forked from cockroachdb/cockroach
/
batch.go
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/
batch.go
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// Copyright 2014 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.
//
// Author: Peter Mattis (peter@cockroachlabs.com)
package engine
import "github.com/cockroachdb/cockroach/pkg/util/hlc"
const (
batchTypeDeletion byte = 0x0
batchTypeValue = 0x1
batchTypeMerge = 0x2
// The batch header is composed of an 8-byte sequence number (all zeroes) and
// 4-byte count of the number of entries in the batch.
headerSize int = 12
initialBatchSize = 1 << 10
maxVarintLen32 = 5
)
// RocksDBBatchBuilder is used to construct the RocksDB batch representation.
// From the RocksDB code, the representation of a batch is:
//
// WriteBatch::rep_ :=
// sequence: fixed64
// count: fixed32
// data: record[count]
// record :=
// kTypeValue varstring varstring
// kTypeDeletion varstring
// kTypeSingleDeletion varstring
// kTypeMerge varstring varstring
// kTypeColumnFamilyValue varint32 varstring varstring
// kTypeColumnFamilyDeletion varint32 varstring varstring
// kTypeColumnFamilySingleDeletion varint32 varstring varstring
// kTypeColumnFamilyMerge varint32 varstring varstring
// varstring :=
// len: varint32
// data: uint8[len]
//
// The RocksDBBatchBuilder code currently only supports kTypeValue
// (batchTypeValue), kTypeDeletion (batchTypeDeletion)and kTypeMerge
// (batchTypeMerge) operations. Before a batch is written to the RocksDB
// write-ahead-log, the sequence number is 0. The "fixed32" format is little
// endian.
//
// The keys encoded into the batch are MVCC keys: a string key with a timestamp
// suffix. MVCC keys are encoded as:
//
// <key>[<wall_time>[<logical>]]<#timestamp-bytes>
//
// The <wall_time> and <logical> portions of the key are encoded as 64 and
// 32-bit big-endian integers. A custom RocksDB comparator is used to maintain
// the desired ordering as these keys do not sort lexicographically correctly.
// Note that the encoding of these keys needs to match up with the encoding in
// rocksdb/db.cc:EncodeKey().
type RocksDBBatchBuilder struct {
repr []byte
count int
}
func (b *RocksDBBatchBuilder) maybeInit() {
if b.repr == nil {
b.repr = make([]byte, headerSize, initialBatchSize)
}
}
// Finish returns the constructed batch representation. After calling Finish,
// the builder may be used to construct another batch, but the returned []byte
// is only valid until the next builder method is called.
func (b *RocksDBBatchBuilder) Finish() []byte {
repr := b.getRepr()
b.repr = b.repr[:headerSize]
b.count = 0
return repr
}
// Len returns the number of bytes currently in the under construction repr.
func (b *RocksDBBatchBuilder) Len() int {
return len(b.repr)
}
// getRepr constructs the batch representation and returns it.
func (b *RocksDBBatchBuilder) getRepr() []byte {
b.maybeInit()
buf := b.repr[8:headerSize]
v := uint32(b.count)
buf[0] = byte(v)
buf[1] = byte(v >> 8)
buf[2] = byte(v >> 16)
buf[3] = byte(v >> 24)
return b.repr
}
func (b *RocksDBBatchBuilder) grow(n int) {
newSize := len(b.repr) + n
if newSize > cap(b.repr) {
newCap := 2 * cap(b.repr)
for newCap < newSize {
newCap *= 2
}
newRepr := make([]byte, len(b.repr), newCap)
copy(newRepr, b.repr)
b.repr = newRepr
}
b.repr = b.repr[:newSize]
}
func putUvarint32(buf []byte, x uint32) int {
i := 0
for x >= 0x80 {
buf[i] = byte(x) | 0x80
x >>= 7
i++
}
buf[i] = byte(x)
return i + 1
}
func putUint32(b []byte, v uint32) {
b[0] = byte(v >> 24)
b[1] = byte(v >> 16)
b[2] = byte(v >> 8)
b[3] = byte(v)
}
func putUint64(b []byte, v uint64) {
b[0] = byte(v >> 56)
b[1] = byte(v >> 48)
b[2] = byte(v >> 40)
b[3] = byte(v >> 32)
b[4] = byte(v >> 24)
b[5] = byte(v >> 16)
b[6] = byte(v >> 8)
b[7] = byte(v)
}
// encodeKey encodes an MVCC key into the batch, reserving extra bytes in
// b.repr for use in encoding a value as well. This encoding must match with
// the encoding in engine/db.cc:EncodeKey().
func (b *RocksDBBatchBuilder) encodeKey(key MVCCKey, extra int) {
length := 1 + len(key.Key)
timestampLength := 0
if key.Timestamp != (hlc.Timestamp{}) {
timestampLength = 1 + 8
if key.Timestamp.Logical != 0 {
timestampLength += 4
}
}
length += timestampLength
pos := 1 + len(b.repr)
b.grow(1 + maxVarintLen32 + length + extra)
n := putUvarint32(b.repr[pos:], uint32(length))
b.repr = b.repr[:len(b.repr)-(maxVarintLen32-n)]
pos += n
copy(b.repr[pos:], key.Key)
if timestampLength > 0 {
pos += len(key.Key)
b.repr[pos] = 0
pos++
putUint64(b.repr[pos:], uint64(key.Timestamp.WallTime))
if key.Timestamp.Logical != 0 {
pos += 8
putUint32(b.repr[pos:], uint32(key.Timestamp.Logical))
}
}
b.repr[len(b.repr)-1-extra] = byte(timestampLength)
}
func (b *RocksDBBatchBuilder) encodeKeyValue(key MVCCKey, value []byte, tag byte) {
b.maybeInit()
b.count++
l := uint32(len(value))
extra := int(l) + maxVarintLen32
pos := len(b.repr)
b.encodeKey(key, extra)
b.repr[pos] = tag
pos = len(b.repr) - extra
n := putUvarint32(b.repr[pos:], l)
b.repr = b.repr[:len(b.repr)-(maxVarintLen32-n)]
copy(b.repr[pos+n:], value)
}
// Put sets the given key to the value provided.
func (b *RocksDBBatchBuilder) Put(key MVCCKey, value []byte) {
b.encodeKeyValue(key, value, batchTypeValue)
}
// Merge is a high-performance write operation used for values which are
// accumulated over several writes. Multiple values can be merged sequentially
// into a single key; a subsequent read will return a "merged" value which is
// computed from the original merged values.
func (b *RocksDBBatchBuilder) Merge(key MVCCKey, value []byte) {
b.encodeKeyValue(key, value, batchTypeMerge)
}
// Clear removes the item from the db with the given key.
func (b *RocksDBBatchBuilder) Clear(key MVCCKey) {
b.maybeInit()
b.count++
pos := len(b.repr)
b.encodeKey(key, 0)
b.repr[pos] = batchTypeDeletion
}