flush the buffer.
	if w.bufWriter != nil {
		if err := w.bufWriter.Flush(); err != nil {
			w.err = err
			return err
		}
	}

	// Check that the features present in the table are compatible with the format
	// configured for the table.
	if err = w.assertFormatCompatibility(); err != nil {
		w.err = err
		return w.err
	}

	if err := w.syncer.Sync(); err != nil {
		w.err = err
		return err
	}

	// Make any future calls to Set or Close return an error.
	w.err = errWriterClosed
	return nil
}

// EstimatedSize returns the estimated size of the sstable being written if a
// called to Finish() was made without adding additional keys.
func (w *Writer) EstimatedSize() uint64 {
	return w.coordination.sizeEstimate.size() +
		uint64(w.dataBlockBuf.dataBlock.estimatedSize()) + w.indexBlock.size()
}

// Metadata returns the metadata for the finished sstable. Only valid to call
// after the sstable has been finished.
func (w *Writer) Metadata() (*WriterMetadata, error) {
	if w.syncer != nil {
		return nil, errors.New("pebble: writer is not closed")
	}
	return &w.meta, nil
}

// WriterOption provide an interface to do work on Writer while it is being
// opened.
type WriterOption interface {
	// writerAPply is called on the writer during opening in order to set
	// internal parameters.
	writerApply(*Writer)
}

// PreviousPointKeyOpt is a WriterOption that provides access to the last
// point key written to the writer while building a sstable.
type PreviousPointKeyOpt struct {
	w *Writer
}

// UnsafeKey returns the last point key written to the writer to which this
// option was passed during creation. The returned key points directly into
// a buffer belonging the Writer. The value's lifetime ends the next time a
// point key is added to the Writer.
func (o PreviousPointKeyOpt) UnsafeKey() base.InternalKey {
	if o.w == nil {
		return base.InvalidInternalKey
	}
	return o.w.meta.LargestPoint
}

func (o *PreviousPointKeyOpt) writerApply(w *Writer) {
	o.w = w
}

// internalTableOpt is a WriterOption that sets properties for sstables being
// created by the db itself (i.e. through flushes and compactions), as opposed
// to those meant for ingestion.
type internalTableOpt struct{}

func (i internalTableOpt) writerApply(w *Writer) {
	// Set the external sst version to 0. This is what RocksDB expects for
	// db-internal sstables; otherwise, it could apply a global sequence number.
	w.props.ExternalFormatVersion = 0
}

// NewWriter returns a new table writer for the file. Closing the writer will
// close the file.
func NewWriter(f writeCloseSyncer, o WriterOptions, extraOpts ...WriterOption) *Writer {
	o = o.ensureDefaults()
	w := &Writer{
		syncer: f,
		meta: WriterMetadata{
			SmallestSeqNum: math.MaxUint64,
		},
		blockSize:               o.BlockSize,
		blockSizeThreshold:      (o.BlockSize*o.BlockSizeThreshold + 99) / 100,
		indexBlockSize:          o.IndexBlockSize,
		indexBlockSizeThreshold: (o.IndexBlockSize*o.BlockSizeThreshold + 99) / 100,
		compare:                 o.Comparer.Compare,
		split:                   o.Comparer.Split,
		formatKey:               o.Comparer.FormatKey,
		compression:             o.Compression,
		separator:               o.Comparer.Separator,
		successor:               o.Comparer.Successor,
		tableFormat:             o.TableFormat,
		cache:                   o.Cache,
		restartInterval:         o.BlockRestartInterval,
		checksumType:            o.Checksum,
		indexBlock: indexBlockBuf{
			block: blockWriter{
				restartInterval: 1,
			},
		},
		rangeDelBlock: blockWriter{
			restartInterval: 1,
		},
		rangeKeyBlock: blockWriter{
			restartInterval: 1,
		},
		topLevelIndexBlock: blockWriter{
			restartInterval: 1,
		},
		fragmenter: keyspan.Fragmenter{
			Cmp:    o.Comparer.Compare,
			Format: o.Comparer.FormatKey,
		},
		coalescer: rangekey.Coalescer{},
	}

	w.dataBlockBuf = newDataBlockBuf(w.restartInterval, w.checksumType)

	w.blockBuf = blockBuf{
		checksummer: checksummer{checksumType: o.Checksum},
	}

	// We only need to use a mutex when we decide to truly write blocks in parallel.
	w.coordination.sizeEstimate.useMutex = false

	// We're creating the writeQueue with a size of 0, because we won't be using
	// the async queue until parallelism is enabled, and we do all block writes
	// through writeQueue.addSync.
	w.coordination.writeQueue = newWriteQueue(0, w)

	if f == nil {
		w.err = errors.New("pebble: nil file")
		return w
	}

	// Note that WriterOptions are applied in two places; the ones with a
	// preApply() method are applied here, and the rest are applied after
	// default properties are set.
	type preApply interface{ preApply() }
	for _, opt := range extraOpts {
		if _, ok := opt.(preApply); ok {
			opt.writerApply(w)
		}
	}

	w.props.PrefixExtractorName = "nullptr"
	if o.FilterPolicy != nil {
		switch o.FilterType {
		case TableFilter:
			w.filter = newTableFilterWriter(o.FilterPolicy)
			if w.split != nil {
				w.props.PrefixExtractorName = o.Comparer.Name
				w.props.PrefixFiltering = true
			} else {
				w.props.WholeKeyFiltering = true
			}
		default:
			panic(fmt.Sprintf("unknown filter type: %v", o.FilterType))
		}
	}

	w.props.ColumnFamilyID = math.MaxInt32
	w.props.ComparerName = o.Comparer.Name
	w.props.CompressionName = o.Compression.String()
	w.props.MergerName = o.MergerName
	w.props.PropertyCollectorNames = "[]"
	w.props.ExternalFormatVersion = rocksDBExternalFormatVersion

	if len(o.TablePropertyCollectors) > 0 || len(o.BlockPropertyCollectors) > 0 {
		var buf bytes.Buffer
		buf.WriteString("[")
		if len(o.TablePropertyCollectors) > 0 {
			w.propCollectors = make([]TablePropertyCollector, len(o.TablePropertyCollectors))
			for i := range o.TablePropertyCollectors {
				w.propCollectors[i] = o.TablePropertyCollectors[i]()
				if i > 0 {
					buf.WriteString(",")
				}
				buf.WriteString(w.propCollectors[i].Name())
			}
		}
		if len(o.BlockPropertyCollectors) > 0 {
			// shortID is a uint8, so we cannot exceed that number of block
			// property collectors.
			if len(o.BlockPropertyCollectors) > math.MaxUint8 {
				w.err = errors.New("pebble: too many block property collectors")
				return w
			}
			// The shortID assigned to a collector is the same as its index in
			// this slice.
			w.blockPropCollectors = make([]BlockPropertyCollector, len(o.BlockPropertyCollectors))
			for i := range o.BlockPropertyCollectors {
				w.blockPropCollectors[i] = o.BlockPropertyCollectors[i]()
				if i > 0 || len(o.TablePropertyCollectors) > 0 {
					buf.WriteString(",")
				}
				buf.WriteString(w.blockPropCollectors[i].Name())
			}
		}
		buf.WriteString("]")
		w.props.PropertyCollectorNames = buf.String()
	}

	// Apply the remaining WriterOptions that do not have a preApply() method.
	for _, opt := range extraOpts {
		if _, ok := opt.(preApply); !ok {
			opt.writerApply(w)
		}
	}

	// Initialize the range key fragmenter and coalescer.
	w.fragmenter.Emit = w.coalesceSpans
	w.coalescer.Init(w.compare, w.formatKey, base.InternalKeySeqNumMax, w.addCoalescedSpan)

	// If f does not have a Flush method, do our own buffering.
	if _, ok := f.(flusher); ok {
		w.writer = f
	} else {
		w.bufWriter = bufio.NewWriter(f)
		w.writer = w.bufWriter
	}
	return w
}

func init() {
	private.SSTableWriterDisableKeyOrderChecks = func(i interface{}) {
		w := i.(*Writer)
		w.disableKeyOrderChecks = true
	}
	private.SSTableInternalTableOpt = internalTableOpt{}
}