ceremonyclient/pebble/internal/rangekey/rangekey.go
Cassandra Heart 2e2a1e4789
v1.2.0 (#31)
2024-01-03 01:31:42 -06:00

412 lines
14 KiB
Go

// Copyright 2021 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 rangekey provides facilities for encoding, decoding and merging range
// keys.
//
// Range keys map a span of keyspan `[start, end)`, at an optional suffix, to a
// value.
//
// # Encoding
//
// Unlike other Pebble keys, range keys encode several fields of information:
// start key, end key, suffix and value. Internally within Pebble and its
// sstables, all keys including range keys are represented as a key-value tuple.
// Range keys map to internal key-value tuples by mapping the start key to the
// key and encoding the remainder of the fields in the value.
//
// ## `RANGEKEYSET`
//
// A `RANGEKEYSET` represents one more range keys set over a single region of
// user key space. Each represented range key must have a unique suffix. A
// `RANGEKEYSET` encapsulates a start key, an end key and a set of SuffixValue
// pairs.
//
// A `RANGEKEYSET` key's user key holds the start key. Its value is a varstring
// end key, followed by a set of SuffixValue pairs. A `RANGEKEYSET` may have
// multiple SuffixValue pairs if the keyspan was set at multiple unique suffix
// values.
//
// ## `RANGEKEYUNSET`
//
// A `RANGEKEYUNSET` represents the removal of range keys at specific suffixes
// over a single region of user key space. A `RANGEKEYUNSET` encapsulates a
// start key, an end key and a set of suffixes.
//
// A `RANGEKEYUNSET` key's user key holds the start key. Its value is a
// varstring end key, followed by a set of suffixes. A `RANGEKEYUNSET` may have
// multiple suffixes if the keyspan was unset at multiple unique suffixes.
//
// ## `RANGEKEYDEL`
//
// A `RANGEKEYDEL` represents the removal of all range keys over a single region
// of user key space, regardless of suffix. A `RANGEKEYDEL` encapsulates a
// start key and an end key. The end key is stored in the value, without any
// varstring length prefixing.
package rangekey
// TODO(jackson): Document the encoding of RANGEKEYSET and RANGEKEYUNSET values
// once we're confident they're stable.
import (
"encoding/binary"
"github.com/cockroachdb/errors"
"github.com/cockroachdb/pebble/internal/base"
"github.com/cockroachdb/pebble/internal/keyspan"
)
// Encode takes a Span containing only range keys. It invokes the provided
// closure with the encoded internal keys that represent the Span's state. The
// keys and values passed to emit are only valid until the closure returns.
// If emit returns an error, Encode stops and returns the error.
func Encode(s *keyspan.Span, emit func(k base.InternalKey, v []byte) error) error {
enc := Encoder{Emit: emit}
return enc.Encode(s)
}
// An Encoder encodes range keys into their on-disk InternalKey format. An
// Encoder holds internal buffers, reused between Emit calls.
type Encoder struct {
Emit func(base.InternalKey, []byte) error
buf []byte
unsets [][]byte
sets []SuffixValue
}
// Encode takes a Span containing only range keys. It invokes the Encoder's Emit
// closure with the encoded internal keys that represent the Span's state. The
// keys and values passed to emit are only valid until the closure returns. If
// Emit returns an error, Encode stops and returns the error.
//
// The encoded key-value pair passed to Emit is only valid until the closure
// completes.
func (e *Encoder) Encode(s *keyspan.Span) error {
if s.Empty() {
return nil
}
// This for loop iterates through the span's keys, which are sorted by
// sequence number descending, grouping them into sequence numbers. All keys
// with identical sequence numbers are flushed together.
var del bool
var seqNum uint64
for i := range s.Keys {
if i == 0 || s.Keys[i].SeqNum() != seqNum {
if i > 0 {
// Flush all the existing internal keys that exist at seqNum.
if err := e.flush(s, seqNum, del); err != nil {
return err
}
}
// Reset sets, unsets, del.
seqNum = s.Keys[i].SeqNum()
del = false
e.sets = e.sets[:0]
e.unsets = e.unsets[:0]
}
switch s.Keys[i].Kind() {
case base.InternalKeyKindRangeKeySet:
e.sets = append(e.sets, SuffixValue{
Suffix: s.Keys[i].Suffix,
Value: s.Keys[i].Value,
})
case base.InternalKeyKindRangeKeyUnset:
e.unsets = append(e.unsets, s.Keys[i].Suffix)
case base.InternalKeyKindRangeKeyDelete:
del = true
default:
return base.CorruptionErrorf("pebble: %s key kind is not a range key", s.Keys[i].Kind())
}
}
return e.flush(s, seqNum, del)
}
// flush constructs internal keys for accumulated key state, and emits the
// internal keys.
func (e *Encoder) flush(s *keyspan.Span, seqNum uint64, del bool) error {
if len(e.sets) > 0 {
ik := base.MakeInternalKey(s.Start, seqNum, base.InternalKeyKindRangeKeySet)
l := EncodedSetValueLen(s.End, e.sets)
if l > cap(e.buf) {
e.buf = make([]byte, l)
}
EncodeSetValue(e.buf[:l], s.End, e.sets)
if err := e.Emit(ik, e.buf[:l]); err != nil {
return err
}
}
if len(e.unsets) > 0 {
ik := base.MakeInternalKey(s.Start, seqNum, base.InternalKeyKindRangeKeyUnset)
l := EncodedUnsetValueLen(s.End, e.unsets)
if l > cap(e.buf) {
e.buf = make([]byte, l)
}
EncodeUnsetValue(e.buf[:l], s.End, e.unsets)
if err := e.Emit(ik, e.buf[:l]); err != nil {
return err
}
}
if del {
ik := base.MakeInternalKey(s.Start, seqNum, base.InternalKeyKindRangeKeyDelete)
// s.End is stored directly in the value for RangeKeyDeletes.
if err := e.Emit(ik, s.End); err != nil {
return err
}
}
return nil
}
// Decode takes an internal key pair encoding range key(s) and returns a decoded
// keyspan containing the keys. If keysDst is provided, keys will be appended to
// keysDst.
func Decode(ik base.InternalKey, v []byte, keysDst []keyspan.Key) (keyspan.Span, error) {
var s keyspan.Span
// Hydrate the user key bounds.
s.Start = ik.UserKey
var ok bool
s.End, v, ok = DecodeEndKey(ik.Kind(), v)
if !ok {
return keyspan.Span{}, base.CorruptionErrorf("pebble: unable to decode range key end from %s", ik.Kind())
}
s.Keys = keysDst
// Hydrate the contents of the range key(s).
switch ik.Kind() {
case base.InternalKeyKindRangeKeySet:
for len(v) > 0 {
var sv SuffixValue
sv, v, ok = decodeSuffixValue(v)
if !ok {
return keyspan.Span{}, base.CorruptionErrorf("pebble: unable to decode range key suffix-value tuple")
}
s.Keys = append(s.Keys, keyspan.Key{
Trailer: ik.Trailer,
Suffix: sv.Suffix,
Value: sv.Value,
})
}
case base.InternalKeyKindRangeKeyUnset:
for len(v) > 0 {
var suffix []byte
suffix, v, ok = decodeSuffix(v)
if !ok {
return keyspan.Span{}, base.CorruptionErrorf("pebble: unable to decode range key unset suffix")
}
s.Keys = append(s.Keys, keyspan.Key{
Trailer: ik.Trailer,
Suffix: suffix,
})
}
case base.InternalKeyKindRangeKeyDelete:
if len(v) > 0 {
return keyspan.Span{}, base.CorruptionErrorf("pebble: RANGEKEYDELs must not contain additional data")
}
s.Keys = append(s.Keys, keyspan.Key{Trailer: ik.Trailer})
default:
return keyspan.Span{}, base.CorruptionErrorf("pebble: %s is not a range key", ik.Kind())
}
return s, nil
}
// SuffixValue represents a tuple of a suffix and a corresponding value. A
// physical RANGEKEYSET key may contain many logical RangeKeySets, each
// represented with a separate SuffixValue tuple.
type SuffixValue struct {
Suffix []byte
Value []byte
}
// encodedSetSuffixValuesLen precomputes the length of the given slice of
// SuffixValues, when encoded for a RangeKeySet. It may be used to construct a
// buffer of the appropriate size before encoding.
func encodedSetSuffixValuesLen(suffixValues []SuffixValue) int {
var n int
for i := 0; i < len(suffixValues); i++ {
n += lenVarint(len(suffixValues[i].Suffix))
n += len(suffixValues[i].Suffix)
n += lenVarint(len(suffixValues[i].Value))
n += len(suffixValues[i].Value)
}
return n
}
// encodeSetSuffixValues encodes a slice of SuffixValues for a RangeKeySet into
// dst. The length of dst must be greater than or equal to
// encodedSetSuffixValuesLen. encodeSetSuffixValues returns the number of bytes
// written, which should always equal the EncodedSetValueLen with the same
// arguments.
func encodeSetSuffixValues(dst []byte, suffixValues []SuffixValue) int {
// Encode the list of (suffix, value-len) tuples.
var n int
for i := 0; i < len(suffixValues); i++ {
// Encode the length of the suffix.
n += binary.PutUvarint(dst[n:], uint64(len(suffixValues[i].Suffix)))
// Encode the suffix itself.
n += copy(dst[n:], suffixValues[i].Suffix)
// Encode the value length.
n += binary.PutUvarint(dst[n:], uint64(len(suffixValues[i].Value)))
// Encode the value itself.
n += copy(dst[n:], suffixValues[i].Value)
}
return n
}
// EncodedSetValueLen precomputes the length of a RangeKeySet's value when
// encoded. It may be used to construct a buffer of the appropriate size before
// encoding.
func EncodedSetValueLen(endKey []byte, suffixValues []SuffixValue) int {
n := lenVarint(len(endKey))
n += len(endKey)
n += encodedSetSuffixValuesLen(suffixValues)
return n
}
// EncodeSetValue encodes a RangeKeySet's value into dst. The length of dst must
// be greater than or equal to EncodedSetValueLen. EncodeSetValue returns the
// number of bytes written, which should always equal the EncodedSetValueLen
// with the same arguments.
func EncodeSetValue(dst []byte, endKey []byte, suffixValues []SuffixValue) int {
// First encode the end key as a varstring.
n := binary.PutUvarint(dst, uint64(len(endKey)))
n += copy(dst[n:], endKey)
n += encodeSetSuffixValues(dst[n:], suffixValues)
return n
}
// DecodeEndKey reads the end key from the beginning of a range key (RANGEKEYSET,
// RANGEKEYUNSET or RANGEKEYDEL)'s physical encoded value. Both sets and unsets
// encode the range key, plus additional data in the value.
func DecodeEndKey(kind base.InternalKeyKind, data []byte) (endKey, value []byte, ok bool) {
switch kind {
case base.InternalKeyKindRangeKeyDelete:
// No splitting is necessary for range key deletes. The value is the end
// key, and there is no additional associated value.
return data, nil, true
case base.InternalKeyKindRangeKeySet, base.InternalKeyKindRangeKeyUnset:
v, n := binary.Uvarint(data)
if n <= 0 || uint64(n)+v >= uint64(len(data)) {
return nil, nil, false
}
endKey, value = data[n:n+int(v)], data[n+int(v):]
return endKey, value, true
default:
panic(errors.Newf("key kind %s is not a range key kind", kind))
}
}
// decodeSuffixValue decodes a single encoded SuffixValue from a RangeKeySet's
// split value. The end key must have already been stripped from the
// RangeKeySet's value (see DecodeEndKey).
func decodeSuffixValue(data []byte) (sv SuffixValue, rest []byte, ok bool) {
// Decode the suffix.
sv.Suffix, data, ok = decodeVarstring(data)
if !ok {
return SuffixValue{}, nil, false
}
// Decode the value.
sv.Value, data, ok = decodeVarstring(data)
if !ok {
return SuffixValue{}, nil, false
}
return sv, data, true
}
// encodedUnsetSuffixesLen precomputes the length of the given slice of
// suffixes, when encoded for a RangeKeyUnset. It may be used to construct a
// buffer of the appropriate size before encoding.
func encodedUnsetSuffixesLen(suffixes [][]byte) int {
var n int
for i := 0; i < len(suffixes); i++ {
n += lenVarint(len(suffixes[i]))
n += len(suffixes[i])
}
return n
}
// encodeUnsetSuffixes encodes a slice of suffixes for a RangeKeyUnset into dst.
// The length of dst must be greater than or equal to EncodedUnsetSuffixesLen.
// EncodeUnsetSuffixes returns the number of bytes written, which should always
// equal the EncodedUnsetSuffixesLen with the same arguments.
func encodeUnsetSuffixes(dst []byte, suffixes [][]byte) int {
// Encode the list of (suffix, value-len) tuples.
var n int
for i := 0; i < len(suffixes); i++ {
// Encode the length of the suffix.
n += binary.PutUvarint(dst[n:], uint64(len(suffixes[i])))
// Encode the suffix itself.
n += copy(dst[n:], suffixes[i])
}
return n
}
// EncodedUnsetValueLen precomputes the length of a RangeKeyUnset's value when
// encoded. It may be used to construct a buffer of the appropriate size before
// encoding.
func EncodedUnsetValueLen(endKey []byte, suffixes [][]byte) int {
n := lenVarint(len(endKey))
n += len(endKey)
n += encodedUnsetSuffixesLen(suffixes)
return n
}
// EncodeUnsetValue encodes a RangeKeyUnset's value into dst. The length of dst
// must be greater than or equal to EncodedUnsetValueLen. EncodeUnsetValue
// returns the number of bytes written, which should always equal the
// EncodedUnsetValueLen with the same arguments.
func EncodeUnsetValue(dst []byte, endKey []byte, suffixes [][]byte) int {
// First encode the end key as a varstring.
n := binary.PutUvarint(dst, uint64(len(endKey)))
n += copy(dst[n:], endKey)
n += encodeUnsetSuffixes(dst[n:], suffixes)
return n
}
// decodeSuffix decodes a single suffix from the beginning of data. If decoding
// suffixes from a RangeKeyUnset's value, the end key must have already been
// stripped from the RangeKeyUnset's value (see DecodeEndKey).
func decodeSuffix(data []byte) (suffix, rest []byte, ok bool) {
return decodeVarstring(data)
}
func decodeVarstring(data []byte) (v, rest []byte, ok bool) {
// Decode the length of the string.
l, n := binary.Uvarint(data)
if n <= 0 {
return nil, nil, ok
}
// Extract the string itself.
return data[n : n+int(l)], data[n+int(l):], true
}
// IsRangeKey returns true if the given key kind is one of the range key kinds.
func IsRangeKey(kind base.InternalKeyKind) bool {
switch kind {
case base.InternalKeyKindRangeKeyDelete,
base.InternalKeyKindRangeKeyUnset,
base.InternalKeyKindRangeKeySet:
return true
default:
return false
}
}
func lenVarint(v int) (n int) {
x := uint32(v)
n++
for x >= 0x80 {
x >>= 7
n++
}
return n
}