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 (
	"bytes"
	"encoding/binary"
	"fmt"
	"math"
	"runtime"
	"sort"
	"sync"

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

// encodedBHPEstimatedSize estimates the size of the encoded BlockHandleWithProperties.
// It would also be nice to account for the length of the data block properties here,
// but isn't necessary since this is an estimate.
const encodedBHPEstimatedSize = binary.MaxVarintLen64 * 2

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

// WriterMetadata holds info about a finished sstable.
type WriterMetadata struct {
	Size          uint64
	SmallestPoint InternalKey
	// LargestPoint, LargestRangeKey, LargestRangeDel should not be accessed
	// before Writer.Close is called, because they may only be set on
	// Writer.Close.
	LargestPoint     InternalKey
	SmallestRangeDel InternalKey
	LargestRangeDel  InternalKey
	SmallestRangeKey InternalKey
	LargestRangeKey  InternalKey
	HasPointKeys     bool
	HasRangeDelKeys  bool
	HasRangeKeys     bool
	SmallestSeqNum   uint64
	LargestSeqNum    uint64
	Properties       Properties
}

// SetSmallestPointKey sets the smallest point key to the given key.
// NB: this method set the "absolute" smallest point key. Any existing key is
// overridden.
func (m *WriterMetadata) SetSmallestPointKey(k InternalKey) {
	m.SmallestPoint = k
	m.HasPointKeys = true
}

// SetSmallestRangeDelKey sets the smallest rangedel key to the given key.
// NB: this method set the "absolute" smallest rangedel key. Any existing key is
// overridden.
func (m *WriterMetadata) SetSmallestRangeDelKey(k InternalKey) {
	m.SmallestRangeDel = k
	m.HasRangeDelKeys = true
}

// SetSmallestRangeKey sets the smallest range key to the given key.
// NB: this method set the "absolute" smallest range key. Any existing key is
// overridden.
func (m *WriterMetadata) SetSmallestRangeKey(k InternalKey) {
	m.SmallestRangeKey = k
	m.HasRangeKeys = true
}

// SetLargestPointKey sets the largest point key to the given key.
// NB: this method set the "absolute" largest point key. Any existing key is
// overridden.
func (m *WriterMetadata) SetLargestPointKey(k InternalKey) {
	m.LargestPoint = k
	m.HasPointKeys = true
}

// SetLargestRangeDelKey sets the largest rangedel key to the given key.
// NB: this method set the "absolute" largest rangedel key. Any existing key is
// overridden.
func (m *WriterMetadata) SetLargestRangeDelKey(k InternalKey) {
	m.LargestRangeDel = k
	m.HasRangeDelKeys = true
}

// SetLargestRangeKey sets the largest range key to the given key.
// NB: this method set the "absolute" largest range key. Any existing key is
// overridden.
func (m *WriterMetadata) SetLargestRangeKey(k InternalKey) {
	m.LargestRangeKey = k
	m.HasRangeKeys = true
}

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

// Writer is a table writer.
type Writer struct {
	writable objstorage.Writable
	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.DiskFileNum
	// 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
	isStrictObsolete        bool
	writingToLowestLevel    bool
	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
	obsoleteCollector   obsoleteKeyBlockPropertyCollector
	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

	// 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 separator slices stored
	// in indexPartitions. These live until the index finishes.
	indexSepAlloc bytealloc.A

	// To allow potentially overlapping (i.e. un-fragmented) range keys spans to
	// be added to the Writer, a keyspan.Fragmenter is 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
	rangeKeyEncoder   rangekey.Encoder
	rangeKeysBySuffix keyspan.KeysBySuffix
	rangeKeySpan      keyspan.Span
	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 coordinationState

	// Information (other than the byte slice) about the last point key, to
	// avoid extracting it again.
	lastPointKeyInfo pointKeyInfo

	// For value blocks.
	shortAttributeExtractor   base.ShortAttributeExtractor
	requiredInPlaceValueBound UserKeyPrefixBound
	valueBlockWriter          *valueBlockWriter
}

type pointKeyInfo struct {
	trailer uint64
	// Only computed when w.valueBlockWriter is not nil.
	userKeyLen int
	// prefixLen uses w.split, if not nil. Only computed when w.valueBlockWriter
	// is not nil.
	prefixLen int
	// True iff the point was marked obsolete.
	isObsolete bool
}

type coordinationState struct {
	parallelismEnabled bool

	// 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 dataBlockEstimates
}

func (c *coordinationState) init(parallelismEnabled bool, writer *Writer) {
	c.parallelismEnabled = parallelismEnabled
	// useMutex is false regardless of parallelismEnabled, because we do not do
	// parallel compression yet.
	c.sizeEstimate.useMutex = false

	// writeQueueSize determines the size of the write queue, or the number
	// of items which can be added to the queue without blocking. By default, we
	// use a writeQueue size of 0, since we won't be doing any block writes in
	// parallel.
	writeQueueSize := 0
	if parallelismEnabled {
		writeQueueSize = runtime.GOMAXPROCS(0)
	}
	c.writeQueue = newWriteQueue(writeQueueSize, writer)
}

// sizeEstimate is a general purpose helper for estimating two kinds of sizes:
// A. The compressed sstable size, which is useful for deciding when to start
//
//	a new sstable during flushes or compactions. In practice, we use this in
//	estimating the data size (excluding the index).
//
// B. The size of index blocks to decide when to start a new index block.
//
// There are some terminology peculiarities which are due to the origin of
// sizeEstimate for use case A with parallel compression enabled (for which
// the code has not been merged). Specifically this relates to the terms
// "written" and "compressed".
//   - The notion of "written" for case A is sufficiently defined by saying that
//     the data block is compressed. Waiting for the actual data block write to
//     happen can result in unnecessary estimation, when we already know how big
//     it will be in compressed form. Additionally, with the forthcoming value
//     blocks containing older MVCC values, these compressed block will be held
//     in-memory until late in the sstable writing, and we do want to accurately
//     account for them without waiting for the actual write.
//     For case B, "written" means that the index entry has been fully
//     generated, and has been added to the uncompressed block buffer for that
//     index block. It does not include actually writing a potentially
//     compressed index block.
//   - The notion of "compressed" is to differentiate between a "inflight" size
//     and the actual size, and is handled via computing a compression ratio
//     observed so far (defaults to 1).
//     For case A, this is actual data block compression, so the "inflight" size
//     is uncompressed blocks (that are no longer being written to) and the
//     "compressed" size is after they have been compressed.
//     For case B the inflight size is for a key-value pair in the index for
//     which the value size (the encoded size of the BlockHandleWithProperties)
//     is not accurately known, while the compressed size is the size of that
//     entry when it has been added to the (in-progress) index ssblock.
//
// Usage: To update state, one can optionally provide an inflight write value
// using addInflight (used for case B). When something is "written" the state
// can be updated using either writtenWithDelta or writtenWithTotal, which
// provide the actual delta size or the total size (latter must be
// monotonically non-decreasing). If there were no calls to addInflight, there
// isn't any real estimation happening here. So case A does not do any real
// estimation. However, when we introduce parallel compression, there will be
// estimation in that the client goroutine will call addInFlight and the
// compression goroutines will call writtenWithDelta.
type sizeEstimate struct {
	// emptySize is the size when there is no inflight data, and numEntries is 0.
	// emptySize is constant once set.
	emptySize uint64

	// inflightSize is the estimated size of some inflight data which hasn't
	// been written yet.
	inflightSize uint64

	// totalSize is the total size of the data which has already been written.
	totalSize uint64

	// numWrittenEntries is the total number of entries which have already been
	// written.
	numWrittenEntries uint64
	// numInflightEntries is the total number of entries which are inflight, and
	// haven't been written.
	numInflightEntries uint64

	// maxEstimatedSize stores the maximum result returned from sizeEstimate.size.
	// It ensures that values returned from subsequent calls to Writer.EstimatedSize
	// never decrease.
	maxEstimatedSize uint64

	// We assume that the entries added to the sizeEstimate can be compressed.
	// For this reason, we keep track of a compressedSize and an uncompressedSize
	// to compute a compression ratio for the inflight entries. If the entries
	// aren't being compressed, then compressedSize and uncompressedSize must be
	// equal.
	compressedSize   uint64
	uncompressedSize uint64
}

func (s *sizeEstimate) init(emptySize uint64) {
	s.emptySize = emptySize
}

func (s *sizeEstimate) size() uint64 {
	ratio := float64(1)
	if s.uncompressedSize > 0 {
		ratio = float64(s.compressedSize) / float64(s.uncompressedSize)
	}
	estimatedInflightSize := uint64(float64(s.inflightSize) * ratio)
	total := s.totalSize + estimatedInflightSize
	if total > s.maxEstimatedSize {
		s.maxEstimatedSize = total
	} else {
		total = s.maxEstimatedSize
	}

	if total == 0 {
		return s.emptySize
	}

	return total
}

func (s *sizeEstimate) numTotalEntries() uint64 {
	return s.numWrittenEntries + s.numInflightEntries
}

func (s *sizeEstimate) addInflight(size int) {
	s.numInflightEntries++
	s.inflightSize += uint64(size)
}

func (s *sizeEstimate) writtenWithTotal(newTotalSize uint64, inflightSize int) {
	finalEntrySize := int(newTotalSize - s.totalSize)
	s.writtenWithDelta(finalEntrySize, inflightSize)
}

func (s *sizeEstimate) writtenWithDelta(finalEntrySize int, inflightSize int) {
	if inflightSize > 0 {
		// This entry was previously inflight, so we should decrement inflight
		// entries and update the "compression" stats for future estimation.
		s.numInflightEntries--
		s.inflightSize -= uint64(inflightSize)
		s.uncompressedSize += uint64(inflightSize)
		s.compressedSize += uint64(finalEntrySize)
	}
	s.numWrittenEntries++
	s.totalSize += uint64(finalEntrySize)
}

func (s *sizeEstimate) clear() {
	*s = sizeEstimate{emptySize: s.emptySize}
}

type indexBlockBuf struct {
	// block will only be accessed from the writeQueue.
	block blockWriter

	size struct {
		useMutex bool
		mu       sync.Mutex
		estimate sizeEstimate
	}

	// restartInterval matches indexBlockBuf.block.restartInterval. We store it twice, because the `block`
	// must only be accessed from the writeQueue goroutine.
	restartInterval int
}

func (i *indexBlockBuf) clear() {
	i.block.clear()
	if i.size.useMutex {
		i.size.mu.Lock()
		defer i.size.mu.Unlock()
	}
	i.size.estimate.clear()
	i.restartInterval = 0
}

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

const indexBlockRestartInterval = 1

func newIndexBlockBuf(useMutex bool) *indexBlockBuf {
	i := indexBlockBufPool.Get().(*indexBlockBuf)
	i.size.useMutex = useMutex
	i.restartInterval = indexBlockRestartInterval
	i.block.restartInterval = indexBlockRestartInterval
	i.size.estimate.init(emptyBlockSize)
	return i
}

func (i *indexBlockBuf) shouldFlush(
	sep InternalKey, valueLen, targetBlockSize, sizeThreshold int,
) bool {
	if i.size.useMutex {
		i.size.mu.Lock()
		defer i.size.mu.Unlock()
	}

	nEntries := i.size.estimate.numTotalEntries()
	return shouldFlush(
		sep, valueLen, i.restartInterval, int(i.size.estimate.size()),
		int(nEntries), targetBlockSize, sizeThreshold)
}

func (i *indexBlockBuf) add(key InternalKey, value []byte, inflightSize int) {
	i.block.add(key, value)
	size := i.block.estimatedSize()
	if i.size.useMutex {
		i.size.mu.Lock()
		defer i.size.mu.Unlock()
	}
	i.size.estimate.writtenWithTotal(uint64(size), inflightSize)
}

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

func (i *indexBlockBuf) addInflight(inflightSize int) {
	if i.size.useMutex {
		i.size.mu.Lock()
		defer i.size.mu.Unlock()
	}
	i.size.estimate.addInflight(inflightSize)
}

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

	// Make sure that the size estimation works as expected when parallelism
	// is disabled.
	if invariants.Enabled && !i.size.useMutex {
		if i.size.estimate.inflightSize != 0 {
			panic("unexpected inflight entry in index block size estimation")
		}

		// NB: The i.block should only be accessed from the writeQueue goroutine,
		// when parallelism is enabled. We break that invariant here, but that's
		// okay since parallelism is disabled.
		if i.size.estimate.size() != uint64(i.block.estimatedSize()) {
			panic("index block size estimation sans parallelism is incorrect")
		}
	}
	return i.size.estimate.size()
}

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

	estimate sizeEstimate
}

// inflightSize is the uncompressed block size estimate which has been
// previously provided to addInflightDataBlock(). If addInflightDataBlock()
// has not been called, this must be set to 0. compressedSize is the
// compressed size of the block.
func (d *dataBlockEstimates) dataBlockCompressed(compressedSize int, inflightSize int) {
	if d.useMutex {
		d.mu.Lock()
		defer d.mu.Unlock()
	}
	d.estimate.writtenWithDelta(compressedSize+blockTrailerLen, inflightSize)
}

// size is an estimated size of datablock data which has been written to disk.
func (d *dataBlockEstimates) size() uint64 {
	if d.useMutex {
		d.mu.Lock()
		defer d.mu.Unlock()
	}
	// If there is no parallel compression, there should not be any inflight bytes.
	if invariants.Enabled && !d.useMutex {
		if d.estimate.inflightSize != 0 {
			panic("unexpected inflight entry in data block size estimation")
		}
	}
	return d.estimate.size()
}

// Avoid linter unused error.
var _ = (&dataBlockEstimates{}).addInflightDataBlock

// NB: unused since no parallel compression.
func (d *dataBlockEstimates) addInflightDataBlock(size int) {
	if d.useMutex {
		d.mu.Lock()
		defer d.mu.Unlock()
	}

	d.estimate.addInflight(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
}

func (b *blockBuf) clear() {
	// We can't assign b.compressedBuf[:0] to compressedBuf because snappy relies
	// on the length of the buffer, and not the capacity to determine if it needs
	// to make an allocation.
	*b = blockBuf{
		compressedBuf: b.compressedBuf, checksummer: b.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

	// We're making calls to BlockPropertyCollectors from the Writer client goroutine. We need to
	// pass the encoded block properties over to the write queue. To prevent copies, and allocations,
	// we give each dataBlockBuf, a blockPropertiesEncoder.
	blockPropsEncoder blockPropertiesEncoder
	// dataBlockProps is set when Writer.finishDataBlockProps is called. The dataBlockProps slice is
	// a shallow copy of the internal buffer of the dataBlockBuf.blockPropsEncoder.
	dataBlockProps []byte

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

func (d *dataBlockBuf) clear() {
	d.blockBuf.clear()
	d.dataBlock.clear()

	d.uncompressed = nil
	d.compressed = nil
	d.dataBlockProps = nil
	d.sepScratch = d.sepScratch[:0]
}

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)
}

func (d *dataBlockBuf) shouldFlush(
	key InternalKey, valueLen, targetBlockSize, sizeThreshold int,
) bool {
	return shouldFlush(
		key, valueLen, d.dataBlock.restartInterval, d.dataBlock.estimatedSize(),
		d.dataBlock.nEntries, targetBlockSize, sizeThreshold)
}

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. For a given Writer, the keys passed to Set must be in strictly increasing
// order.
//
// TODO(peter): untested
func (w *Writer) Set(key, value []byte) error {
	if w.err != nil {
		return w.err
	}
	if w.isStrictObsolete {
		return errors.Errorf("use AddWithForceObsolete")
	}
	// forceObsolete is false based on the assumption that no RANGEDELs in the
	// sstable delete the added points.
	return w.addPoint(base.MakeInternalKey(key, 0, InternalKeyKindSet), value, false)
}

// 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
	}
	if w.isStrictObsolete {
		return errors.Errorf("use AddWithForceObsolete")
	}
	// forceObsolete is false based on the assumption that no RANGEDELs in the
	// sstable delete the added points.
	return w.addPoint(base.MakeInternalKey(key, 0, InternalKeyKindDelete), nil, false)
}

// 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
	}
	if w.isStrictObsolete {
		return errors.Errorf("use AddWithForceObsolete")
	}
	// forceObsolete is false based on the assumption that no RANGEDELs in the
	// sstable that delete the added points. If the user configured this writer
	// to be strict-obsolete, addPoint will reject the addition of this MERGE.
	return w.addPoint(base.MakeInternalKey(key, 0, InternalKeyKindMerge), value, false)
}

// 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.isStrictObsolete {
		return errors.Errorf("use AddWithForceObsolete")
	}
	return w.AddWithForceObsolete(key, value, false)
}

// AddWithForceObsolete must be used when writing a strict-obsolete sstable.
//
// forceObsolete indicates whether the caller has determined that this key is
// obsolete even though it may be the latest point key for this userkey. This
// should be set to true for keys obsoleted by RANGEDELs, and is required for
// strict-obsolete sstables.
//
// Note that there are two properties, S1 and S2 (see comment in format.go)
// that strict-obsolete ssts must satisfy. S2, due to RANGEDELs, is solely the
// responsibility of the caller. S1 is solely the responsibility of the
// callee.
func (w *Writer) AddWithForceObsolete(key InternalKey, value []byte, forceObsolete bool) 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, forceObsolete)
}

func (w *Writer) makeAddPointDecisionV2(key InternalKey) error {
	prevTrailer := w.lastPointKeyInfo.trailer
	w.lastPointKeyInfo.trailer = key.Trailer
	if w.dataBlockBuf.dataBlock.nEntries == 0 {
		return nil
	}
	if !w.disableKeyOrderChecks {
		prevPointUserKey := w.dataBlockBuf.dataBlock.getCurUserKey()
		cmpUser := w.compare(prevPointUserKey, key.UserKey)
		if cmpUser > 0 || (cmpUser == 0 && prevTrailer <= key.Trailer) {
			return errors.Errorf(
				"pebble: keys must be added in strictly increasing order: %s, %s",
				InternalKey{UserKey: prevPointUserKey, Trailer: prevTrailer}.Pretty(w.formatKey),
				key.Pretty(w.formatKey))
		}
	}
	return nil
}

// REQUIRES: at least one point has been written to the Writer.
func (w *Writer) getLastPointUserKey() []byte {
	if w.dataBlockBuf.dataBlock.nEntries == 0 {
		panic(errors.AssertionFailedf("no point keys added to writer"))
	}
	return w.dataBlockBuf.dataBlock.getCurUserKey()
}

func (w *Writer) makeAddPointDecisionV3(
	key InternalKey, valueLen int,
) (setHasSamePrefix bool, writeToValueBlock bool, isObsolete bool, err error) {
	prevPointKeyInfo := w.lastPointKeyInfo
	w.lastPointKeyInfo.userKeyLen = len(key.UserKey)
	w.lastPointKeyInfo.prefixLen = w.lastPointKeyInfo.userKeyLen
	if w.split != nil {
		w.lastPointKeyInfo.prefixLen = w.split(key.UserKey)
	}
	w.lastPointKeyInfo.trailer = key.Trailer
	w.lastPointKeyInfo.isObsolete = false
	if !w.meta.HasPointKeys {
		return false, false, false, nil
	}
	keyKind := base.TrailerKind(key.Trailer)
	prevPointUserKey := w.getLastPointUserKey()
	prevPointKey := InternalKey{UserKey: prevPointUserKey, Trailer: prevPointKeyInfo.trailer}
	prevKeyKind := base.TrailerKind(prevPointKeyInfo.trailer)
	considerWriteToValueBlock := prevKeyKind == InternalKeyKindSet &&
		keyKind == InternalKeyKindSet
	if considerWriteToValueBlock && !w.requiredInPlaceValueBound.IsEmpty() {
		keyPrefix := key.UserKey[:w.lastPointKeyInfo.prefixLen]
		cmpUpper := w.compare(
			w.requiredInPlaceValueBound.Upper, keyPrefix)
		if cmpUpper <= 0 {
			// Common case for CockroachDB. Make it empty since all future keys in
			// this sstable will also have cmpUpper <= 0.
			w.requiredInPlaceValueBound = UserKeyPrefixBound{}
		} else if w.compare(keyPrefix, w.requiredInPlaceValueBound.Lower) >= 0 {
			considerWriteToValueBlock = false
		}
	}
	// cmpPrefix is initialized iff considerWriteToValueBlock.
	var cmpPrefix int
	var cmpUser int
	if considerWriteToValueBlock {
		// Compare the prefixes.
		cmpPrefix = w.compare(prevPointUserKey[:prevPointKeyInfo.prefixLen],
			key.UserKey[:w.lastPointKeyInfo.prefixLen])
		cmpUser = cmpPrefix
		if cmpPrefix == 0 {
			// Need to compare suffixes to compute cmpUser.
			cmpUser = w.compare(prevPointUserKey[prevPointKeyInfo.prefixLen:],
				key.UserKey[w.lastPointKeyInfo.prefixLen:])
		}
	} else {
		cmpUser = w.compare(prevPointUserKey, key.UserKey)
	}
	// Ensure that no one adds a point key kind without considering the obsolete
	// handling for that kind.
	switch keyKind {
	case InternalKeyKindSet, InternalKeyKindSetWithDelete, InternalKeyKindMerge,
		InternalKeyKindDelete, InternalKeyKindSingleDelete, InternalKeyKindDeleteSized:
	default:
		panic(errors.AssertionFailedf("unexpected key kind %s", keyKind.String()))
	}
	// If same user key, then the current key is obsolete if any of the
	// following is true:
	// C1 The prev key was obsolete.
	// C2 The prev key was not a MERGE. When the previous key is a MERGE we must
	//    preserve SET* and MERGE since their values will be merged into the
	//    previous key. We also must preserve DEL* since there may be an older
	//    SET*/MERGE in a lower level that must not be merged with the MERGE --
	//    if we omit the DEL* that lower SET*/MERGE will become visible.
	//
	// Regardless of whether it is the same user key or not
	// C3 The current key is some kind of point delete, and we are writing to
	//    the lowest level, then it is also obsolete. The correctness of this
	//    relies on the same user key not spanning multiple sstables in a level.
	//
	// C1 ensures that for a user key there is at most one transition from
	// !obsolete to obsolete. Consider a user key k, for which the first n keys
	// are not obsolete. We consider the various value of n:
	//
	// n = 0: This happens due to forceObsolete being set by the caller, or due
	// to C3. forceObsolete must only be set due a RANGEDEL, and that RANGEDEL
	// must also delete all the lower seqnums for the same user key. C3 triggers
	// due to a point delete and that deletes all the lower seqnums for the same
	// user key.
	//
	// n = 1: This is the common case. It happens when the first key is not a
	// MERGE, or the current key is some kind of point delete.
	//
	// n > 1: This is due to a sequence of MERGE keys, potentially followed by a
	// single non-MERGE key.
	isObsoleteC1AndC2 := cmpUser == 0 &&
		(prevPointKeyInfo.isObsolete || prevKeyKind != InternalKeyKindMerge)
	isObsoleteC3 := w.writingToLowestLevel &&
		(keyKind == InternalKeyKindDelete || keyKind == InternalKeyKindSingleDelete ||
			keyKind == InternalKeyKindDeleteSized)
	isObsolete = isObsoleteC1AndC2 || isObsoleteC3
	// TODO(sumeer): storing isObsolete SET and SETWITHDEL in value blocks is
	// possible, but requires some care in documenting and checking invariants.
	// There is code that assumes nothing in value blocks because of single MVCC
	// version (those should be ok). We have to ensure setHasSamePrefix is
	// correctly initialized here etc.

	if !w.disableKeyOrderChecks &&
		(cmpUser > 0 || (cmpUser == 0 && prevPointKeyInfo.trailer <= key.Trailer)) {
		return false, false, false, errors.Errorf(
			"pebble: keys must be added in strictly increasing order: %s, %s",
			prevPointKey.Pretty(w.formatKey), key.Pretty(w.formatKey))
	}
	if !considerWriteToValueBlock {
		return false, false, isObsolete, nil
	}
	// NB: it is possible that cmpUser == 0, i.e., these two SETs have identical
	// user keys (because of an open snapshot). This should be the rare case.
	setHasSamePrefix = cmpPrefix == 0
	considerWriteToValueBlock = setHasSamePrefix
	// Use of 0 here is somewhat arbitrary. Given the minimum 3 byte encoding of
	// valueHandle, this should be > 3. But tiny values are common in test and
	// unlikely in production, so we use 0 here for better test coverage.
	const tinyValueThreshold = 0
	if considerWriteToValueBlock && valueLen <= tinyValueThreshold {
		considerWriteToValueBlock = false
	}
	return setHasSamePrefix, considerWriteToValueBlock, isObsolete, nil
}

func (w *Writer) addPoint(key InternalKey, value []byte, forceObsolete bool) error {
	if w.isStrictObsolete && key.Kind() == InternalKeyKindMerge {
		return errors.Errorf("MERGE not supported in a strict-obsolete sstable")
	}
	var err error
	var setHasSameKeyPrefix, writeToValueBlock, addPrefixToValueStoredWithKey bool
	var isObsolete bool
	maxSharedKeyLen := len(key.UserKey)
	if w.valueBlockWriter != nil {
		// maxSharedKeyLen is limited to the prefix of the preceding key. If the
		// preceding key was in a different block, then the blockWriter will
		// ignore this maxSharedKeyLen.
		maxSharedKeyLen = w.lastPointKeyInfo.prefixLen
		setHasSameKeyPrefix, writeToValueBlock, isObsolete, err =
			w.makeAddPointDecisionV3(key, len(value))
		addPrefixToValueStoredWithKey = base.TrailerKind(key.Trailer) == InternalKeyKindSet
	} else {
		err = w.makeAddPointDecisionV2(key)
	}
	if err != nil {
		return err
	}
	isObsolete = w.tableFormat >= TableFormatPebblev4 && (isObsolete || forceObsolete)
	w.lastPointKeyInfo.isObsolete = isObsolete
	var valueStoredWithKey []byte
	var prefix valuePrefix
	var valueStoredWithKeyLen int
	if writeToValueBlock {
		vh, err := w.valueBlockWriter.addValue(value)
		if err != nil {
			return err
		}
		n := encodeValueHandle(w.blockBuf.tmp[:], vh)
		valueStoredWithKey = w.blockBuf.tmp[:n]
		valueStoredWithKeyLen = len(valueStoredWithKey) + 1
		var attribute base.ShortAttribute
		if w.shortAttributeExtractor != nil {
			// TODO(sumeer): for compactions, it is possible that the input sstable
			// already has this value in the value section and so we have already
			// extracted the ShortAttribute. Avoid extracting it again. This will
			// require changing the Writer.Add interface.
			if attribute, err = w.shortAttributeExtractor(
				key.UserKey, w.lastPointKeyInfo.prefixLen, value); err != nil {
				return err
			}
		}
		prefix = makePrefixForValueHandle(setHasSameKeyPrefix, attribute)
	} else {
		valueStoredWithKey = value
		valueStoredWithKeyLen = len(value)
		if addPrefixToValueStoredWithKey {
			valueStoredWithKeyLen++
		}
		prefix = makePrefixForInPlaceValue(setHasSameKeyPrefix)
	}

	if err := w.maybeFlush(key, valueStoredWithKeyLen); 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 {
		v := value
		if addPrefixToValueStoredWithKey {
			// Values for SET are not required to be in-place, and in the future may
			// not even be read by the compaction, so pass nil values. Block
			// property collectors in such Pebble DB's must not look at the value.
			v = nil
		}
		if err := w.blockPropCollectors[i].Add(key, v); err != nil {
			w.err = err
			return err
		}
	}
	if w.tableFormat >= TableFormatPebblev4 {
		w.obsoleteCollector.AddPoint(isObsolete)
	}

	w.maybeAddToFilter(key.UserKey)
	w.dataBlockBuf.dataBlock.addWithOptionalValuePrefix(
		key, isObsolete, valueStoredWithKey, maxSharedKeyLen, addPrefixToValueStoredWithKey, prefix,
		setHasSameKeyPrefix)

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

	if !w.meta.HasPointKeys {
		k := w.dataBlockBuf.dataBlock.getCurKey()
		// NB: We need to ensure that SmallestPoint.UserKey is set, so we create
		// an InternalKey which is semantically identical to the key, but won't
		// have a nil UserKey. We do this, because key.UserKey could be nil, and
		// we don't want SmallestPoint.UserKey to be nil.
		//
		// todo(bananabrick): Determine if it's okay to have a nil SmallestPoint
		// .UserKey now that we don't rely on a nil UserKey to determine if the
		// key has been set or not.
		w.meta.SetSmallestPointKey(k.Clone())
	}

	w.props.NumEntries++
	switch key.Kind() {
	case InternalKeyKindDelete, InternalKeyKindSingleDelete:
		w.props.NumDeletions++
		w.props.RawPointTombstoneKeySize += uint64(len(key.UserKey))
	case InternalKeyKindDeleteSized:
		var size uint64
		if len(value) > 0 {
			var n int
			size, n = binary.Uvarint(value)
			if n <= 0 {
				w.err = errors.Newf("%s key's value (%x) does not parse as uvarint",
					errors.Safe(key.Kind().String()), value)
				return w.err
			}
		}
		w.props.NumDeletions++
		w.props.NumSizedDeletions++
		w.props.RawPointTombstoneKeySize += uint64(len(key.UserKey))
		w.props.RawPointTombstoneValueSize += size
	case InternalKeyKindMerge:
		w.props.NumMergeOperands++
	}
	w.props.RawKeySize += uint64(key.Size())
	w.props.RawValueSize += uint64(len(value))
	return nil
}

func (w *Writer) prettyTombstone(k InternalKey, value []byte) fmt.Formatter {
	return keyspan.Span{
		Start: k.UserKey,
		End:   value,
		Keys:  []keyspan.Key{{Trailer: k.Trailer}},
	}.Pretty(w.formatKey)
}

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 := w.rangeDelBlock.getCurKey()
		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",
					w.prettyTombstone(prevKey, prevValue),
					w.prettyTombstone(key, value))
				return w.err
			}
			if prevKey.SeqNum() <= key.SeqNum() {
				w.err = errors.Errorf("pebble: keys must be added in strictly increasing 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",
					w.prettyTombstone(prevKey, prevValue),
					w.prettyTombstone(key, value))
				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.SetSmallestRangeDelKey(key.Clone())
			w.meta.SetLargestRangeDelKey(base.MakeRangeDeleteSentinelKey(value).Clone())
		} else {
			if base.InternalCompare(w.compare, w.meta.SmallestRangeDel, key) > 0 {
				w.meta.SetSmallestRangeDelKey(key.Clone())
			}
			end := base.MakeRangeDeleteSentinelKey(value)
			if base.InternalCompare(w.compare, w.meta.LargestRangeDel, end) < 0 {
				w.meta.SetLargestRangeDelKey(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.SetSmallestRangeDelKey(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. The resulting range key is given the
// sequence number zero, with the expectation that the resulting sstable will be
// ingested.
//
// Keys must be added to the table in increasing order of start key. Spans are
// not required to be fragmented. The same suffix may not be set or unset twice
// over the same keyspan, because it would result in inconsistent state. Both
// the Set and Unset would share the zero sequence number, and a key cannot be
// both simultaneously set and unset.
func (w *Writer) RangeKeySet(start, end, suffix, value []byte) error {
	return w.addRangeKeySpan(keyspan.Span{
		Start: w.tempRangeKeyCopy(start),
		End:   w.tempRangeKeyCopy(end),
		Keys: []keyspan.Key{
			{
				Trailer: base.MakeTrailer(0, base.InternalKeyKindRangeKeySet),
				Suffix:  w.tempRangeKeyCopy(suffix),
				Value:   w.tempRangeKeyCopy(value),
			},
		},
	})
}

// RangeKeyUnset un-sets a range between start (inclusive) and end (exclusive)
// with the given suffix. The resulting range key is given the
// sequence number zero, with the expectation that the resulting sstable will be
// ingested.
//
// Keys must be added to the table in increasing order of start key. Spans are
// not required to be fragmented. The same suffix may not be set or unset twice
// over the same keyspan, because it would result in inconsistent state. Both
// the Set and Unset would share the zero sequence number, and a key cannot be
// both simultaneously set and unset.
func (w *Writer) RangeKeyUnset(start, end, suffix []byte) error {
	return w.addRangeKeySpan(keyspan.Span{
		Start: w.tempRangeKeyCopy(start),
		End:   w.tempRangeKeyCopy(end),
		Keys: []keyspan.Key{
			{
				Trailer: base.MakeTrailer(0, base.InternalKeyKindRangeKeyUnset),
				Suffix:  w.tempRangeKeyCopy(suffix),
			},
		},
	})
}

// 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 {
	return w.addRangeKeySpan(keyspan.Span{
		Start: w.tempRangeKeyCopy(start),
		End:   w.tempRangeKeyCopy(end),
		Keys: []keyspan.Key{
			{Trailer: base.MakeTrailer(0, base.InternalKeyKindRangeKeyDelete)},
		},
	})
}

// 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(span keyspan.Span) error {
	if w.compare(span.Start, span.End) >= 0 {
		return errors.Errorf(
			"pebble: start key must be strictly less than end key",
		)
	}
	if w.fragmenter.Start() != nil && w.compare(w.fragmenter.Start(), span.Start) > 0 {
		return errors.Errorf("pebble: spans must be added in order: %s > %s",
			w.formatKey(w.fragmenter.Start()), w.formatKey(span.Start))
	}
	// Add this span to the fragmenter.
	w.fragmenter.Add(span)
	return w.err
}

func (w *Writer) encodeRangeKeySpan(span keyspan.Span) {
	// This method is the emit function of the Fragmenter.
	//
	// NB: The span should only contain range keys and be internally consistent
	// (eg, no duplicate suffixes, no additional keys after a RANGEKEYDEL).
	//
	// We use w.rangeKeysBySuffix and w.rangeKeySpan to avoid allocations.

	// Sort the keys by suffix. Iteration doesn't *currently* depend on it, but
	// we may want to in the future.
	w.rangeKeysBySuffix.Cmp = w.compare
	w.rangeKeysBySuffix.Keys = span.Keys
	sort.Sort(&w.rangeKeysBySuffix)

	w.rangeKeySpan = span
	w.rangeKeySpan.Keys = w.rangeKeysBySuffix.Keys
	w.err = firstError(w.err, w.rangeKeyEncoder.Encode(&w.rangeKeySpan))
}

func (w *Writer) addRangeKey(key InternalKey, value []byte) error {
	if !w.disableKeyOrderChecks && w.rangeKeyBlock.nEntries > 0 {
		prevStartKey := w.rangeKeyBlock.getCurKey()
		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",
				prevStartKey.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",
				curStartKey.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 increasing order: %s, %s",
				prevStartKey.Pretty(w.formatKey), key.Pretty(w.formatKey))
			return w.err
		}

		// Start keys are 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",
					prevStartKey.Pretty(w.formatKey),
					curStartKey.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",
				prevStartKey.Pretty(w.formatKey),
				curStartKey.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.SetSmallestRangeKey(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
}

// tempRangeKeyCopy returns a copy of the provided slice, stored in the Writer's
// range key buffer.
func (w *Writer) tempRangeKeyCopy(k []byte) []byte {
	if len(k) == 0 {
		return nil
	}
	buf := w.tempRangeKeyBuf(len(k))
	copy(buf, k)
	return buf
}

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 {
	// We're finishing a data block.
	err := w.finishDataBlockProps(w.dataBlockBuf)
	if err != nil {
		return err
	}
	w.dataBlockBuf.finish()
	w.dataBlockBuf.compressAndChecksum(w.compression)
	// Since dataBlockEstimates.addInflightDataBlock was never called, the
	// inflightSize is set to 0.
	w.coordination.sizeEstimate.dataBlockCompressed(len(w.dataBlockBuf.compressed), 0)

	// Determine if the index block should be flushed. Since we're accessing the
	// dataBlockBuf.dataBlock.curKey here, we have to make sure that once we start
	// to pool the dataBlockBufs, the curKey isn't used by the Writer once the
	// dataBlockBuf is added back to a sync.Pool. In this particular case, the
	// byte slice which supports "sep" will eventually be copied when "sep" is
	// added to the index block.
	prevKey := w.dataBlockBuf.dataBlock.getCurKey()
	sep := w.indexEntrySep(prevKey, key, w.dataBlockBuf)
	// We determine that we should flush an index block from the Writer client
	// goroutine, but we actually finish the index block from the writeQueue.
	// When we determine that an index block should be flushed, we need to call
	// BlockPropertyCollector.FinishIndexBlock. But block property collector
	// calls must happen sequentially from the Writer client. Therefore, we need
	// to determine that we are going to flush the index block from the Writer
	// client.
	shouldFlushIndexBlock := supportsTwoLevelIndex(w.tableFormat) && w.indexBlock.shouldFlush(
		sep, encodedBHPEstimatedSize, w.indexBlockSize, w.indexBlockSizeThreshold,
	)

	var indexProps []byte
	var flushableIndexBlock *indexBlockBuf
	if shouldFlushIndexBlock {
		flushableIndexBlock = w.indexBlock
		w.indexBlock = newIndexBlockBuf(w.coordination.parallelismEnabled)
		// Call BlockPropertyCollector.FinishIndexBlock, since we've decided to
		// flush the index block.
		indexProps, err = w.finishIndexBlockProps()
		if err != nil {
			return err
		}
	}

	// We've called BlockPropertyCollector.FinishDataBlock, and, if necessary,
	// BlockPropertyCollector.FinishIndexBlock. Since we've decided to finish
	// the data block, we can call
	// BlockPropertyCollector.AddPrevDataBlockToIndexBlock.
	w.addPrevDataBlockToIndexBlockProps()

	// Schedule a write.
	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.indexEntrySep = sep
	writeTask.currIndexBlock = w.indexBlock
	writeTask.indexInflightSize = sep.Size() + encodedBHPEstimatedSize
	writeTask.finishedIndexProps = indexProps
	writeTask.flushableIndexBlock = flushableIndexBlock

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

	w.dataBlockBuf = nil
	if w.coordination.parallelismEnabled {
		w.coordination.writeQueue.add(writeTask)
	} else {
		err = w.coordination.writeQueue.addSync(writeTask)
	}
	w.dataBlockBuf = newDataBlockBuf(w.restartInterval, w.checksumType)

	return err
}

func (w *Writer) maybeFlush(key InternalKey, valueLen int) error {
	if !w.dataBlockBuf.shouldFlush(key, valueLen, w.blockSize, w.blockSizeThreshold) {
		return nil
	}

	err := w.flush(key)

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

	return nil
}

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

	buf.dataBlockProps = buf.blockPropsEncoder.unsafeProps()
	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.
// maybeAddBlockPropertiesToBlockHandle should only be called if block is being written synchronously
// with the Writer client.
func (w *Writer) maybeAddBlockPropertiesToBlockHandle(
	bh BlockHandle,
) (BlockHandleWithProperties, error) {
	err := w.finishDataBlockProps(w.dataBlockBuf)
	if err != nil {
		return BlockHandleWithProperties{}, err
	}
	return BlockHandleWithProperties{BlockHandle: bh, Props: w.dataBlockBuf.dataBlockProps}, nil
}

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

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

// addIndexEntry adds an index entry for the specified key and block handle.
// addIndexEntry can be called from both the Writer client goroutine, and the
// writeQueue goroutine. If the flushIndexBuf != nil, then the indexProps, as
// they're used when the index block is finished.
//
// Invariant:
//  1. addIndexEntry must not store references to the sep InternalKey, the tmp
//     byte slice, bhp.Props. That is, these must be either deep copied or
//     encoded.
//  2. addIndexEntry must not hold references to the flushIndexBuf, and the writeTo
//     indexBlockBufs.
func (w *Writer) addIndexEntry(
	sep InternalKey,
	bhp BlockHandleWithProperties,
	tmp []byte,
	flushIndexBuf *indexBlockBuf,
	writeTo *indexBlockBuf,
	inflightSize int,
	indexProps []byte,
) error {
	if bhp.Length == 0 {
		// A valid blockHandle must be non-zero.
		// In particular, it must have a non-zero length.
		return nil
	}

	encoded := encodeBlockHandleWithProperties(tmp, bhp)

	if flushIndexBuf != nil {
		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(flushIndexBuf, indexProps); err != nil {
			return err
		}
	}

	writeTo.add(sep, encoded, inflightSize)
	return nil
}

func (w *Writer) addPrevDataBlockToIndexBlockProps() {
	for i := range w.blockPropCollectors {
		w.blockPropCollectors[i].AddPrevDataBlockToIndexBlock()
	}
}

// addIndexEntrySync adds an index entry for the specified key and block handle.
// Writer.addIndexEntry is only called synchronously once Writer.Close is called.
// addIndexEntrySync should only be called if we're sure that index entries
// aren't being written asynchronously.
//
// Invariant:
//  1. addIndexEntrySync must not store references to the prevKey, key InternalKey's,
//     the tmp byte slice. That is, these must be either deep copied or encoded.
func (w *Writer) addIndexEntrySync(
	prevKey, key InternalKey, bhp BlockHandleWithProperties, tmp []byte,
) error {
	sep := w.indexEntrySep(prevKey, key, w.dataBlockBuf)
	shouldFlush := supportsTwoLevelIndex(
		w.tableFormat) && w.indexBlock.shouldFlush(
		sep, encodedBHPEstimatedSize, w.indexBlockSize, w.indexBlockSizeThreshold,
	)
	var flushableIndexBlock *indexBlockBuf
	var props []byte
	var err error
	if shouldFlush {
		flushableIndexBlock = w.indexBlock
		w.indexBlock = newIndexBlockBuf(w.coordination.parallelismEnabled)

		// Call BlockPropertyCollector.FinishIndexBlock, since we've decided to
		// flush the index block.
		props, err = w.finishIndexBlockProps()
		if err != nil {
			return err
		}
	}

	err = w.addIndexEntry(sep, bhp, tmp, flushableIndexBlock, w.indexBlock, 0, props)
	if flushableIndexBlock != nil {
		flushableIndexBlock.clear()
		indexBlockBufPool.Put(flushableIndexBlock)
	}
	w.addPrevDataBlockToIndexBlockProps()
	return err
}

func shouldFlush(
	key InternalKey,
	valueLen int,
	restartInterval, estimatedBlockSize, numEntries, targetBlockSize, sizeThreshold int,
) bool {
	if numEntries == 0 {
		return false
	}

	if estimatedBlockSize >= targetBlockSize {
		return true
	}

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

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

func cloneKeyWithBuf(k InternalKey, a bytealloc.A) (bytealloc.A, InternalKey) {
	if len(k.UserKey) == 0 {
		return a, k
	}
	a, keyCopy := a.Copy(k.UserKey)
	return a, InternalKey{UserKey: keyCopy, Trailer: k.Trailer}
}

// Invariants: The byte slice returned by finishIndexBlockProps is heap-allocated
//
//	and has its own lifetime, independent of the Writer and the blockPropsEncoder,
//
// and it is safe to:
//  1. Reuse w.blockPropsEncoder without first encoding the byte slice returned.
//  2. Store the byte slice in the Writer since it is a copy and not supported by
//     an underlying buffer.
func (w *Writer) finishIndexBlockProps() ([]byte, 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 nil, err
		}
		if len(scratch) > 0 {
			w.blockPropsEncoder.addProp(shortID(i), scratch)
		}
	}
	return w.blockPropsEncoder.props(), nil
}

// 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.
//
// Invariants:
//  1. The props slice passed into finishedIndexBlock must not be a
//     owned by any other struct, since it will be stored in the Writer.indexPartitions
//     slice.
//  2. None of the buffers owned by indexBuf will be shallow copied and stored elsewhere.
//     That is, it must be safe to reuse indexBuf after finishIndexBlock has been called.
func (w *Writer) finishIndexBlock(indexBuf *indexBlockBuf, props []byte) error {
	part := indexBlockAndBlockProperties{
		nEntries: indexBuf.block.nEntries, properties: props,
	}
	w.indexSepAlloc, part.sep = cloneKeyWithBuf(
		indexBuf.block.getCurKey(), w.indexSepAlloc,
	)
	bk := indexBuf.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) {
	props, err := w.finishIndexBlockProps()
	if err != nil {
		return BlockHandle{}, err
	}
	// Add the final unfinished index.
	if err = w.finishIndexBlock(w.indexBlock, props); 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.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.
	if err := w.writable.Write(block); err != nil {
		return BlockHandle{}, err
	}
	w.meta.Size += uint64(len(block))
	if err := w.writable.Write(blockTrailerBuf[:blockTrailerLen]); err != nil {
		return BlockHandle{}, err
	}
	w.meta.Size += blockTrailerLen

	return bh, nil
}

// Write implements io.Writer. This is analogous to writeCompressedBlock for
// blocks that already incorporate the trailer, and don't need the callee to
// return a BlockHandle.
func (w *Writer) Write(blockWithTrailer []byte) (n int, err error) {
	offset := w.meta.Size
	if w.cacheID != 0 && w.fileNum.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, offset)
	}
	w.meta.Size += uint64(len(blockWithTrailer))
	if err := w.writable.Write(blockWithTrailer); err != nil {
		return 0, err
	}
	return len(blockWithTrailer), 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,
		)
	}

	// PebbleDBv3: value blocks.
	if (w.props.NumValueBlocks > 0 || w.props.NumValuesInValueBlocks > 0 ||
		w.props.ValueBlocksSize > 0) && w.tableFormat < TableFormatPebblev3 {
		return errors.Newf(
			"table format version %s is less than the minimum required version %s for value blocks",
			w.tableFormat, TableFormatPebblev3)
	}

	// PebbleDBv4: DELSIZED tombstones.
	if w.props.NumSizedDeletions > 0 && w.tableFormat < TableFormatPebblev4 {
		return errors.Newf(
			"table format version %s is less than the minimum required version %s for sized deletion tombstones",
			w.tableFormat, TableFormatPebblev4)
	}
	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.valueBlockWriter != nil {
			releaseValueBlockWriter(w.valueBlockWriter)
			// Defensive code in case Close gets called again. We don't want to put
			// the same object to a sync.Pool.
			w.valueBlockWriter = nil
		}
		if w.writable != nil {
			w.writable.Abort()
			w.writable = nil
		}
		// Record any error in the writer (so we can exit early if Close is called
		// again).
		if err != nil {
			w.err = err
		}
	}()

	// 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 {
		return err
	}

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

	// The w.meta.LargestPointKey is only used once the Writer is closed, so it is safe to set it
	// when the Writer is closed.
	//
	// The following invariants ensure that setting the largest key at this point of a Writer close
	// is correct:
	// 1. Keys must only be added to the Writer in an increasing order.
	// 2. The current w.dataBlockBuf is guaranteed to have the latest key added to the Writer. This
	//    must be true, because a w.dataBlockBuf is only switched out when a dataBlock is flushed,
	//    however, if a dataBlock is flushed, then we add a key to the new w.dataBlockBuf in the
	//    addPoint function after the flush occurs.
	if w.dataBlockBuf.dataBlock.nEntries >= 1 {
		w.meta.SetLargestPointKey(w.dataBlockBuf.dataBlock.getCurKey().Clone())
	}

	// 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 {
			return err
		}
		bhp, err := w.maybeAddBlockPropertiesToBlockHandle(bh)
		if err != nil {
			return err
		}
		prevKey := w.dataBlockBuf.dataBlock.getCurKey()
		if err := w.addIndexEntrySync(prevKey, InternalKey{}, bhp, w.dataBlockBuf.tmp[:]); err != nil {
			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 {
			return err
		}
		bh, err := w.writeBlock(b, NoCompression, &w.blockBuf)
		if err != nil {
			return 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 {
			return 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.estimatedSize()) + 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 {
			return 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.
			k := base.MakeRangeDeleteSentinelKey(w.rangeDelBlock.curValue).Clone()
			w.meta.SetLargestRangeDelKey(k)
		}
		rangeDelBH, err = w.writeBlock(w.rangeDelBlock.finish(), NoCompression, &w.blockBuf)
		if err != nil {
			return 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 := w.rangeKeyBlock.getCurKey()
		kind := key.Kind()
		endKey, _, ok := rangekey.DecodeEndKey(kind, w.rangeKeyBlock.curValue)
		if !ok {
			return errors.Newf("invalid end key: %s", w.rangeKeyBlock.curValue)
		}
		k := base.MakeExclusiveSentinelKey(kind, endKey).Clone()
		w.meta.SetLargestRangeKey(k)
		// 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 {
			return err
		}
	}

	if w.valueBlockWriter != nil {
		vbiHandle, vbStats, err := w.valueBlockWriter.finish(w, w.meta.Size)
		if err != nil {
			return err
		}
		w.props.NumValueBlocks = vbStats.numValueBlocks
		w.props.NumValuesInValueBlocks = vbStats.numValuesInValueBlocks
		w.props.ValueBlocksSize = vbStats.valueBlocksAndIndexSize
		if vbStats.numValueBlocks > 0 {
			n := encodeValueBlocksIndexHandle(w.blockBuf.tmp[:], vbiHandle)
			metaindex.add(InternalKey{UserKey: []byte(metaValueIndexName)}, w.blockBuf.tmp[:n])
		}
	}

	// 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 {
				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 {
				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(w.tableFormat, &raw)
		bh, err := w.writeBlock(raw.finish(), NoCompression, &w.blockBuf)
		if err != nil {
			return 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 {
		return err
	}

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

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

	if err := w.writable.Finish(); err != nil {
		w.writable = nil
		return err
	}
	w.writable = nil

	w.dataBlockBuf.clear()
	dataBlockBufPool.Put(w.dataBlockBuf)
	w.dataBlockBuf = nil
	w.indexBlock.clear()
	indexBlockBufPool.Put(w.indexBlock)
	w.indexBlock = nil

	// 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
// call 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.estimatedSize()
}

// 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.writable != 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 to the Writer. The value's lifetime ends the next time a
// point key is added to the Writer.
// Invariant: UnsafeKey isn't and shouldn't be called after the Writer is closed.
func (o PreviousPointKeyOpt) UnsafeKey() base.InternalKey {
	if o.w == nil {
		return base.InvalidInternalKey
	}

	if o.w.dataBlockBuf.dataBlock.nEntries >= 1 {
		// o.w.dataBlockBuf.dataBlock.curKey is guaranteed to point to the last point key
		// which was added to the Writer.
		return o.w.dataBlockBuf.dataBlock.getCurKey()
	}
	return base.InternalKey{}
}

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

// NewWriter returns a new table writer for the file. Closing the writer will
// close the file.
func NewWriter(writable objstorage.Writable, o WriterOptions, extraOpts ...WriterOption) *Writer {
	o = o.ensureDefaults()
	w := &Writer{
		writable: writable,
		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,
		isStrictObsolete:        o.IsStrictObsolete,
		writingToLowestLevel:    o.WritingToLowestLevel,
		cache:                   o.Cache,
		restartInterval:         o.BlockRestartInterval,
		checksumType:            o.Checksum,
		indexBlock:              newIndexBlockBuf(o.Parallelism),
		rangeDelBlock: blockWriter{
			restartInterval: 1,
		},
		rangeKeyBlock: blockWriter{
			restartInterval: 1,
		},
		topLevelIndexBlock: blockWriter{
			restartInterval: 1,
		},
		fragmenter: keyspan.Fragmenter{
			Cmp:    o.Comparer.Compare,
			Format: o.Comparer.FormatKey,
		},
	}
	if w.tableFormat >= TableFormatPebblev3 {
		w.shortAttributeExtractor = o.ShortAttributeExtractor
		w.requiredInPlaceValueBound = o.RequiredInPlaceValueBound
		w.valueBlockWriter = newValueBlockWriter(
			w.blockSize, w.blockSizeThreshold, w.compression, w.checksumType, func(compressedSize int) {
				w.coordination.sizeEstimate.dataBlockCompressed(compressedSize, 0)
			})
	}

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

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

	w.coordination.init(o.Parallelism, w)

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

	// Note that WriterOptions are applied in two places; the ones with a
	// preApply() method are applied here. The rest are applied down below 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.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 ||
		w.tableFormat >= TableFormatPebblev4 {
		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())
			}
		}
		numBlockPropertyCollectors := len(o.BlockPropertyCollectors)
		if w.tableFormat >= TableFormatPebblev4 {
			numBlockPropertyCollectors++
		}
		// shortID is a uint8, so we cannot exceed that number of block
		// property collectors.
		if numBlockPropertyCollectors > math.MaxUint8 {
			w.err = errors.New("pebble: too many block property collectors")
			return w
		}
		if numBlockPropertyCollectors > 0 {
			w.blockPropCollectors = make([]BlockPropertyCollector, numBlockPropertyCollectors)
		}
		if len(o.BlockPropertyCollectors) > 0 {
			// The shortID assigned to a collector is the same as its index in
			// this slice.
			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())
			}
		}
		if w.tableFormat >= TableFormatPebblev4 {
			if numBlockPropertyCollectors > 1 || len(o.TablePropertyCollectors) > 0 {
				buf.WriteString(",")
			}
			w.blockPropCollectors[numBlockPropertyCollectors-1] = &w.obsoleteCollector
			buf.WriteString(w.obsoleteCollector.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 {
			continue
		}
		opt.writerApply(w)
	}

	// Initialize the range key fragmenter and encoder.
	w.fragmenter.Emit = w.encodeRangeKeySpan
	w.rangeKeyEncoder.Emit = w.addRangeKey
	return w
}

// internalGetProperties is a private, internal-use-only function that takes a
// Writer and returns a pointer to its Properties, allowing direct mutation.
// It's used by internal Pebble flushes and compactions to set internal
// properties. It gets installed in private.
func internalGetProperties(w *Writer) *Properties {
	return &w.props
}

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

type obsoleteKeyBlockPropertyCollector struct {
	blockIsNonObsolete bool
	indexIsNonObsolete bool
	tableIsNonObsolete bool
}

func encodeNonObsolete(isNonObsolete bool, buf []byte) []byte {
	if isNonObsolete {
		return buf
	}
	return append(buf, 't')
}

func (o *obsoleteKeyBlockPropertyCollector) Name() string {
	return "obsolete-key"
}

func (o *obsoleteKeyBlockPropertyCollector) Add(key InternalKey, value []byte) error {
	// Ignore.
	return nil
}

func (o *obsoleteKeyBlockPropertyCollector) AddPoint(isObsolete bool) {
	o.blockIsNonObsolete = o.blockIsNonObsolete || !isObsolete
}

func (o *obsoleteKeyBlockPropertyCollector) FinishDataBlock(buf []byte) ([]byte, error) {
	o.tableIsNonObsolete = o.tableIsNonObsolete || o.blockIsNonObsolete
	return encodeNonObsolete(o.blockIsNonObsolete, buf), nil
}

func (o *obsoleteKeyBlockPropertyCollector) AddPrevDataBlockToIndexBlock() {
	o.indexIsNonObsolete = o.indexIsNonObsolete || o.blockIsNonObsolete
	o.blockIsNonObsolete = false
}

func (o *obsoleteKeyBlockPropertyCollector) FinishIndexBlock(buf []byte) ([]byte, error) {
	indexIsNonObsolete := o.indexIsNonObsolete
	o.indexIsNonObsolete = false
	return encodeNonObsolete(indexIsNonObsolete, buf), nil
}

func (o *obsoleteKeyBlockPropertyCollector) FinishTable(buf []byte) ([]byte, error) {
	return encodeNonObsolete(o.tableIsNonObsolete, buf), nil
}

func (o *obsoleteKeyBlockPropertyCollector) UpdateKeySuffixes(
	oldProp []byte, oldSuffix, newSuffix []byte,
) error {
	_, err := propToIsObsolete(oldProp)
	if err != nil {
		return err
	}
	// Suffix rewriting currently loses the obsolete bit.
	o.blockIsNonObsolete = true
	return nil
}

// NB: obsoleteKeyBlockPropertyFilter is stateless. This aspect of the filter
// is used in table_cache.go for in-place modification of a filters slice.
type obsoleteKeyBlockPropertyFilter struct{}

func (o obsoleteKeyBlockPropertyFilter) Name() string {
	return "obsolete-key"
}

// Intersects returns true if the set represented by prop intersects with
// the set in the filter.
func (o obsoleteKeyBlockPropertyFilter) Intersects(prop []byte) (bool, error) {
	return propToIsObsolete(prop)
}

func propToIsObsolete(prop []byte) (bool, error) {
	if len(prop) == 0 {
		return true, nil
	}
	if len(prop) > 1 || prop[0] != 't' {
		return false, errors.Errorf("unexpected property %x", prop)
	}
	return false, nil
}